Headphone attenuation adapter

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Passive Headphone Attenuator

attenuator-1

5 reasons to use an attenuator in the headphone cable.

  • Some headphone amplifiers may have way to much power to safely drive high efficiency headphones like IEM’s or even ‘normal’ higher efficiency headphones.
    When too much power is applied by accident (IEM’s or headphones lying on the table and the volume is turned up, accidentally, for instance) these headphones may burn out or get damaged voicecoils.
    This can be an expensive mistake !
    So for these types of headphones an attenuator that lowers the output power substantially is very welcome.
  • some headphone amplifiers may have a background hiss that becomes (annoyingly) audible with sensitive ear-/head-phones.
    Attenuation at the input of the amplifier is pointless in this case as the noise is NOT coming from the source but the amplifier circuit itself and is not volume control dependent either in most cases.
    Instead attenuation has to be performed at the output side of the amplifier to lower the noise voltage along with the music signal. This way the noise floor becomes inaudible again and the music sounds much better.
  • Sometimes the volume control only has a small ‘workable’ range where the headphone already plays pretty loud when the volume control is just barely turned up. Leaving the rest of the volpot range unusable.
  • Some amplifiers perform (sound) better at somewhat higher output levels. In this case an adapter may improve sound quality.
  • Some headphones really should (want) to be driven from a low output resistance source. A 33Ω or higher output resistance may affect the sound quality/tonal balance in a negative way. The adapter lowers the source resistance to around but at the expense of a little more than -20dB attenuation.

A commercial version of this attenuator can be found HERE
Also iFi makes a similar adapter

In all the above cases a passive attenuator is needed/desired.
The difficult part here is that (Multi-Armature) IEM’s are usually very low impedance, generally between 8Ω and 32Ω and perhaps require a low output R of the amplifier in order to sound as intended. A high output resistance can quite noticeably change the sound !
Some sensitive headphones can also be relatively high impedance (up to 100Ω) but these are rarer and don’t really need a low output resistance to begin with.

Most multi-armature IEM’s have wildly varying impedances all across the audible frequency range.
Single driver ear/headphones usually just have a single mpedance peak (in the ‘bass’ region mosytly) and ‘upper treble’ region.
Because these low impedance ear/headphones have considerable impedance changes the frequency response (and thus tonal balance) will also change substantially when an amplifier output resistance above 1Ω is present.

Most modern phones/tablets/DAP’s/(portable) amplifiers have output resistances below 1Ω, though a few can be as high as 10Ω.
The reason for this change in tonal balance is not caused by the damping factor (as many still believe) but simply caused by voltage division.
To keep de frequency response as ‘flat’ as possible a low output resistance amplifier is essential.
If you are looking for more information on output resistances and the influence it has on the frequency response of (some) headphones you can find more info HERE

For this reason it isn’t wise to just mount a simple series resistance in series with the headphone as these increase the output resistance to substantially high values, 100Ω or more is not impossible.
Headphone adapters of 20Ω, 50Ω, 75Ω or even higher may work well with some specific IEM’s but most will not sound good at all with these ‘impedance adapters’.

So you probably need an adapter that provides a ‘decent’ load to the amplifier. This is because most amplifiers/DAP’s/phones don’t like to see very low impedances connected to its output.
It also needs to provide a substantial attenuation if we want to achieve goals like better volpot travel, protection against blowing it up and or noise reduction.
About 20dB attenuation is needed to achieve this.
10dB is close to being a 50% in perceived loudness (volume level or SPL).
20dB is thus about 25% in perceived loudness (volume level or SPL) and a very practical value.
We also need the adapter to have a low output resistance so the tonal balance remains the same as when the ear/headphone was connected directly to a low output resistance amplifier.

What the adapter will do

The adapter will always provide a load of around 35Ω to the amplifier. (Almost) regardless of how high- or low-Ohmic the connected headphone is.
Even when you short the headphone (make it 0Ω) the load the amplifier ‘sees’ is still 33Ω. So a short in a headphone cord will never short the amp.
The amplifier thus always ‘sees’ a constant resistive load of 35Ω

From the perspective of the headphone the numbers differ.
When you have an amplifier with say a 30Ω output resistance, the ‘source resistance’ that drives the headphone will always be be around 3Ω
When you have an amplifier with a 120Ω output resistance the ‘source resistance’ that drives the headphone will still be around 3.2Ω
When you have an amplifier with a 0Ω output resistance the ‘source resistance’ that drives the headphone will be around 3Ω
All headphones (regardless of their impedance) will thus always be driven by a 3Ω output resistance source, regardless of the output resistance of the connected source.

For sources with an output resistance above 10Ω this comes with a small penalty in the form of more than 20dB attenuation.
It attenuates around 20dB for all headphones when connected to an amplifier with an output R below a few Ω.
It attenuates around 26dB for all headphones when connected to an amplifier with an output R of around 30 Ω.
It attenuates around 33dB for all headphones when connected to an amplifier with an output R of around 120 Ω.

To create an attenuator that has these properties only 4 (cheap) resistors, a plug, socket and some wire is needed.

Of course you can buy these adapters but they are usually quite pricey.
If you have a soldering iron , a headphone plug, a headphone socket, some resistors, wire and some skill you can easily make these adapters yourself. If not it may not be too hard to find someone nearby who can make one for you.

So how about making one of these yourself…

This attenuator is based on a TRS stereo Jack plug which can be 6.3mm(1/4), 3.5mm(1/8) or even 2.5mm.
TRS stands for: Tip, Ring and Sleeve. Tip = Left channel, Ring is Right Channel, Sleeve = ground (aka ‘common’).
You need a (male) plug and a (female) socket and can make a small extension cord.
The mechanical construction is something you have to figure out yourself depending on plug size, room in the plug etc.
You can even make a cable with a 6.3mm plug and a 3.5mm socket so you don’t need an adapter to connect a 3.5mm plug into a 6.3mm desktop amplifier socket.
You can try to mount the components in the plug itself if there is enough room for it.
If this is not possible you can make a small extension cord with the resistors externally in a small enclosure (for instance a short piece of electric piping with shrink tubing around it)

stereo-32-ohm-adapter-tube
It is IMPORTANT to connect the resistors, that are connected to the Sleeve, directly TO the sleeve of the PLUG and NOT to the sleeve of the socket (upper schematic shown above)
If you mount the resistors OUTSIDE of the plug then the resistors that are connected to the Sleeve MUST have their OWN wires going from the resistor to the Sleeve of the plug. Do NOT combine these wires nor connect the return wires to the socket end. (lower schematic shown above).
Mounting these resistors somewhere in the ‘common’ wiring or on the socket creates a problem.
The reason for that is that the wire resistance of the used cable becomes a (substantial ?) part of the attenuation circuit in that case because the 3.3Ω resistors are very low in value. This could alter the stereo image.

Those low value resistors therefore MUST be connected directly to the Sleeve of the plug (male amplifier side).

The resistors can be carbon or metalfilm and don’t have to be wirewound or ‘special’ low inductance type. The 33Ω can be a 0.5W rated resistor, the 3.3Ω can be 0.3W to 0.5W.
Higher power ratings are not needed, not even when connected to amplifiers that can easily deliver 3W into 32Ω.
The reason you don’t need a higher power rating (Wattage) for the resistors is that the ear/head-phones used are high efficiency anyway. These headphones thus require very little power to play very loud.
Music signals do NOT consist of continuous power anyway but consists of very short peaks therefore the average power levels are quite low.
Small wattage resistors thus do NOT heat up even when the amp is playing loud so the power rating of small resistors is MORE than enough.

The adapter circuit shown above is suited for headphones ranging from 4Ω to 100Ω.

When you cannot make the adapter yourself or don’t know anybody that can then this adapter can also be bought ready made as it is being manufactured by G1217.
It can be ordered directly from the G1217 website.

attenuator-1

Using the output resistance of an amplfiier

When the amplifier itself already has an output resistance of around 33Ω you can even make an attenuator with just 2 resistors in the plug.
It does exactly the same as the attenuator above except the 33Ω resistors in the plug have now been replaced by the output resistance of the amplifier.
With amplifiers like the Musical fidelity v1 and v2, as well as some of these cheap Chinese Bravo/Indeed/Miridy amplifiers and also the Garage 1217 amplifiers set to ‘M(edium)’ output R setting the circuit below can be used to make an attenuator.

stereo-adapter-G1217In this case it is also VERY IMPORTANT to connect the resistors directly to Sleeve of the plug !

The adapter shown above can absolutely NOT be used with low output R amplifiers because the load resistance will be too low (< 3Ω)
The power rating of the 3.3Ω should be between 0.5W and 1W.

With these adapters you can safely connect sensitive ear-/head-phones to ‘potent’ and or noisy amplifiers.
The volume control range will also be MUCH better and the sound quality is NOT degraded.
In fact it may even improve as the noise level is lower and amplifiers usually perform better at higher output levels.

Balanced

The adapter as shown above will work with most equipment.
Just not with balanced outputs.
Normal amplifiers have a single signal (one for each channel) which is connected to a common return wire (often called ground)
Balanced amplifiers basically have 2 amplifiers which have the same signal on it but in opposite phase. The picture below illustrates the principle. The drawing is from www.tubecad.com which is a great source of info about amplifier designs.

balanced.png

A balanced amplifier has double the output voltage of a normal amplifier.
There is a small ‘but’ here because the maximum output voltage will only double when the output stage is able to deliver double the current as well.
Some devices simply aren’t able to do this and limit the max. output power due to current limiting of the amplifier design.

Most balanced amps (by design) would have to be able to provide double the current as well though.

With a single ended amplifier the output voltage, for instance, would be 1V (just a random number used here for illustrative purposes only) and this would be 31mW in 32Ω.
When the same signal is sent out balanced the ‘other’ amp that is now connected also will have a 1V output signal but in opposite phase.
This means: when one amp is at the ‘top’ of the signal there is +1Vrms and the other active amp at that same moment is -1Vrms.
The voltage difference between the 2 amp outputs (where the headphone is connected to) thus is 2Vrms. It is doubled in voltage. Double the voltage in the same resistance also means double the current.
Power = voltage x current so the power is 2 x 2 = 4 times higher = 128mW in 32Ω.
4x the power (= 2x the voltage) is an increase of 6dB in amplitude.
That is quite audible….

The output signal of the Left and Right channel thus are NOT connected like in normal headphone outputs.
Furthermore balanced outputs must NEVER have any of the Right an Left channels connected. You run a chance of blowing up the amplifier in question.

So to be able to use a headphone on a balanced amplifier you need to have 4 wires (2 pairs of 2 wires) which must be connected to a 4-pin connector or 2 pieces of 3-pin connectors.

There is a catch here which is that unlike ‘normal’ 3-pin headphone plugs (The so-called TRS Jacks) which regardless of size (2.5mm, 3.5mm or 6.3mm) have a pretty standard configuration. Tip = L, Ring = R, Sleeve = ground.

Below the universal schematic for a balanced headphone amp attenuator.

stereo-32 Ohm adapter tube balanced

As can be seen there are no connectors specified. The reason for that is that there is no standard and not everyone uses the same pinning.

Source side is the amplifier side, headphone side is of course the side that must be connected to the headphone.

One could easily make an attenuator with just 2 resistors which will work just as well.
BUT the 2 resistors are there for 2 good reasons.
A: The balanced signal stays perfectly balanced
B: When accidentally the L and R load are connected the source will NOT blow up and is protected against over-currents.

Connectors

Now we know what the input and output signals are we must find out which connectors are used and what their pinning is. In other words which signal(s) should go on which pin(s).

connectors TRRS etc

Above on the left there is the well known TRRS jack (usually 3.5mm) which is found on many headphones these days. These are NOT used for balanced signals in general but there are manufacturers that (mis)use these connectors for this purpose.
Never connect headphones with a TRRS jacks to balanced amplifiers when these headphones have a microphone and/or small remote in their headphone cord.
The 4th connection in this case is needed for the microphone and/or remote control.
There are 2 ‘standards’ for these plugs CTIA (Apple devices) and OMTP (most other brands) so the remote/mic of headphone A may well work with device B but not with device C for instance.

When unsure about your connector THIS is a great website that might answer your questions.

So be careful with the TRRS jack.
Below a few possible pinnings of gear with a 4 pin TRRS jack connected.

TRRS

As most of these aren’t specifically for headphones below a listing of the 4 main configurations of this TRRS plug.

TRRS audio.png

You need to find out what pinning is the correct one for the headphone AND is present on the amplifier/source.

