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.

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