The most common connector is the TRS jack (also in 2.5mm, 3.5mm and 6.3mm)
TRS.png

These are rarely used for balanced signals and in that case (Pono Player) you need 2 of those plugs, one for R and one for L.

One can never use a single TRS jack for balanced stereo signals but is almost always used for (single ended) stereo signals.

The mono plug only has a sleeve and tip and is often found on the end of a microphone.
It can only handle one signal (left or right for instance). 2 of these can be used for stereo signals (even balanced is possible with 2 of these plugs) but ONLY if the socket is a ‘mono’ socket as well.
NEVER plug a mono plug in a stereo socket. This could lead to damage of the connected source.

Another plug that is sometimes used for headphones is the 3-pin XLR (or mini XLR) or the 4-pin (mini) XLR.

The 4-pin XLR is suitable for balanced stereo signals.
You need 2 of those 3-pin XLR’s for balanced stereo headphones.
Below the most common configuration for 3-pin XLR plugs. Note that the pin numbering drawing of the XLR plugs above is valid when seen from the actual plug side.
When soldering wires onto these plugs you must realize what the pin numbering is on the solder side (mirrored from the plug side !).

XLR-3

The most common usage is balanced. This is standardized and all XLR sockets in (pro) XLRaudio equipment is usually connected that way. Most (balanced) high-end equipment often uses this plug. Sometimes the XLR socket is even combined with a TRS socket (see picture on the right).

Pin 1 is the ground. The pins (male connector) are all equally long but in the socket (female) the 1 socket is slightly longer. This way the ground is connected before the signal wires preventing loud ‘hums’ when plugging and un-plugging.

The 4-pin XLR is not used that much in audio but is gaining in popularity for balanced headphones as you need just one (professional quality) connector.
Below the most common usages for this plug. The HIFIMAN connector is by no means a standard but most manufacturers still use this pinning.

XLR-4

Connecting the attenuator.

Once you have determined what plug(s) you need and how they must be connected you can create an attenuator that has the same properties (in impedances and damping) as the G1217 adapter except for balanced amplifiers headphones ONLY.

It can NOT be used with single ended (3 wire) headphones.
In case one makes a mistake with wiring the headphone or accidentally or connects a 3-wire (TRS jack) headphone you can rest assured the amplifier/source will not be destroyed in the process. The ifi one does not offer such ‘protection’ when used in balanced mode.

Because of the many possible configurations and connectors such an attenuator has to be custom made. Some manufacturers offer converters or conversion cables from one plug to another. Beware that here too you will have to pick the right one for the job.

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Comments
  1. Dave says:

    “The attenuation is also 20dB but the amplifier ‘sees’ a higher load of around 35Ω.”

    You have a very strange definition of “higher load”. What you maybe mean to say is a higher load-resistance. A 200W light bulb is a higher load than 10W bulb, but is a lower resistance.

  2. Solderdude says:

    correct Dave … a higher load-resistance.
    It’s why I mentioned the 35Ω resistance as a load it ‘sees’.
    The actual load (as in power) is 2x lower than when a 16 Ohm adapter were used.

  3. Trev says:

    Would a Shure adapter kit (http://www.headphone.com/products/shure-adapter-kit) work in the same way – ie not changing the sound.
    I just got a Little-Bear P1, and can barely get above the channel imbalance on the Vol. pot without my blowing my ears out. All my phones have in impedance between 30-32 ohms, and a sensitivity of 95-100db. Was thinking about trying to mod the amp with a low gain switch, but this adapter seems way easier (still thinking about modding the amp, but that a different time/place)

    Cheers

    • Solderdude says:

      Do you mean the EAADPT-KIT ? In that case the tonal balance could change depending on the volume setting but to which extend depends on the impedance plot of the used headphone(s).
      Most likely Tyll’s plots ( http://www.innerfidelity.com/headphone-measurements ) could give some answers. The ‘flatter’ the impedance plot is the less effect the volume control may have.
      With some headphones it may even sound better, with others it may sound worse.

  4. Trev says:

    Yes, that was the kit I was referring to. I’ll look into the plots.
    So, for now, let’s take my Fidelio X2 (which I see have a peak below 100hz). They have an impedance of 30 ohms, and sensitivity of 100db. Using my Fiio X3 as a DAC, MusicBee as a player, EQ (electri-Q) flat – but a -40db pre-cut I’m typically setting the vol. at 9-10 oclock on the Little-Bear. What would be the best resistor values to use? (I assume I can use your last example). What is the formula used to calculate the value – so I don’t need to keep asking.

    Thanks for your time. I have some other questions about modding the amp, but I’ll save that for the forums.

    • Solderdude says:

      The P1 has an output resistance of around 33 Ohm so you can use the 2 resistor solution.
      Unfortunately I don’t have the Shure attenuator so cannot say how much resistance it has/adds.
      Let’s assume it is set to 100 Ohm (so about 10 dB attenuation) then the bass will be boosted by about 1.5dB.

      The formula to use is Ohms law.

      (headphone impedance)/(headphone impedance+series resistance).
      Of course this will give you only factors.
      Factors can be converted to dB.
      Go to: http://www.sengpielaudio.com/calculator-FactorRatioLevelDecibel.htm
      scroll down to the ‘Conversion: Gain G, Voltage ratio AV, and Power ratio AP’ calculator and fill in the ratio in the middle calculator (Voltage ratio) and enter the found number (for instance 0.15) and click on calculate.
      Now you have the attenuation in dB.

  5. Tikvar says:

    The Sennheiser HD 558’s and HD 598’s are rated at 50 Ohms, but have an impedance spike of 280 Ohms at the 95 Hz mark.
    http://graphs.headphone.com/graphCompare.php?graphType=7&graphID%5B%5D=2861&scale=30
    The bass sounds very loose and lacks punch. There is audible bass distortion when plugged into the PC soundcard line out. I’m not sure what the output impedance is for the line out, maybe 10 ohms? I couldn’t find the impedance output specs for my motherboard. The HD 558’s are very sensitive, usually 10 or 12 is the max level that I can tolerate. The headphones input jack is very noisy and severely distorts the bass response. Sound pressure level of the headphones is (SPL) 112 dB (1 kHz/1 Vrms)
    http://en-us.sennheiser.com/audio-headphones-high-end-hd-558

    What value of resistors would you use to compensate for that impedance spike and reduce the flabby bass response?….while still getting enough volume from the headphones.

    Thanks

    • Solderdude says:

      The line-out is not normally used for driving headphones.
      The output R could well be 50 Ohm or higher for the line-out.

      The headphone out is louder and should be able to drive 32 Ohm loads.
      Also it seems you need attenuation and a low output R

      I would try the 33 Ohm version of the adapter from the headphone out.
      When you have to much attenuation you could increase the value of the 3.3 Ohm to ground to a value of 6.8 Ohm or even 10 Ohm
      The output R will become somewhere around 5 Ohm which should be enough for the HD558.

      Mostly the headphone out of onboard soundcards isn’t very hifi though.

      • Tikvar says:

        Thanks for your advice. I made an attenuator using an empty pill bottle and a cable. I used a 1/4″ female jack because the HD 558 has a giant plug and a 1/8″ adapter, which is weird.

        I used 33 ohms as the large resistor and experimented with the lower value. 3.3 was too high because the bass still sounded bloated. The HD 558 has that big impedance curve around the 95 hz mark. I was testing on dynamic good quality music on Foobar2000. I ended up using 2.2 Ohm resistors, which gave the best tonal balance and volume attenuation to my ears.

        The background hiss/hum is now gone from the headphone input, and there is no more big volume jump when adjusting it. The sound improved quite a bit! Cymbals sound cleaner and songs sound more dynamic – better punch and instrumental separation.

        I am so glad that I stumbled upon your webpage, Cheers!

  6. maisbass says:

    I just purchased the new Westone Am Pro 20’s IEM’s (I am a Bass player). They are rated at 27 ohms but the sensitivity is rated at 119db SPL at 1mw. They are extremely loud with the 3 leaf enabler bass preamp/headphone amp I’m using for IEM. Unfortunately there isn’t a spec on the impedance output of the Enabler so I was stumped on how to solve my problem until I came across this page.

    So I made the circuit suggested above with the 33ohm and 3.3 ohm resistors. Holy Cow! Not only is the annoying background hiss gone, but my signal no longer sounds over modulated. In fact my bass sounds warmer and fuller than before. Also I have way more taper volume control now. Problem solved!

    FWIW I tried the Shure travel kit with volume adjustment mentioned earlier here. It did work, but as stated, my tone changed depending on how I set the volume. It is definitely a good temporary workaround or backup, but that circuit you posted is the Bees Knees!

    Thanks so much for posting this. I realize I’m responding to an old post so this may fall on deaf ears, but I still wanted to express my gratitude for this information hoping someone will read this. Thanks!!!!

    • Solderdude says:

      It doesn’t fall on deaf ears. In fact this problem is something many people have.
      Realising not everyone is capable of DIY, Jeremy (of Garage 1217) is going to build and sell these adapters ready made. I hope they will become available around end of Sept. 2016.

      • MagicMike says:

        Thanks you for this article. I happen to have a bad mismatch of headphone impedance and DAC headphone output impedance.

        My DAC is Cambridge Audio DacMagic Plus with 50 ohm claimed output impedance, 32 ohm measured: http://kenrockwell.com/audio/cambridge/dacmagic-plus.htm#z

        My headphones are Beyerdynamic DT 770 80 ohm.

        There is WAY TOO MUCH bass with this combination, it is really unbearable.

        According to “1/8 Source Impedance Rule of Thumb” I should drive the headphones with an amplifier which has max. 10 ohms output impedance to get the frequency response intended by the headphone manufacturer.

        If I would follow “Using the output resistance of an amplfiier” example and connect only 3.3 ohm parallel resistors, would that make my DacMagic behave as it would have 3 ohm output impedance (from headphones point of view) and therefore cure the bass problem at the expense of maximum voltage (output)? If so, since I only need roughly 10 ohms output impedance, could I increase the resistors’ size to 10 ohm to have less attenuation (hiss is not a problem)?

        Thanks! 🙂

        • Solderdude says:

          There are a couple of things to consider here.
          Those are: max output level, output resistance, efficiency and impedance rise around the resonance.

          The expected ‘bass boost’ on a 33 Ohm output R (DAC magic) is just 0.6dB.
          So even with 0 Ohm output R the bass will just be 0.6dB ‘softer’.
          On a 10 Ohm output R the bass levels will still be 0.3dB higher and the difference will be 0.3dB.

          The damping factor change is very small. Back EMF current damping of the same stimulus will only be 30% higher which is nothing to write home about.

          Then there is efficiency. The 80 Ohm version = 106dB@1V.
          So directly driven peak levels of 112dB can be reached.
          Considering loudness of sounds are determined by the mids, which usually are about 15dB lower than bass levels, this means average levels of 98dB SPL can be reached pretty loud.

          With a 10 Ohm in parallel 0.6V can be reached = 104dB… again – 15dB = 89dB.
          This is already about half the SPL that can now be reached… with a bass reduction of just 0.3dB.

          Considering the bass of most DT770’s is already quite boosted by design and typically (at least , that’s my opinion, one-note type as well I reckon the gain in SQ won’t be very high and max SPL will suffer.

          Even more so with 3.3 Ohm. The maximum SPL would be around 80dB and bass levels would be approx 0.5dB lower.
          So I would reckon the bass problem would just be slightly less and the maximum SPL would be decimated.

          How does this headphone sound on other (low output R) sources ? Say a phone or other portable players ?
          If it sounds way better from them consider a dedicated amplifier.

          The output resistance of 50 Ohm is only valid for the SE line-out stage.
          Strangely enough the output resistance of the headphone stage is not mentioned.
          Just “32 ~ 600 Ω headphones recommended”.
          The 33 Ohm output R measured seems correct.
          R28 and R32 seem to be responsible (high wattage 33 Ohm resistors)
          As I have no idea of where these are in the schematic I wouldn’t recommend changing the values.

          • MagicMike says:

            Here’s the story so far: I listen to headphones mainly at work (office). I have Sennheiser HD600 (300 Ohm) and DacMagic XS (0.5 Ohm), but since much of my listening consists of rock and metal, I have found the sound lacking in bass department, somehow the growl and weight of bass guitar and bass drum were missing. In short, it was not ballsy enough for rock ‘n’ roll. I tend to use fairly low volume when listening to protect my hearing, maybe increasing the need for “loudness” kind of frequency response.

            I’ve read that HD600 is a bit bass shy compared to e.g. HD650, but since I did not want another pair of open headphones (which are not ideal for office use), I opted for closed Beyerdynamic DT770 since it got fairly good review from NvAwGuy: http://nwavguy.blogspot.fi/2011/04/beyerdynamic-dt-770-pro-80-review.html

            With DacMagic XS, Beyerdynamic has fairly neutral bass, maybe it could be even a tad more powerful. Even though the bass is okish, the problem with DacMagic XS is that the overall sound is not very enjoyable, it’s a bit flat, dull, dry and harsh. Just a bit, but still enough to start to bother me. I tend to agree with this review: http://www.technologytell.com/gaming/133185/cambridge-audio-dacmagic-xs-review-sometimes-hearing-magic/

            So now that I found out that I might actually benefit from replacing my DAC, I recently bought a Meridian Explorer² (0.47 Ohm). Bass with Sennheiser HD600 improved a lot and this seems to be a good match overall. With Beyerdynamic, the sound is somewhat bass heavy and bass is a bit one-noteish, it definitely could be tighter, or have less emphasis on lowest bass. Maybe I’ll switch back to HD600 for office use.

            Back at home I have a DacMagic Plus. It is a no-no for DT770 because of hugely overwhelming bass. Even tough the boost might in theory be just 0.6dB, my ears tell otherwise. Or then maybe both DacMagic XS and Meridian are lacking in bass department. DacMagic Plus works great with HD600, but I actually preferred the brighter sounding Meridian when quickly comparing the two.

            I’ll try to buy a couple of different size resistors in coming weeks, make the attenuator and tell you about the results with DacMagic Plus and 80 Ohm DT770.

            • Solderdude says:

              The HD600 is VERY close to the HD650. The HD650 has slightly more warmth/bass. Notice the word slightly. Both lack subbass extension. Because the HD650 is a tiny bit warmer one could also say the HD600 is a tiny bit brighter.

              The HD600 is not for you.

              The one-note bass thing is there in all DT770’s, at least the ones I owned and tried. Both the edition and pro versions. Some people don’t hear it.. I do and wasn’t able to modify it ‘out’.
              EQ helps a little bit (lowering the bass).
              The DT770-pro is great for monitoring purposes in studios. That’s where you see them the most.

              If you don’t mind spending about 30 Euros you should buy the HD662-EVO. It is better than the DT770 in many ways. Deep, not one-note bass, tastefully elevated and like the DT770 not bleeding into the mids (because of the small dip at 200Hz).
              Both have excellent uncoloured and clear mids, HD662-EVO is better here too.
              The massive treble peak of the DT770 makes it harsh and bright on some recordings music.
              The HD662-EVO peak is smaller and MUCH less high = better treble quality.
              Compare them and sell the one you don’t like again.

              Buy a supple non microphonic cable (3.5mm TRS) for the HD662-EVO. apply the mods (very easy) and lower the clamping force to your taste (also very easy), apply the velours pads and you can wear and enjoy them all day.

              • MagicMike says:

                Ok, now I have tried bunch of different resistors and definitely there is a less bass with 3.3 ohm attenuator and DacMagic Plus is still able to push out enough watts to make the cans sufficiently loud. Unfortunately the overall sound with Beyerdynamics is still bass-heavy and not that great overall, can’t recommend that combination. Maybe there is some burn-in effect taking place, since after few weeks of listening I don’t anymore find Beyerdynamics overly bassy with Meridian Explorer². Thank you for the HD662-EVO tip, I will be adding them to cart next time I have something to order from Thomann.

  7. Maisbass says:

    Cool that he is building these.
    I have to admit it wasn’t easy fitting 4 resistors in the 1/4″ TRS connector. I used 1w flameproof resistors which were kinda large. It was a tight fit. As for the 1/8th female connector, I used the Neutrik Rean connector.

  8. Ray Rational says:

    Hi everyone.

    A very interesting article, I found this site whilst I was looking for ways to match different headphones on the same feed. I’m building a comms system for a PA/mobile recording system I’m putting together and although the mic inputs from the headsets will be dealt with independently and present no real problems the stereo headphone feed is going to be a parallel run to each headphone station powered by a 20W (into 8 ohm) stereo amp. The headphones are mainly 400 ohm and there will be 2 to 8 headsets on the line at any time and it works on the principle that the more headsets plugged in the lower the overall impedance and the power increases, in the same way that studios sometimes do with chains of headphones on power amps.

    I was going to put a couple of generous wattage wire wound resistors across the amplifier outputs to act as dummy loads when no headphones are plugged in (500 ohm-ish… perhaps? Higher… 1K?) or when everyone is using single sided sets (I’ve both and will give a choice to engineers) and one channel is not used. Probably a couple more wire wound resistors (100 ohm?) in line (series) at the amp outputs to just trim the output down a bit wouldn’t be a bad idea. This network will be built into a vented box – which can have some fuses on it – which the amp connects to before converting to the 7 pin plug with the mic input etc).

    At the headphone station I will put a passive volume on the box so users can adjust their headphone volume to suit their needs and different manufacturer’s headphones can be matched. I was thinking of a 600 to 1K log pot might be in the right area. Although most of my headsets are 400 ohm, I have got 3 single sided headsets that have a lower in impedance than the others at 150 ohms. I was thinking that the volume would resolve the mismatch if they are used with other 400 ohm sets on the line (I don’t want the impedance to drop too low as the amp will then start to deliver too much power to all the phones). I have been thinking that some sort of attenuation or impedance matching might be in order; either in the headset connector (4 pin XLR as they are mono, the stereo headsets are on 5 pin plugs; it does give some room for resistors) or as a switchable option on the box. I’m not sure whether this requires 1 resistor in series – as I suspect – or perhaps 2 in a pad arrangement and what values might bring these 150 ohm headsets in line with the 400 ohm sets. I know resistance is different to impedance but I’m not sure it will matter in this case; could I just stick a 250 ohm resistor in series with the 150 ohm phones even though it will be fixed rather than frequency dependant in value? I did wonder about some form of impedance matching transformer but finding ones with the right values might be a challenge and is it really necessary?

    Although I know roughly what is needed I’m a bit shaky on all the values of the resistors and the volume pots so if anybody has any suggestions I’d be very grateful to hear.

    It is a cobble (but quite a nice cobble) as I thought I would use what is lying around here, having spent an awful lot on the main system. However I think the idea is sound and after spending 40yrs wiring PAs, studios and data rooms as well as other projects like factory automation, I can make this into a very tidy comms system; I can build and wire extremely well and understand the basic electronic principles of what is going on but I am not an electronics designer and the maths sometimes gets the better of me; give me circuit and I’ll make it happen.

    The master hub for the comms system will be in an outboard rack at the mixing desk and consists of a rack mount stereo mixer (little Shure), the amplifier which in this case is an old Sanyo hi-fi beauty that I’m making rack mountable and I might throw in a low level DBX compressor/ noise gate – that was rejected for the PA system – between the mixer and amp to help with noise cancellation and limit things a bit. Lines to headsets are presented to the station boxes on 7 pin XLRs which have mic, stereo headphones (I’ve checked the amp circuit and the output negatives can be tied) and there is also a DC light circuit to attract attention, powered by an old printer PSU of course; the recycling force is strong with this system! Push a large button on the station and they all light up at every station. This system is stereo because there might be instances where it is appropriate to send feeds from the desks (FOH, monitor and recording) into the comms systems so other engineers can hear something that is going on… or we might just want to listen to a CD or radio in downtime with coffee! (I have plans for a flight-cased coffee machine… I want a happy crew and musicians; even the mic stands have drinks holders!)The sounds can be routed through the master station stereo mixer so the mics are still in use as well or they can go straight into the amp and be selected, so cutting off any irritating chatter until someone presses a light, I realised the other day that the amp also makes it easy to record what is being said on the comms; hmmm, could be useful!

    I will make some flight cased sub-hubs with just a rack mounting mixer (I’ve got more little Shure mixers) and an outlet panel with 4 x 7 pin XLR to star out to the stations, a box with the volume, light and switch, and 4 pin and 5 pin* head phone sockets and the 7 pin connection to the hub. (I’m going to include a parallel Cat 5 socket to the 7 pin as a backup and so it can use existing Cat 5 runs. The hubs can be plugged radially off the master or daisy chained. Some hubs will only have mono mixers as they will not need a stereo feed as they are only dealing with headset mics (only the 3 desks require stereo input) but they will still receive stereo. I’m hoping to find a 2 way radio link at some point for a roving headset with a belt pack; it would be easy to connect to the mixer and the tape out on the amp.

    *It is a standard for a lot of comms systems but I think the reason for 2 different connectors for mono and stereo headsets rather than just 5 pin plugs for both is that quite often on comms systems twin headsets are wired for mono being speech only. In my case the single are mono and the twins are stereo for music although the mic inputs will be centre mono.

    This is a comms system first and foremost and as such a little quality deterioration or tonal shift (just a little…) by putting passive devices, resistors etc on outputs should not be a problem. Although in saying that the headsets are all high quality industry standard; Beyer and similar so it shouldn’t sound too bad.

    The whole project is unashamedly analogue, and is well stocked with Klark Teknik, Drawmer and other great analogue outboard equipment with Soundcraft desks and the speakers are all Tannoy – FOH and the stage monitors – driven by 9 Lab Gruppen amps; 24 channels in all ranging from 300W monitor feeds to a 1000W for the bass cabs. I’ve actually ended up getting 2 speaker systems, one is 6 x Tannoy i12s and 2 x B225 bass cabs which will be increased to 8 + 4 as soon as I can find some more, the other… well I’m restoring speakers to put together an 80s Tannoy Wildcat system, it will consist of 16 x 12″ inch dual concentrics (Lynx and Bobcats) and 4 x up-rated Leopard bass cabs (up-rated with later more powerful Tannoy drivers).It is not a compact system with each stack being a perfect rectangle nearly 1.5 metres wide and 2 metres tall. RMS it is about 3.5 Kw. (Disco translation – 8Kw!) Although I have nearly enough speakers I will still buy ANY Wildcats I can get my hands on, even 15” speakers as I can use them as side-fill monitors or use the units for wedges.

    For me this is probably my final project (although I hope it goes on for many years) and it is the first time I’ve built a system for myself after many years of building for others. My days as a live engineer are over now as I have been ill for quite a while and my ears are not that brilliant, but I can put together something that I hope other engineers and musicians will enjoy and be quite special. I have rare vintage spring reverbs as well as quite a collection of valve processors (compressors, parametric EQ and preamps) as options. My mic collection is vast and full of choices from vintage ribbons to large diaphragm studio mics and all of the industry standards for vocals and instruments; I have 7 different bass drum mics and it’s a bit like that for everything on stage!

    I’ve always over-engineered my audio projects and I’m not breaking that tradition with my own system! It is a very complicated system, but a lot of the complication is to actually make the system easier and quicker to put up. The multicore system not only has sub-boxes around the stage and transformer splitting for monitors and the record desk; at the front desk it integrates with a long-frame patch bay, (the type that uses B gauge jack cords); it’s recycled BBC and CH4 panels. The batch bay went over 500 ways a couple of days ago and it will get bigger. But it means that the desk and racks can all be linked quickly using short multicores to the patch bay that will have a default patch and inserting equipment into the audio line at any stage is easy and centralised rather than having to plug everything in round the back of the mixer and racks individually; with 32 channels that saves heaps of time.

    It may sound strange building a PA system to a very high quality and then cobbling a comms system but I like inventive solutions that find uses for things outside their normal context, and several bits of old equipment get a new lease of life which is better than sitting on a shelf for a few more decades. If it works it has also saved me a bundle! Obviously I don’t want to fry expensive phones but they do take some welly and the volumes will need to be fairly high. It should be the high impedance that restricts the amplifier power from sending 20 watts to a headset if I get the values right.

    Just what happens with the system once it is built… well we will see, I will probably be very fussy about what it is used for; I bought the i series speakers because I knew I would be very precious about the Wildcats once they are restored to “as new”, I don’t think I’ll hire them out without me or that regularly which seemed a shame for a lot of the other gear so the answer was to get more Tannoys! This is not a party system nor do I see it doing bands that just want to be loud. It may have some power (the amps all together are about 10Kw) but I want it to have a walk in the park not pushed to the limiters; it really is about quality of sound. I think genres like jazz and acoustic and any other music (including some electronic) that would benefit from some clarity and warmth. Someone called it my labour of love last week, but then someone else called it the “the old gits hobby club”, I just figure I’ll build it and see what happens…

    Oh dear I’ve digressed and probably bored everyone to sleep! Well if anyone can remember my original comms resistor value queries and has some advice please get back to me; I’ll try to keep it brief next time!

    All the best, Meowsound

    • Solderdude says:

      That’s quite a story.
      The 20W @ 8 Ohm amp will deliver around 13V max.
      BUT it doesn’t have to reach those levels at all.
      It may be important to keep the ‘output’ resistance reasonably low for improved sound quality.

      What I would do in this case is use 8x a 100Ω potmeter (0.5W rated) and 8x a 100Ω resistor.
      The pots I would choose to be logarithmic if you want a wide adjustment range.

      From the + output of the amplifier each ‘channel’ has a 100Ω resistor going to the ‘hot’ pin of the potmeter. The ‘cold’ side of the potmeter must go to the – output of the amp (ground).
      Each headphone connected between the ‘wiper’ and the ‘cold’ side of the potmeter.

      This way you can use headphones between 32Ω and 600Ω and can adjust the level about similarly on each ‘channel’.

      The load this presents to the amp is around 25 Ohm and is perfect for such an amp.

      let me know if you have more questions and how this project turned out.

  9. Ray Rational says:

    Hello Solderdude

    Thank you for getting back to me; that information is exactly what I needed and will save me a lot of trial an error and with valuable headsets that is a probably good thing.

    Do you agree that strapping a couple of say 10 watt 1K wire-wound resistors across the outputs to act as default dummy loads to stop the amp ever being open circuit is a good idea? There has to be something there. 10 watts may be over the top but I thought 1K is high enough to keep the amp safe when single sided or no phones are plugged in; perhaps I’m getting this value wrong but I thought relatively high as the headphones will always pull the impedance down to a figure below their own value as the dummy load resistor and the headphones will be in parallel.

    It sounds like I probably don’t need the in line (series) 100 ohm resistors at the amp outputs.
    Although I’m making 8 passive station boxes with volume controls so I can cover any eventuality like lighting crews and stage management; it is likely that only 2 to 4 stations will be plugged in a lot of the time. I presume the 100 ohm pot values will still be alright if there are fewer stations on line. I think the headphones will never be lower than 150 ohms as any future purchases will all be 400 ohms which seems to be common for comms headsets.

    I did think of just having Beyer headphones (DT108 and DT109) so they were all perfectly matched; however having spent many years with a comms headsets on my head (it was quite a while ago but I still can remember the earache!) I decided I wanted a selection of headphones just because people’s ears come in a variety of shapes and different headsets become uncomfortable to different people. I have 3 different brands and enough of each to give a basic system of 3 to 4 of the same manufacturer if that is what people choose; so it could be just 3 x 150 ohm headsets being used. I bought the 150 ohm (RTS) headsets at a really good price but forgot to check the impedance of the 3 headsets, the other sets (Beyer and Tecpro) are 400 ohm which is the impedance I really wanted for daisy chaining in parallel but the RTS phones may suit some people so I’ll keep them for now.

    One thing I found out today whilst looking at specs of the 150 ohm RTS headsets that might make matching easier is that they have some hidden dip switches that can give a -10dB reduction from the normal volume on the phones.

    I have been thinking about the distance the headphone link has to cover. Whereas the mics each find a preamp at the nearest hub and the link for mics between the stage and the front of house desk will be sent at a balanced line level; the headphone bus though may have to cover 75 metres* or more in some venues. It would make it simpler if this does work OK and it is easily tested with a reel of cable, but I could install amplifiers in the sub-hubs and pass the signal at line level; the tape out on the Sanyo at the master hub would be a handy output for this purpose. If I do that though, the amps may end up with just one set of phones on their output.

    I did consider using multi-headphone amps; I have an ART that has 8 channels for studio monitor headphones. These would need to be installed in every hub. However it adds another level of adjustment and complexity and I’m not sure they would have the power for this with fairly high impedance headphones and they are not cheap; it could add £300 to £500 for 5 headphone amps. One 20 – 20 amp does keep it simple and provides reasonable power and I think it cost around £30.

    I described the headphone feed as a bus and between hubs it is, but it stars radially from each local hub to individual stations, but in the end all the headphones end up in parallel. The stations cannot be daisy chained as the mics are individually sent to the hub mixers, but the hubs can be chained or stared from the master hub or from each other.

    If there is room I will build some of the hubs into the racks that are in the various places, I already planned to do that with the master hub in the main outboard rack. One in the monitor mixer rack and the recording rack certainly makes sense as that covers my own crew areas. I will make at least a couple of self-contained hubs in flight-cases for other crew like lighting, stage management etc who might end up nowhere near any of my racks, The main component in the sub-hubs – beyond the mic mixer is the connector panel; this merges the various ins, outs, and lights to the 7 pin sockets for the station connections and hub links. If there was just one station on stage it could be plugged straight into the line to the master hub at the front of house desk without a sub-hub on stage. The line connection for mics can be swapped to a mic input at the master hub. I might just put one small power amp in one of the self-contained hubs so the two could work independently of the main comms as their own system. (It’s those chatty lighting techs again… ha-ha!)

    Great! I’ve just bought another stereo rack mount mixer on an eBay auction; not a Shure this time but an ART 416 in great condition for just £43.50 including post. I might use this one in the master hub as it has probably got the most features. One more stereo rack mount mixer needed and I think with the other 2 stereo and the 2 mono Shure mixers I have knocking around that’s enough to make 3 stereo hubs for the FOH, monitor and recording desks and 2 self-contained mono sub-hubs for other crews. Each hub can take 2 to 4 headset stations; this works out well with stereo hubs at all my desks where they may be needed to insert music (no more than 2 headset stations should be needed in these positions, perhaps 3 at the front desk on rare occasions which the ART can do) and the 4 way mono mixers for the self-contained hubs which still receive stereo on the headphones but can only take in mono (mic) channels.

    I was looking at possible ways to make one radio linked station today for a roving stage tech and I ran into some Tecpro comms systems; a starter pack of 4 wired comms was £1,260 new and going wireless it becomes astronomic; a used set of 2 stations with 3 batteries is on eBay for £2,250 The seller says it cost him £6,000 and although that may be a bit of an exaggeration looking at Canford who supply these things it probably isn’t far off! My 4 Tecpro headsets are the same as the ones on these systems and the new price for those is nearly £300 each. (No I didn’t, nothing like!) For an 8 way it really would be very expensive; at this stage I would sooner put the money into the PA/recording system, improving the sound quality as that is what will get more gigs.

    Besides wireless is OK but there can be issues like finding out nobody put the batteries on charge just as the gig starts! People now have got used to the idea of wireless everything but as most people on the comms will be in fixed positions and already have cables coming in to their equipment so it really is not the hassle some people imagine. I have found “wired” far more solid than wireless and not subject to interference.

    I am though going to try to find some cheap way of doing one wireless 2 way link from a belt-pack to a transceiver either at the stage sub-hub which is closest to the person wearing the belt-pack or better still the master hub as that has the tape out at line level on the amp and the mic input can go to the mixer. If the range is short and it has to be the sub-hub then a feed to the transceiver will have to be taken off the headphones bus but as it is down to headphone level that should not be a problem. When I originally thought of this I was thinking it could be fed into a DI circuit but that might screw up the impedance on the bus. I did wonder whether I could use Bluetooth but I know little about such things.

    Making my own comms system also allows me to make little personal touches; like a stereo jack input on the passive station with a 2 way switch that would mean engineers could plug the headphone monitor output from the desk into the station and switch the phones between the desk and the comms. It would switch over after the volume pot as when the phones are switched to the desk monitor the output can be adjusted at the desk; (to full!) leaving the pot in circuit on the comms feed. There will be available some decent dedicated headphones for monitoring at each desk as well as the comms headset (as well as an ex BBC pair of blue plug Sennheiser headphones wired for mono to a B gauge jack for plugging straight into the patch bay; they’re 1700 ohms but they will never end up on the comms line.) A lot of engineers prefer to use their own phones for monitoring, but some may find it useful to just use the comms headset for both purposes. I could have bought a new comms system but where is the fun in that?! As I say once the circuit is sorted I can build it, as well as wiring I have done a lot of metal work for my PA, studio and data projects.

    This is very much a sound system put together by someone who has used and built systems for companies for quite a long time and I want to make it as good an experience for both the engineers and musicians as possible. As well giving them a very thorough system with lots of options I want to get the little things right; stage situations can be tense enough without small irritations. A flight-cased coffee machine can sometimes save the day!

    Some people I have met whilst purchasing equipment have presumed that because this is an analogue project that I am some sort of old die-hard who hates digital; that is not actually true (well the die-hard bit isn’t) Although some have tried to find comradeship in that; I’ve been polite but some old sound techs do seem quite bitter about digital. I actually think digital sound is a wonderful technology. It has really opened up doors in music production to musicians, producers and people who just could not have made music without it. I really don’t think of it as “digital vs analogue” as both technologies can be mixed to great affect and eventually all sound systems – home or professional – end in analogue when the speaker moves the air (well at the moment you can also include the amp). Yes my home system is mainly analogue but there is a compact disc player (definitely vintage!) and I have no problem with plugging in digital sources like the computer; even if eventually it comes out of a Quad 303 with a pair of Tannoy Monitor Reds on the end! I have Monitor Golds in Lockwood Majors as well but they were shelved so the cabs could have a restoration far too long ago… but one day; sigh! They are a piece of history; so much music in the 60s and 70s was monitored and first heard on Tannoy Lockwood cabinets.

    I do have an interest in good vintage equipment and I like the way some of it sounds and the way it is built, but my love of Tannoys comes from a different route to most. My Monitor Reds and Golds were speakers I used professionally in the 70s; they were superseded by a hire company I used in 1980-ish. In about 81 I just happened to get a job with the same company and I found them languishing in a basement. I hauled them out and purchased them; the Golds cost me £150. I was always impressed by them but I never imagined they would reach such high prices 35 years later. The Monitor Golds have a sweeter top end compared to the Reds and are my preferred speaker.

    I chose Tannoy for this system not because they produce a distinctive sound (well all speakers do) but because they are accurate and honest. What they are given is what comes out, they are not complimentary and can be very revealing with a poor source although they will not add unwanted adulteration; it is the studio monitor within them (the Wildcat speakers used the same driver as the 80s Little Red Monitor and the 12″ SRM. I want to build a high quality and as neutral a system as possible and then provide my engineers with the tools to make the sound right for the music. I would sooner build a system without colour and then add it in a form that is controlled and sounds right.

    Most of the analogue equipment I’m using is of broadcast quality; they are industry standards and do not have a vintage sound really just an accurate sound and good functioning processors. Some – like Klark Teknik EQs and Drawmer compressors and gates – are still being made today without change. A “vintage” sound can be produced from my system – if wanted – by using the valve processors etc as necessary; if a dual valve compressor is put on the desk outputs rather than a Drawmer then the whole mix will take on a “valve” quality and individual mics can be given the valve treatment too. These processors are built to deliberately sound coloured just as some of my mic preamps have switchable plate voltages to give more warmth (pleasant distortion.) A lot of the valve gear here is some of the newest equipment I have, although there is some very old valve stuff too) but then this isn’t hi-fi, it’s about music production. I have a lot of gear that is not valve driven that can change the sound too. PAs don’t just reproduce the sound; they can help to create it…

    I’m building analogue because it is what I do best and with analogue quality and workmanship really is important. All my digital wiring has been very tidy (I’ve wired many thousands of racks) but it probably wouldn’t matter if I threw it together; it would still work as well. Analogue is so quality dependant at every stage of the chain that the standard of everything matters, unlike hi-fi there is a multitude of interconnection on a system like this, so it has to be good. Building analogue just has more joy! And for me using analogue live has its advantages; everything is laid out in front of you with all parameters having their own dedicated control that you can actually turn or slide with a nice smooth action; one day I’ll work out how many knobs are actually on the complete system but it is a hell of a lot. Digital sound has lots of unique things it can do well but when it tries to emulate the sound of a high quality analogue processing with plugins it never does it quite as well.

    As I say though the system will not suit every band; if you want stomach turning bass this system probably isn’t for you but if you want studio monitor quality then welcome, welcome to my machine!

    All the best…

    PS. Another long one and I’m sorry if posts like this break forum rules; off topic etc. I just get carried away…

    • Solderdude says:

      Aside from a very select few (mostly exotic transformer output) tube amps there aren’t any amps around that blow up when not loaded. Even when being played at max. volume.

      a 1kΩ resistor would dissipate max 0.2W on max output volume by the way.

      Even when no headphones are connected the 8 potmeters + series resistors would always present a 25Ω load to the amp anyway.

      The 100Ω series resistors in the ‘hot’ side of the potmeter should still be placed in all circumstances.
      These prevent the potmeters from receiving too much power and ensure a good load to the amp.
      Each 100Ω potmeter must have its own 100Ω resistor in the ‘hot’ path.
      Most certainly when long cable lengths are used.

      It does not matter if 0, 2, 5 or 8 headphones are plugged in.

      When all headphones used are the same type and all will play about equally loud you can choose linear pots.

  10. Ray Rational says:

    Hi Solderdude

    Just a quick one… really!

    It’s not that just that just the headsets that would be reduced in number sometimes, when there are only 2 headphones used, the station boxes with the volume pots would not be there either for the other 6 (the stations boxes are very close to the headsets, they could be used with a belt clip. If the headsets are not needed we would not cable from the hubs to the stations, so when 2 headsets are used there would only be 2 pots in the circuit.

    When I said “I wouldn’t need the 100 ohm resistors” I meant the 2 I had originally included at the amp outputs in my first post; I was going to put load resistors across the outputs AND 100 ohm resistors in line with the positives at the amp, but if I understand your circuit they are not necessary. I would definitely include your suggested 100 ohm resistors at each of the stations on the volume pot.

    I always thought a log pot would be best as different phones could always happen, we might get people who have there own and as I said, I like to give techs a selection to choose from so if the 150 ohm sets prove popular I will keep them. Although any future purchases will be 400 ohms and if nobody uses the 150 ohm sets I’ll replace them with whichever is more popular; the Beyer or the Tecpro headsets which are both 400 ohms.

    Yes the amp would probably stand being open circuit but I would prefer it wasn’t. Reliability is so important with this system, so is there any problem with a 1K resistor across the outputs? Is there a better value? There is a chance whilst the system is being rigged that the amp is left on without any stations plugged in so no pots or resistors at the headphone end, I would feel better if it had something on it.

    I always tend to be generous with my wattage on components but I didn’t realise I was so far out! I probably will still make it a 2 or 5 watt, being generous with wattage is not going to cause any problems.

    I do intend to put some inline fuses on the positives of the amp, just to protect my headsets if the amp does go DC. I will probably include an extra amp in case of breakdown; this can be the one in the self contained hub I mentioned in my previous post. In an emergency that hub can just replace the the desk rack master hub. But it is not something you want to happen as it would take some time to swap and some disruption around the desk.

    Thank you for getting back to me and I’m sorry if I’m being a bit slow, it has been rather frantic here in the last few weeks and I’m fairly tired.

    Al the best

    • Solderdude says:

      In that case I would connect a 10Ω in series with the output of the amplifier and from there on distribute the signal to the various pots.

      So amp output -> 10Ω -> distributer wire – > 100Ω -> 100Ω potmeter to headset.

      You can add a 1kΩ to the output but is not needed.
      No harm in adding a 1kΩ though even though technically it is not needed.

      For reliability it is more important to ensure the amp is not shorted by a distributer wire being shorted. So the 10Ω (10W !) series resistance is important.
      You could add a fuse in each line but that would have to be a max 100mA one or so.

      Amps do not care about minimum loads at all. They simply do not provide any current, just an output voltage.

  11. Ray Rational says:

    Thank you Solderdude; I do believe I’ve got it!

    I’ve obviously been around valve amps too long…

    Amp + __10 ohm______ x_________x______+BUS on to more taps for headphones
    I
    1K across the outputs if I feel like it!
    I
    Amp – _______________x__________x______-BUS on to more taps for headphones

    X marks the headphone taps on the bus that go to the pot via a 100 ohm resistor in series on +

    + and – taps after the 100 ohm resistor on + go across the 100 ohm pot (terminals 1 &3)

    – carries on to headphone. The wiper (terminal 2) becomes the hot for the headphones.

    The 10 ohm resistor is there to ensure that the amp never sees a short circuit.

    The 100 ohm is there to reduce the power.

    And the 1K ohm is not needed but makes me feel better!

    Thanks for all your help; now I will make it and it will be wonderful!

    All the best

    PS. I will let you know how it works out, but I have a lot to wire (I’ve got 1,500mtrs of mic cable coming next week) and I’m very slow nowadays so it might be a little while but it will be done.

    • Solderdude says:

      Looks like a perfectly good attenuator. Can even do balanced !
      The load the source will see is around 16Ω so it looks like a dual version of this one

      (when in -24dB mode) and also has a -10dB mode.
      It’s primary goal is to be used from portable sources (3.5mm TRRS) so to use it with 6.3 mm amps you would need an extra 6.3 mm adapter.
      That would have fitted in their travelling case as well.

      Because they use 4 wires (separated return wires) the resistors can also be in the socket section.

      The 16Ω load may work well with a lot of portable equipment as these are (generally) designed for this. Some portable sources, however, may show some subbass roll-off though.
      A 32Ω load may be better for usage with desktop amplifiers.

  12. Joseph says:

    How much power would it take to damage a balanced armature in ear monitor?

  13. Solderdude says:

    BA IEM’s can have power ratings between as low as 3mW (0.003W) but some are specified to 100mW (0.1W).
    The coils are very small and thus cannot dissipate much power.
    The power where the coils will burn out is not listed though.
    Impedances range between 8 Ohm and 400 Ohm so the voltages needed to burn the coils can also vary substantially.

    In any case the coils are VERY small and thus use VERY thin wires which means a very low power rating. Much lower than most dynamic drivers which have much larger voice coils so can handle more power.

    Accidentally blasting 1 or more Watts in them is quite likely to fry some of those tiny coils depending on make/model and impedance.

  14. Doug Adams says:

    This is a very helpful tutorial. I built this and it works well. It allows a lot more volume control range at very low volumes. I play music this way to fall asleep at night.

    My question is about building this for a portable Pono Player DAP. It has balanced outputs to drive the 2 cable balanced headphones. This is achieved by using two 3.5mm trs connectors on the player. Left channel on 1 connector, right on the other. The tips are the + and the rings are -. I know minus is different than single ended ground. How do I wire this adapter up? Assuming one adapter will be required for each cable?

    The pono player sounds great playing balanced headphones. Unfortunately there is even greater volume than single ended. 1 notch on the volume control above off is still too loud for sleeping. If it helps the Pono has 3.3 output impedance and the Mitchell & Johnson MJ2 hybrid headphones are 32 ohms.
    Thanks for this superb project and all of your help.

    • Solderdude says:

      I added info to make a balanced adapter as well.

      • Doug Adams says:

        Thanks Solderdude for this additional info on building balanced attenuators. Your explanation is very clear and easy to understand. The illustrations are very helpful. I will be building these for the Pono Player!

        The Pono sounds best in balanced mode but the extra 6db volume doesn’t help when I want to play at low levels. Your balanced voltage divider design solves the problem nicely. Thank you again.

  15. LG owner says:

    Connecting my LG tv speakers ( 6 ohm 10 watt x 2 ) directly from speaker wires to my 32 ohm headset – will i need to make a connector . Most older tvs had 3.5mm headphone out jacks with series resistors in the right and left channel lines. If i need them, what value resistors to use ??
    Thanks for any help you may have. LG owner

    • Solderdude says:

      Yes, an adapter may well be needed. 32 Ohm headphones usually are quite sensitive and play loud already on 0.5V to 1V. The TV will give around 7V on its speakers.
      When unattenuated you may hear background noise and volume control will be hard to do.
      You can probably only use the bottom few volume steps.

      Whether a single resistor can do the trick properly depends on the impedance of the headphone, how much it varies.

      I suggest to use/build the circuit as described here:
      https://diyaudioheaven.wordpress.com/tutorials/power-amp-adapter/

      R1 = 33 Ohm, R2 = 4.7 Ohm

      The voltage divider with 2 resistors per channel.
      I assume the TV has a common ground, when the output is bridged things get more complicated.

  16. Vaelus says:

    Hi Solderdude, does the Attenuator sold by garage 1217 and discussed here alter frequency response in any way? I tried the IFI earbuddy as my amp has some noise noticeable even with my 300 ohm HD 650 and while it got rid of the noise it also noticeably decreased the bass.

    The AMP has a 8 ohm output impedance so I dont think it is due to the output impedance being reduced.

    Would love to find a way to get rid of the noise without altering the sound.

    • Solderdude says:

      It should not affect the sound quality when connected to an amplifier that can drive 16 Ohm headphones BUT could affect the bass when the amplifier in question has relatively small output capacitor values or when the amplifier has a small maximum output voltage level.

      In that case of the small value output capacitors, say 100uF, the 300 Ohm load will create a roll-off point of 5Hz for instance where the 18 Ohm load of the IFI attenuator could shift the roll-off point to 90Hz resulting in an audible bass loss. The G1217 adapter won’t do much better in this case as the 33 Ohm load will give a 50Hz roll-off point.

      Another reason could be that the maximum output swing of the amplifier is not enough. The attenuator lowers the output voltage 16dB which is 6x. The max output voltage thus will be 0.16x lower as well. When the output voltage swing of the amp is 5V for instance the max. output voltage will be reduced to 0.8V. In the case of a relatively voltage insensitive headphone (300 Ohm) this means that bass may well be clipping and thus is reduced in level relatively to the mids. At the first onset of clipping most people do not hear this as ‘clipped’ distortion but rather as less bass before it starts to sound ‘distorted’.

      Then there is the subjective effect of a lower SPL level due to the way our hearing works (Fletcher Munson). When switching between 2 levels (unattenuated and attenuated) the bass appears to be much lower in amplitude relative to the mids.

  17. ‘You shouldn’t Connect IEMs to power amp adapter,because of a few mW power handling”
    My amp 10w/8ohm. I found suitable resistors for 30db attenuation,and for this resistor and for 16ohm it gives about 10-20mW.
    Isn’t that safe for IEMs?
    Or should we consider the tolerances of resistors too?
    Or after power amp adapter,should I Connect the headphone attenuation too?(is it good idea 2 times attenuation?)

    Is there any safe method to use IEMs for power amp adapter?

    Thanks

    • Solderdude says:

      A 10W/8Ohm amp can deliver 9V. Most likely a bit more (10V) when not loaded that much.
      The 20mW/16Ohm = 0.6V.
      24dB attenuation is needed.
      An IEM might need a lower output R than 3 Ohm, some specific ones work better on a higher impedance.
      Lets assume R2= 2.2 Ohm with 16 Ohm load = 1.9 Ohm
      R1 must be around 30 Ohm (thus either 33 Ohm or 30 Ohm in E24 values)
      The 30 Ohm resistor would need to be around 3W for continuous power but music isn’t continuous so a 1W resistor (for R1) will be enough.
      R2 can be 0.4W.

      When it still plays too loud you can make either R1 bigger (say 47 Ohm) or R2 smaller (say 1.5 Ohm)

      No need to use the headphone adapter after the speaker amp attenuator.

      Of course when you use the 10W amp with other headphones and calculate values for those headphones you can always use an attenuator after the speaker amp attenuator to make a better match for IEM’s.
      Shouldn’t perform any less than 1 attenuator.

      • So it is possible with these values.
        Can I ask u one more question about output noise.
        My amp1 have 50-60uV output noise.
        My amp2 have 0.3-0.7mV output noise.
        My amp3 have 0.1-0.3mV output noise.
        All of them 10w/8ohm.
        I am guessing output noise should be less than 4-5uV for sensitive headphones.
        So how much does my power amplifier adapter change my amplifiers output noise voltages?

        • Solderdude says:

          Noise levels are lowered in the exact same amount as the output power levels.
          When output voltage is lowered by 24dB so will the noise level be 24dB down.
          In case the IEM still shows hiss with say amp 2 you will have to increase the attenuation to the point where it is silent.

          24dB is a factor 16.
          So when you want to reach 5uV with amp 2 you will need 40dB attenuation
          amp 1 will be fine with 60uV noise as noise levels will be below your mentioned noise level with 24dB attenuation.

          • I did a few calculations.
            Amp is 8w,8ohm so 8volts.
            Amp noise 200uV.
            Let’s say we want to 10uV noise for headphones.
            So I need -26dB attenuation.
            This attenuation gives me 0.4volts.
            For 250ohm headphone 0.64mW
            For 60ohm 4.8mW
            For 16ohm 2.5mW.

            So I looked at your headphone power table and it seems 0.64mW isn’t enough to power a 250ohm headphone??
            What is The noise audibility voltages can be heard by headphones or IEMs??
            Does my amp is too noisy to use headphones?
            I start to think more power(like 40w 8ohm) can be better for wide range of headphones?

            • Solderdude says:

              0.4V is too little for headphones above 32Ohm. Consider most phones can put out between 1V and 2V and these are not able to drive high impedance headphones to great heights.

              0.4V in 250Ohm = 0.64mW
              0.4V in 60 Ohm = 2.6mW
              0.4V in 16 Ohm = 10mW

              Difficult to say what the noise level is for a headphone.
              This depends on the Efficiency and Impedance and how sensitive your ear is.
              A young person may hear noise in a quiet surrounding why someone 40+ may already have 10dB hearing loss and not detect any noise.
              Also the 200uV is this peak-peak ? rms ? in the audible band ?

              Speaker amplifiers in general are not designed for headphones and noise levels aren’t that critical for speakers.

  18. I also have one more question 🙂
    I have a dac output 50-ohm and 3.5volt peak to peak.
    Do you think that can I use the adapters to lower the output impedance and maybe I can power headphones directly?

    • Solderdude says:

      The DECware seems good. Also has crossfeed which narrows the ‘soundstage’ and seems quite versatile.
      Would make some changes to some parts though.
      Will work on 12V but you should realize the ground is at 6V in that case so if the 12V also feeds other circuits it will be problematic/

      The PA2v2 is not suited for driving high impedance headphones.
      With 3V voltage you won’t be able to get more than 1Vrms from it.
      It seems designed to drive 0.2W 8 Ohm small speakers.
      Any phone can reach those output levels.

      The Butte is a nice amp but requires 12V AC or + and – 12V (so 24V in total)

      The HD600 is more of a hi-fi headphone for enjoying music.
      It is open and lacks subbass extension and is comfortable.
      The DT250-250 has some issues between L and R and doesn’t have the refined treble of the HD600 but has excellent bass extension and is neutral.
      It is designed as a monitor not as a hi-fi headphone.
      Would recommend to try it (with an option to return it) or listen to it in music stores that carry it.

      The DAC output is 50 Ohm but may not be able to provide enough output current.
      DAC outputs are designed to drive impedances between 5k and 100k.
      It may work well, it may not. No way to tell unless one has the schematic.

      • I already saw in his forum,Steve says it is ok for 12v.But I will ask him for max. voltage.Price is also very good and it looks solid..
        Can you suggest me a closed back headphone with good sealing and its sound quality at the hd600 level?
        I am also looking for travel headphones because of their prices..
        Maybe beyerdynamic t51p?
        I should work 1,5 month without eating to buy hd600 😁

        • Solderdude says:

          There are no cheap closed headphones that have HD600 alike qualities. At least not cheaper than HD600.
          The T51P is hard to recommend. This is one headphone one HAS to audition before a buy or have the option of returning it.
          The fit is important (seal) for a good sound. It is an on-ear which is not very comfortable for many.
          I like the DT1350 (with EQ) but this one too is hard to recommend.

          The DT250-250 just is not refined in the treble. It doesn’t have to be as a monitor. It just must be ‘honest’ in tone.

          You could look into the ATH-M50X (not the old M50)

          For portable (open, not closed) the Koss PortaPro comes to mind.

          You should look into the Sennheiser HD569 for sure (closed over ear) but have not heard it.

          Always hard to recommend a headphone as not everyone prefers the same sound as I do.
          It is always a personal thing. Some people like Grado, Ultrasone or AudioQuest or like Beyer treble.
          They would not like what I would recommend.
          Trust your ears. headphones is personal audio so you should best decide for yourself what you like.

  19. Andrew says:

    This was an interesting read. I’m currently looking for a 4 pin balanced attenuator because my headphones are quite sensitive and I hear noise from the balanced output of my amp. Are there any commercial products you know of that do this? I’d get into building it myself but I’m hopeless at soldering.

    • Solderdude says:

      I don’t know if there are commercial versions around. I suppose not.
      Perhaps someone at DIY forums is willing to make one for you.
      You could also ask Jeremy at Garage 1217, perhaps when he has time could whip one up.

  20. Rob says:

    Thanks for the article. Firstly I have very little knowledge of electronics but I’ve put together a couple of succesful amps including an Objective 2. My electronics experience so far is very much soldering by numbers! I’ve recently bought a Bravo V2 and had a go at making the attenuator with two 3.3k resistors. It’s all soldered together nicely but it’s not attenuating the sound in any way. The volume is just the same. I do have sound and it sounds fine – it just hasn’t done anything to extend the travel of the pot. On the positive side I now have a 6.35mm to 3.5mm cable! Maybe the output impedance of the V2 is different to the V1 and this particular cable was recommended for the V1 Bravo? Hope you can help. Thanks.

    • Solderdude says:

      That’s because the resistors need to be 3.3 Ohm and not 3.3 kOhm.

      • Rob says:

        Ah! My mistake. That does give me a question though. Wouldn’t a 3.3k Ohm resistor have more resistance than a 3.3 Ohm? Clearly there’s something I don’t understand. Thanks.

        • Solderdude says:

          a 3.3k has 1000x more resistance than a 3.3 Ohm.
          As the 3.3 Ohm to ground provides an extra load to the 47 Ohm in the Bravo a voltage divider is made.

          Assuming no headphone is connected there will be 0.066x the output voltage across the 3.3 Ohm.
          A 24dB attenuation in this case. With a headphone connected it will be even more.

          When a 3.3k resistor is used 0.98x the output voltage will be there. 0.1dB attenuation which is inaudible. The resistance of the headphone itself is factors lower than the 3.3k in parallel so the 3.3k effectively has no influence.

          You may want to use a 5.6 Ohm instead of 3.3 Ohm with the Bravo.

  21. Rob says:

    I see. Thanks.

  22. Mick says:

    Hi.
    First off great article, this was just what I was looking for.

    I have just bought a Creative SBX AE-5 sound card and paired with my Bowers and Wilkins P7 head phones although sounds great gets loud very quickly. Using 0 – 20 on the Volume is all that’s usable on most tracks.

    I built the adapter, and yeah its great and works a treat … well almost.
    Now my volume range is nice and progressive all the way up to 85 – 90 for the same volume at 20 before the adapter.
    Here is the but…. Some of my tracks that have low volume there isn’t enough overhead left to be able to turn these up to my liking.

    So what I like to ask is which or both of the resistors is best to change to lower the attenuation.
    You say this is roughly 20db attenuation what values would you recommend to drop the attenuation to say 15 db.
    The Bowers are 22 Ohms and the SBX AE-5 has 1 Ohm output impedance

    Thanks.

    • Solderdude says:

      Hi Mick, The 3.3 Ohm resistors must become 10 Ohm. In this case the attenuation (using 22 Ohm headphone) = 15dB and the output R will become 7.6 Ohm.
      This may well be too high though but worth trying.
      It will probably lead to a +0.4dB in crease around 40Hz (lower bass)

      Perhaps using R1 = 22 Ohm and R2 = 6.8 Ohm is slightly better (5 Ohm impedance).
      I have not seen imp. measurements of the P9 but the P7 shows an increase from 25 to 29 Ohm (around 40Hz)
      This will give a 0.3dB increase around 40Hz.

      Give it a try and see if this works for you.

  23. Mick says:

    Thanks.
    I’ll give the 22 and 6.6 Ohm resistors a go See what it sounds like.
    But May end up sticking to the original design as it works brilliantly for 90 % of my music, just me being overly fussy.

    I’ll post back when the resistors turn up and Ive put it together

    Thanks again

  24. Not Jim says:

    About the statement:

    >The adapter shown above can absolutely NOT be used with low output R amplifiers because the load resistance will be too low (< 3Ω)

    Could this be corrected by adding an impedance adapter between the amplifier and attenuation adapter? And would a 20-ohm adapter be enough?

    • Solderdude says:

      Yes it could, but then you would have to use 2 adapters. In this case (when you have to make an adapter anyway) it would make sense to make the adapter with 4 resistors in it.

  25. Hsdw says:

    Hello, is it possible to make attenuator without adding impedance to the amp self output impedance(or just a little).

    I have Audioquest Dragonfly Red , it has 2.1v output + less than 1ohm output impedance.
    IEM are Andromeda, 115 db / 12 ohm. And it has a little background hiss, which is near unaudible when i listen to music, but noticeable on silent parts. I have ifi audio iEMatch, and it solves this problem perfectly in 1ohm(ultra mode). But physically it adds to much to the DFR dimensions.
    So i want to made the smallest adaptor that i can do, or build it inside DFR housing(there is a bit of free space there). So what kind of resistors do I need for this? My target is hiss suppression and near zero OI, but if this is not possible, than something lesser than 1 ohm.

    • Solderdude says:

      There are a few issues with this combo. AQ is not very forthcoming with the really important data here so will have to rely on John Atkinson’s findings.
      He concludes that the DFR can deliver 2.1V (higher than the other 2) but is not really suited to drive headphones. Even 300 Ohm is already too much. It seems to be designed to drive headphone amps.
      The measurements from JA tell me the DFR and 12 Ohm headphones is not a good idea.
      Even 30 Ohm is a challenge for the device and the output voltage (undistorted) has to reduced 5dB which means at 30 Ohm the max. output voltage has dropped to 1.18V.
      This calculates as the output stage having a max. output current of 40mA (55mA peak) which is a normal value for a lot of opamps.
      At 12 Ohm the max. output voltage is around 0.5V thus a reduction of 12.5 dB !

      To get best performance of the DFR the load resistance it wants to see must be as high as possible.
      In your case, when you want just little attenuation and low output R this is simply impossible to achieve with passive attenuators.

      As you have been driving the Andromeda with the DFR and don’t hear complaints about fidelity you probably never reached the max. 0.5V output voltage.
      This is quite likely as there would be peak levels of 128dB (so average levels of 110dB or so)
      This you can’t endure easily for longer than a minute or so.

      There is an opening here as you can loose a few dB and thus lower the noise level the same amount.

      Let’s assume 10dB reduction is desired (as the noise is just audible) and an output R of 1 Ohm is required (lower is not possible passively).
      This means R2 = 1.2 Ohm then R1 must be 3.0 Ohm. R load would then be around 4 Ohm which the DFR simply cannot handle.

      The ifi in ultra mode attenuates 24dB and loads the amp with 16 Ohm.
      This means: 0.65V max = 106dB peak = around 90dB average which is still pretty loud.

      It looks like the ifi solves the problem in -24dB setting.

      As it seems to be able to driver the 16 Ohm load and 12 Ohm load and can play loud enough lets make an adapter with a 13 Ohm Load and 20dB attenuation.
      R1= 1.2 Ohm R2 = 12 Ohm = – 21.5dB attenuation and 1.0 Ohm output R

      R1 is the resistor in series with the HP out and R2 the resistor to ground. The headphone is connected across R2.

      Which power rating is needed… At 12 Ohm the max output voltage = 0.5V = 0.04W.
      This is peak level so average levels in music are well below 0.01W when it starts to distort (clip)
      Those resistors thus can be really small. The smallest size that can be handled is about 0805 SMD resistors. Most of them are rated well over 0.1W so is not an issue.
      When you are adventurous 0604 sized SMD resistors are maybe an idea.

      It would be no problem to fit those SMD resistors inside when you are able to open it up and solder those parts in there. You would have to cut the traces to the HP out and insert the 12 Ohm there and solder the 1.2 Ohm from the HP socket signal to the HP socket out.
      The DFR would now suck as a source for a HP amp though as the max output voltage of 2.1V would be reduced to 0.04V.

      The Andromeda will put out max. 106dB peak = around 90dB average SPL. Still pretty loud for a headphone.

      Hope this helps.

  26. Hsdw says:

    Hello, thank you for response!
    So i ordered parts which i need, but i have additional little questions. Soldering isn’t problem at all.

    I have 2 cables, one have 1.3 ohm resistance, and other 0.3 ohm. I like the sq from 1.3 ohm, but 0.3 ohm cable is just superior in build quality, aesthetics and has better ear hooks. So i want to add 1 ohm impedance to the new cable. So i need to add 1ohm resistors to all of the cable “lines” ?
    Cable has 4 lines , but has simple trs jack, so 2 ground connecter to 1 jack ground. I should use 2 separate resistors for ground, or can solder ground in 1 resistor?

    If i want to play with attenuator’s output impedance, what is the rule of the resistance of the bigger resistor. Near all schematics on this page are something like the bigger one has 10x of the resistance of the small, and resistance of the small is total output impendance of the attenuator. So if i want 2 OI, i should take 2 and 20 ohm resistors, 4 ohm oi = 4 and 40?(If we do not consider the dragonfly as a source), 10x is a rule?

    Resistors has a power rating in watts, this is maximum power that they can hadle or what?
    And is there any reason to hunt for most accurate resistors, some has 5%, and others 1%.
    And which type is more suited for that? The resistors which are like “sausage”(sorry idk how they named in english) is kinda big to build it directly in jack, but they are cheap and avaible everywhere. The MELF resistors is not so big, but I will have to wait for them 2-3 weeks. The SMD chip resistors are in stock, but they seem too small, I don’t know, can I solder them, even if I get a thin sting.

    Thanks again, and sorry for the stupid questions.

    • Solderdude says:

      When each wire has 1.3 Ohm vs 0.3 Ohm in the other cable then adding 2.0 Ohm in the signal wires only will do. No need to use 4 resistors.

      The 10x rule gives about 20dB attenuation and an R out 0.9x the lower value.
      Of course the bigger the small value becomes the more attenuation one gets when the headphone impedance is lower.

      Power rating is continuous power. A 0.4W resistor thus can handle 0.4W in DC current and AC current.
      With music signals the average power levels usually are 10dB lower than the peak levels.
      So when a resistor is rated 0.4W it can handle music signals with peak powers of 4W.

      5% is enough. The drivers themselves sometimes differ 0.5dB which is around 5%.
      5% resistors usually are within 1%… there just could be ones that are worse to max. 5%.
      1206 sized resistors are easily soldered. They break easily though. You cannot bend them at all.

      SFR16 sized resistors are small and 0.5W rated

      • Hsdw says:

        So I realized that the best option for me would be a smaller copy of the iEMatch in the headphone jack. Just because this will be more universal, and I’m afraid that I can damage the coating of DFR, when I will heat it.

        I got 16 ohm and 1.3 ohm 1206 0.25w SMD and managed to make my first attenuator.
        Checked it with spare cable and this was ok. Pretty much the same attenuation, and hiss free.
        https://imgur.com/a/8SqkFjU sorry for the goofy scheme, is this ok? But for the perfect constructing of this(1206 are too long,so i placed them at an angle), i need a smaller 0805 resitors, but they are 0.125w. I hope that there will be enough for my purpose.

        I want to make it as much as possible, like the iematch in ultra mode (~1ohm ouput impedance). So i measured melf resistors inside , and i got 2×33 ohm, 2×15 ohm, and 4×1.1 ohm. So i guess, my target will be near 15 and 1.1 resistors. But why there is 2×33 ohm resistors, and how iematch can have 2.5 OI in high mode?

        • Solderdude says:

          The only concern I would have using SMD resistors this way is that they might crack if very little force is exerted on them when screwing the sleeve on the plug. 0.125W should still be O.K. but is already on the low side.

          The values may well be correct (they should have colour bands as well).
          Perhaps you can trace the wiring a bit.
          Hard to say how they come up with the quoted values for load and output R with these values unless more are hidden elsewhere ?

          • Hsdw says:

            Color codes was kinda weird, some of the resistors were identified, but some was wtf(yes i tried to reverse). So, i unsoldered them and measured. There is 2x 33ohm, 2x 15ohm,2x 3.3 ohm and 2x 1.5 ohm.
            So 15 + 1.5 is my desired target, but if the output R is 0.9 of the smaller value, than OI will be around 1.35 ohm, but ifi stated less than 1 ohm OI(or just ignore their specs?).
            And i guess 15 + 3.3 is -12 mode?
            But i don’t understand, why there are 33 ohm(maybe something for their s-balanced thingy).

            Anyway i will make 15 + 1.5 in jack using 0805 for the first time, and when I’ll get MELF, i’ll make attenuator using them(they are more powerfull, maybe physically stronger, and has more convenient dimensions).

            • Hsdw says:

              Again, made it in jack with melf resistors from iematch 15 + 1.5. Volume is a little bit higher than normal + noticeable a little increase in output imdepance compared to the original iematch. So I’ll try 0805 -> 16+1.1, to directly follow iematch paper’s characteristics : 16 ohm load + less 1 ohm( 1.10 -0.110) OI.

            • Solderdude says:

              Instead of MELF you could opt for mimiMELF which are rated 0.25W to 0.4W or use SFR16S which are miniMELF sized but have wires attached to it.

              I suspect the 3.3R and 15R are ‘fixed’ values and the 1.5R will be switched in parallel to the 3.3Ohm in the ‘ultra’ mode.

              3.3 + 15 results in: -14.8 dB but when used with a 12 Ohm load = -16.6 dB
              The output R of this combo = 2.7 Ohm
              R load = 17.6 Ohm (thus > 16 Ohm)

              3.3//1.5 + 15 results in: -23.8 dB but when used with a 12 Ohm load = -24.5 dB
              The output R of this combo = 0.95 Ohm
              R load = 16.something Ohm (thus > 16 Ohm)

              The 33 Ohm is used for the balanced circuit and is probably connected instead of the 15 Ohm and the common is disconnected.

              • Hsdw says:

                Sorry for the annoyance.
                “”3.3//1.5 + 15 results in: -23.8 dB but when used with a 12 Ohm load = -24.5 dB””
                this means something like this? https://imgur.com/a/kPMxmmx

                • Solderdude says:

                  exactly… the 3.3//1.5 (means 3.3 in parallel to 1.5) = 1 Ohm so the parallel resistors can be replaced by an 1 Ohm resistor when you want the exact same attenuation.

                  • Hsdw says:

                    Made 15 + 1.0 with 0805 smd in minijack housing, to avoid breakage i used short wires.
                    +- the same as iematch, thanks for help!
                    And the last question, about source output impedance and cables. I measured cables more carefully, and got 1.1 ohm signal + 1.1 ohm ground on the first, and 0.4 signal and 0.3 ground on second. So one сhain on first cable is 2.2 ohm , and 0.7 on the second. To equalize them i need to put 1.5 ohm resistor on the signal wires of the second? Or i just need to switch iematch to the lower mode (ultra 1.0 -> high 2.5)?.

                    • Solderdude says:

                      The problem with measuring low resistance values is the meter and its wires imparting relative big portions.
                      The best way of accurately measuring the resistance is to insert a DC current with a known value (say 0.1A or 1A) and measure the DC voltage across the wire and calculate the resistance

  27. Mick says:

    Hi Solderdude,
    After some advice please.

    I have already made this attenuator and it works great in most cases.
    I’ve placed the resistors at the plug end of an extension box which goes from the PC sound card to a boxed socket on my desk in which I plug various head phones. Obviously all attenuated by 20db’s.
    This is not ideal as some of the head phones I have do not need any attenuation.

    You state above that the resistors must be at the amp end due to the resistance of the cable otherwise will cause problems.

    If I use a really thick extension cable ( 3x 20AWG ) which measures less than 0.1 Ohm measured with my meter ( zero the leads then measure the cable )
    Then I could put the attenuators in the plugs of the headphones which require it.

    Would this work and not cause problems.
    To my mind it should do, but am I missing something.

    Thanks

    • Solderdude says:

      It should not be a problem I think. the 0.1 Ohm is just a -44dB worsening of stereo separation
      You can try it by putting a signal on the left channel only and then listen to the right channel and see how loud the signal is in that one.

  28. Mick says:

    Thank for the reply.

    So even such a small amount of resistance could cause problems.
    I make my own cables from several strands of 40AWG resin coated wire. (16 strands of 40AWG is equivalent to 20 AWG over all)
    So my best bet of success is to keep the extension as short as possibly needed and go overboard with the strand count to keep the resistance as minimal as possible.
    There is also resistance introduced by the connections as well I suppose….

    hmm….

  29. Mick says:

    made a new cable, reduced length and 32 strands of 33 AWG wire which equals 18 AWG overall.
    My meter only reads down to 0.1 Ohm and this cable zeros out so what the actual resistance is I dont know.
    When playing just one channel I hear absolutely nothing in the opposite ear, even at full volume.
    It works and sounds as it did before, except now I have a separate attenuator I can plug in when needed.
    Thanks for the help

  30. Mick says:

    Above its 16 strands of 33AWG (Not 40) equals 20AWG over all

    • Solderdude says:

      Indeed the wires should be as short as possible.
      Also the wiring of the common (ground) in the amp itself can be a problem with some designs.

  31. Mick says:

    Hi
    Just as a matter of interest how did you calculate the worsening of the stereo image ?

    I’ve managed to calculate the exact-ish resistance of the cable I made and just wondered how its worked out.
    1 strand of the wire 1m long is 0.7 Ohm so 32 lengths of wire according to a parallel resistor calculation is 0.0218 Ohm

    • Solderdude says:

      The calculation I made was incorrect to begin with and I forgot to include the attenuation the bigger resistor makes so the -30dB would be -44dB crosstalk.
      I should also have mentioned that it widens the stereo image and does not make it smaller.
      This is because monaural signals will be in counter-phase and thus is attenuated -44dB (0.6%)
      With 0.02 Ohm as the common wire you will end up with -57dB (0.14%) crosstalk.
      This you would only hear faintly when one channel is completely silent and the other one was playing at levels around 90dB (which is loud).
      Such channel separation is maybe only heard in some very left/right music such as early beatles recordings.
      Not something to worry about at all.

      The calculation is basically voltage division of the 0.9 Ohm (1.0//12) and the common to ground resistor lead. These are in series and the current through the 0.9 Ohm thus also passes through the 0.02 Ohm which thus creates a voltage across it.
      That voltage thus also is present across the 0.9 Ohm + 15 Ohm of the other channel when there would be no signal and this leads to a voltage level which is then converted to dB’s

      • Mick says:

        Thanks for the explanation.
        But call me thick but I’m a little confused where you get the values 0.9 and 15 Ohms or what they relate to.

        But NM it was only curiosity anyway 🙂

        Thanks

        • Solderdude says:

          Ah… those values were from a previous discussion with Hsdw. The mentioned values were based on those resistor values.
          With 3.3 and 33 Ohm the mentioned values improve a bit more (a few dB)

  32. Jun says:

    Hi Solderdude,

    I have a few questions:

    1. How are you calculating the optimal R1 and R2 resistor values for tube amps vs solid state amps? I see you are using a L-pad attenuator. I found a few useful links:
    https://robrobinette.com/Android_Headphone_Calculator.htm
    and
    http://www.uneeda-audio.com/pads/ (From this, I see how you got your 15ohm value for balanced, which is R1 / 2.)

    I’m trying to come up with resistor values for the two amps I have:
    My tube amp is: “Little Dot MK VIII SE Fully Balanced amplifier”:
    https://www.littledot.net/forum/viewtopic.php?f=9&t=871&sid=078541988af2cafdf226204ea361b72b
    The spec only mentions:
    “Input Impedance: 50K ohms
    Pre-Amplifier Output Impedance: 600 ohms”
    I’m not sure if the headphone output impedance is also 600 ohm (since it’s a tube amp, but seems too high).

    My solid-state amp: “Topping DX7s DAC/Headphone balanced amplifier”
    Output impedance: Single ended = <10ohms , Balanced XLR = <20ohms

    My headphones are: Hifiman Edition X v2 with 25ohm impedance and Hifiman HE 4XX with 35 ohm impedance.

    Plugging your resistor values of 33ohm (15ohm for balanced) and 3.3 ohm seems optimal for the solid-state amp, but I'm not sure about the tube amp.

    2. I did further research and found out that you can calculate the output impedance of a vacuum tube by doing (1/transconductance)*1e6 = output impedance (ohms). But I want you to double check me on this though. If my tube amp uses the 12AT7 tube (the transconductance is around 4000), then the output impedance calculated is (1/4000)*1e6 = 250ohm output impedance on the amp.

    Plugging the input values into the headphone resistor network calculator above:
    Headphone Imp: 25 ohm
    Amp output Imp: 250 ohm
    R1: 33
    R2: 3.3
    This gives me the following result:
    Effective Speaker Load: 35.92 ohms
    Attenuation: 21.8 dB
    Effective Phone Impedance = 3.26 ohms (confused on this part, shouldn't this be the new effective output impedance from the amplifier instead?)

    Are the R1 and R2 values still good values to use for the tube amp? I'm just worried when you mentioned to Rob above that:
    "Remember, you can ONLY use this particular adapter with the Bravo V2 or say the Bravo Ocean (which is also 47 Ohm out).
    Similar tube amps can also use this particular adapter like the G1217 amps (on medium output R setting) or amps like the Xcan V1 and V2 (33 Ohm out)
    Do not use it on any other amps when unsure output its output resistance."
    and
    "Then you will be loading that amp with a 4 Ohm load (or something close to it)."

    I didn't fully understand what you said to him and how you calculated the 4 ohm load.

    I plugged values from 1 to 500 ohms back into the Amp output impedance of the calculator and the only thing that changed was the Eff Phone Impedance, only changing from 3.0 to 3.279 ohms, but the effective speaker load stayed the same at 37ohms.

    3. Also, when playing with different R1 and R2 values in the calculator, what are the constraints I need to keep in mind? For example, should the effective speaker load be greater than my headphone impedance, etc.? Or should the effective speaker load be greater than the amplifier's output impedance value?

    Much appreciated.

    Thank you,
    Jun

    • Solderdude says:

      The values are calculated for low output resistance amplifiers and specifically for driving high efficiency head/ear-phones from desktop amps designed to drive both low and high impedance headphones.

      Most of these amps do not have any issues driving 32 Ohm.
      As low impedance and sensitive IEM’s and headphones are usually low in impedance and can have wildly varying impedances it is important for the source resistance that will feed the ear/head-phone to be as low as possible.
      An attenuation of 20dB is usually enough to suppress noise and get a good volpot range.

      So the adapter is designed for this usage. Not for usage with high impedance tube amps that cannot provide enough current.

      Your headphones are: Hifiman Edition X v2 and Hifiman HE 4XX which are both not super efficient headphones and planars.
      For the Topping it seems an attenuator is not needed at all unless you hear audible noise when nothing is playing.

      The little dot is more problematic as it is designed for high impedance (>300 Ohm) headphones.
      This is a problem when using it with low impedance headphones.
      However, you are in luck as your headphones are planars and while not super efficient they aren’t HE-6 power hungry either. The Ed x plays well with just a few volts on it, the 4XX likes a bit more.
      Why are you in luck ? well… planars have a flat impedance so don’t care about output resistance. (damping is not electric so also not an issue)

      The LD is spec’d at 1W into 300 Ohm and delivers 17V at that power.
      In 600 Ohm it is spec’d at 2W which means 35V.
      Strangely enough there is another spec that states 60Vpp = 20V so where the 2W into 600 Ohm comes from is a mystery to me.
      In any case… let’s assume the 1W into 300 Ohm is correct this means about 55mA of output current is available.
      In 25 Ohm this is 1.4V = 110dB peak levels which is quite loud.
      For the HE4xx 1.9V is possible = 112dB peak.

      To load the amp with 300 Ohm a 270 Ohm series resistor (R1) is needed, R2 is the headphone itself.
      The amp will see 300 Ohm and is happy and the Ed X will receive 0.085x 17V = 1.4V
      With the HE4xx the output voltage will be 0.115x 17V = 1.95V

      So all you need is a 270 Ohm resistor in series with the headphone in order to use the LD as intended.
      LD happy, headphones happy, you happy.

      • Jun says:

        Thank you very much!

        More questions:
        1. How did you calculate the 110dB peak level with the 25ohm and 1.4V? And likewise for the 112dB value.

        2. How about for balanced configuration? It seems you would need another resistor to bridge the “+” and “-” signals.

        3. If I build the 270 ohm adapter (above method) and have R2=25ohm (headphone), will it still be usable on the Topping’s amp with 10ohm output impedance? And same for a balanced setup that you will propose for #2, will it be usable with Topping’s 20ohm output impedance for balanced?

        Thanks

        • Solderdude says:

          1: I calculated the current at 1W in 300 Ohm -> calculated the voltage belonging with that current in 25 Ohm resp 35 Ohm (all Ohms law) -> looked up the specs on my HE400i and Ed X pages and used the dB/V value.
          Calculated the dB difference between 1.4 and 1 (resp 1.9 and 1) and added those dB’s to the values of the headphones @ 1V…
          Now those are undistorted peak values in RMS. When you are listening to material with a DR rating of 10 the average SPL that sounds undistorted will be around 100dB which is VERY loud.
          On DR rated material of 20 the average SPL will be 90dB which is still quite loud.
          The power rating of the resistor should be between 1W and 3W.

          2: for balanced it stays the same. The only difference between balanced and single ended is that the return wire is not shared.

          3: The 270 Ohm adapter is ONLY for this tube amp. For other tube amps the attenuation will be too big and is not usable for most dynamic headphones either.
          ONLY for these 2 planars and this particular amp.
          It must be removed when using the topping which should be connected directly (not via resistors)

          • Jun says:

            Thanks again for the clarification.

            Regarding the balanced setup. I see what you mean now. I was thinking of using R1=270/2 for each differential line (4 resistors total). But realized the headphone driver is now R2, so the setup is still the same in series and I would just use two 270 ohm 3W resistors instead.

            Switching drivers type now. I’m guessing there’s not a proper resistor configuration for using IEM dynamic driver earphones (16-24ohms impedance) with the LD tube amp and without changing its tonal characteristics. Just trying 330ohm R1 and 3.3ohm R2, creates a 40dB attenuation (which is too big). I probably should just make the 33/3.3 adapter for the Topping amp on my IEMs and forego the tube amp.

            • Solderdude says:

              The 270 Ohm is in series with the driver so it does not matter whether or not you use 2×135 Ohm in series or 1x 270, in both cases the resistance is 270 Ohm.
              So you just need 1x 270 Ohm per channel.

              Indeed there is no good way to use sensitive IEM’s and drive them from a low impedance unless when using a transformer which limits bandwidth.

              Yes, 2 adapters. 1x 33/3.3 for Topping and IEM and 270 Ohm for planars on LD.

              • Jun says:

                Hi Frans,

                I used the following technique to measure the output impedance of both the Topping and Littledot amplifiers.


                http://www.qsl.net/w/w2aew//youtube/How_to_measure_output_impedance.pdf

                I used this sine wave tone generator online to output the signal at 100Hz:
                http://www.szynalski.com/tone-generator/

                I have R1 = 298.4 ohms and R2 = 149.5 ohms, swapping between the two resistor loads, measuring V1 and V2, and then calculating Ro.

                When I measured the voltages for Topping’s V1 and V2,
                I get V1 = 4.99V and V2 = 4.83V
                This results with an impedance, Z = 10.266 ohms (Which is what I expected from Topping’s website specs)

                Then I measured the voltages for Littledot’s Tube amp’s V1 and V2,
                I get V1 = 1.056V and V2 = 1.049V
                This results with an impedance, Z = 2.0154 ohms!

                I’m very surprised and did not expect it to have such a low impedance value for this tube amp at all! I was thinking it would be 200-300 ohms.

                What does this mean? Do you think there are further circuitry that is lowering the output impedance (maybe an internal resistor network or op-amp at the output)?

                Would like to hear your thoughts on this. Since the output impedance of the tube amp is 2ohms, then that means I only need to build the 33/3.3 adapter to use on either amps. 🙂

                • Solderdude says:

                  There is a little snag here that isn’t clear because of the used values and voltages.

                  Will set you up with 3 tests you can do in succession which may show you what’s going on here.

                  You can repeat the test but now with an ‘open’ voltage measurement (so without any load) and once with a load of say 33 Ohm.
                  Set the open output voltage to 1V .
                  Attach the 33 Ohm load.
                  Measure again (cheaper multimeters will give incorrect readings, when your meter has a 200mV AC measuring capability it should read correct, when the lowest AC range is 10V or so the meter will give erroneous values)
                  When you do this I expect the topping to provide 0.75V (close to it)
                  The LD will drop to just under 1V most likely.

                  You must repeat the test but now with an ‘open’ voltage of 5V.
                  When you do this I expect the topping to provide 3.84V (or close to it)
                  The LD will drop to around 1.8V.

                  However, when you set the Topping to 10V out and load it the voltage will be around 7.5V theoretically unless it is clipping in voltage or current.
                  The resistor will get HOT !
                  Do this with the LD and expect the output voltage to be around 1.8V again.

                  Dynamic output impedance of an amp can be low but the LD is severly current limited. Because of this it can only drive high impedance loads.
                  150 and 300 Ohm are high impedance.
                  It cannot drive low impedance loads as it will be current limited so the 33 Ohm load adapter will cause the output stage to clip resulting in poor sound quality.
                  The measurements above will give a constant output R for the Topping and a varying output R value for the LD as one would watch voltages only. The secret here is current limiting.

                  So Topping feels fine with 33 Ohm load, LD with 300 Ohm load but possibly also with 150 Ohm load it seems.
                  But that may only be true for a 5V output voltage and not be valid at 10V for instance.

                  • Jun says:

                    Hi,

                    I went ahead and did the measurements and see that only the Littledot can do the ‘open’ voltage measurement. The topping outputs 0V when opened, therefore it has to use the two different resistor load technique.

                    But here are the results for Littledot, I went ahead and use all 3 resistor values:
                    R1 398.6 ohms
                    R2 149.5 ohms
                    R3 32.9 ohms

                    L-channel R-channel
                    Vopen 0.529v 0.562v
                    V1 0.526v 0.558v
                    V2 0.521v 0.553v
                    V3 0.493v 0.521v
                    Z1 2.27338403 2.85734767
                    Z2 2.295585413 2.433092224
                    Z3 2.402434077 2.589059501

                    L-channel R-channel
                    Vopen 1v 1.047v
                    V1 0.995v 1.04v
                    V2 0.988v 1.033v
                    V3 0.938v 0.974v
                    Z1 2.003015075 2.682884615
                    Z2 1.815789474 2.026137464
                    Z3 2.174626866 2.465811088

                    L-channel R-channel
                    Vopen 5.01v 3.93v (right channel seem to have less voltage at this range)
                    V1 4.95v 3.9v
                    V2 4.89v 3.86v
                    V3 2.645v 2.6v
                    Z1 4.831515152 3.066153846
                    Z2 3.668711656 2.711139896
                    Z3 29.41720227 16.82961538

                    Max pot location can only reach 6.3V, so I stopped the experiment at 5V

                    And here is the two-resistor load technique for Topping:
                    R1 298.7 ohms
                    R2 149.5 ohms

                    Topping L-channel R-channel
                    V1 6.58 6.51
                    V2 6.37 6.29
                    Z 10.21512205 10.86032283

                    And another combination:
                    R1 149.5 ohms
                    R2 33 ohms

                    Topping L-channel R-channel
                    V1 3.217 3.29
                    V2 2.619 2.682
                    Z 88.75612016 87.93331903
                    (Strange how the impedance went up with this load combo)

                    • Solderdude says:

                      Looked at the DX7 specs in first instance. the DX7s is a lower power version.

                      The LD seems to be able to deliver 80mA into 32 Ohm but will be clipping there. Most likely the output will be close to a squarewave skewing the measured voltage perhaps.
                      Did you use a scope or just a meter ?

                      The Topping specs are a bit weird. 78mW into 300 Ohm (close to max output voltage) = 4.8V with Max voltage = 18.7Vpp @ 300Ω = 6.6V but with substantial distortion.

                      345mW @ 32Ω = 3.3V with low THD and 13.3Vpp @ 32Ω = 4.7V with substantial distortion.
                      This would mean the amp can only deliver 100mA.
                      On Massdrop they claim 1,000 mW @32 ohms = 5.6V but judging from the measurements the 345mW is more likely. Your measurements suggest 2.6V so 200mW.

                      This is hardly more than the LD ! and explains why it appears to be clipping around the same voltage and thus the R out appears to increase while it is simply current limiting (clipping)

                      Still, I do not recommend to load the LD with anything below 150 Ohm so a 270 Ohm series resistor is still recommend but if you want it to play a bit louder the 150 Ohm may just add a dB or so.

                      The topping simply can’t deliver much more power into 32 Ohm it seems, or you measured opposite ground in which case the actual output voltage = 5.2V = 845mW close to the Massdrop spec.

  33. Jun says:

    I really should get an oscilloscope, I only have a Fluke 77 meter at the moment. Thank you again for your recommendation, I’ll make a 150+ ohm adapter for the LD then. As for the topping, you think I should also use 150+ ohms instead of the 33/3 ? If I use 150 ohms and 3 ohms combo, it’s a -35 dB attenuation. It would be nice if I can use 150/3 combo for either amps.

    • Solderdude says:

      The topping doesn’t have the needed voltage swing the LD has.
      You need 2 adapters.
      One to ensure the LD stays within its intended load and not load it directly with Planars.
      One to lower the Topping output voltage when using high efficiency IEM’s and get better travel on the volpot.
      The Planars should be connected directly to the balanced out of the Topping without any resistors.

  34. Currious Pixel says:

    Nice guide.

    Like to DIY even if I’m way over my head most of the time, that’s part of the fun.

    This is a typical Andromeda paring problem. Have HRT microstreamer which has 0.5 output impendance, and would like to bring it to just under 2.

    It would be nice if you could tell me what combination of resistors should I use, if that’s even possible with HRT microstreamer.

    Thx

    • Solderdude says:

      How much attenuation are you looking for ?
      If you don’t need attenuation (not plagued by hiss or a small usable volume control range) then only a small series resistor may be needed.
      The output resistance of the circuit, the load the amplifier ‘sees’ and attenuation needed will determine the resistor values.

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