Power amp adapter
published: Apr-5-2013, updated: Feb-09-2022
Can I use the speaker output terminals of a power amp to drive headphones ?
Yes and No….
Yes, because high impedance (> 300Ω) headphones can be connected directly to power amplifiers without damage
Yes, because some ortho-dynamic headphones need a lot of ‘power’ which can be delivered easily with power amplifiers.
Yes, when similar measures are taken as those found in most power amplifiers with a headphone socket.
No, because most low impedance headphones run a a high risk of being burned to a crisp when left unattended and the volume is accidentally turned up.
No, because of noise which could be higher than dedicated headphone amplifiers and could become audible.
No, When the amplifier used is of a so called ‘bridged’ design, such as a lot of class-D and car-audio amplifiers, unless 4 wire headphones are used.
So.. yes and no depending on the circumstances.
Below there is a lot of technical bla bla about powers and resistor values etc.
As most readers just want some info on a practical attenuation box for general purpose headphones you can skip most of what’s written below and go to the bottom of this page.There you will find how to connect a few resistors and what values you would need.
Amplifiers that drive headphones need to be able to deliver enough voltage to drive the headphones but not too much to fry them. Power amplifiers can deliver enough voltage. Since the impedances of headphones are higher than those of speakers headphones need less current so all power amplifiers have absolutely no problems to provide the needed current. Speakers in general have impedances between 4 and 8Ω, headphones between 32 and 300Ω.
Most speaker amplifiers can deliver between 15 and 300W depending on type and model. The numbers are generally given for impedances of 4Ω or 8Ω (sometimes even 2Ω or 16Ω) but these power levels will not be reached in headphones as the drawn power is determined by the output VOLTAGE of the amplifier and the load (IMPEDANCE), the higher the impedance, the lower the current at a given voltage.
NOTE: The section below is to show how headphones can be connected SAFELY to certain power amps (on the speaker connectors) so they won’t blow up.
If you want to know how much power your headphones can handle (NEVER connect earbuds and IEM’s to an amplifiers output !) you may find this info in this document
ALSO you should realise you NEVER have to reach SPL levels of over 120dB peak ! so when a headphone is rated 200mW it is most likely you will never drive it above 20mW in practice.
This also means that the values in the tables below MAY leave you little travel in your volpot. Sounding loud already when the volpot is barely turned away from its minimum setting. If that is the case (depends on the used headphone) simply calculate resistor values for max headphone power that is at least 10x lower than the max power rating.
SO… the power tables below are thus made to ensure you don’t blow up your headphone and NOT to reach loud levels at the end of the volpot range. You may have reached those levels already when the volpot has barely left the minimal setting.
Not everyone likes calculus so to make it more graphic by creating a few tables.
On the left column the specified power of an amplifier into 4Ω, one column to the right of it specified into 8Ω, next to it the output VOLTAGE that belongs to those powers and is the important thing here as the maximum voltage a headphone can handle depends on its impedance and power rating. It should be noted that most power amplifiers can deliver a HIGHER voltage in reality than the one given here because of the substantial load (4 – 8Ω speakers) the speakers provide is absent and thus the often unregulated internal power supply voltages do not drop allowing for a somewhat higher voltage swing.
On the next columns you can see which power can be achieved when the amp is turned up fully without reaching clipping levels. This is given for the most common headphone impedances. Green cells show the headphone with that specific impedance can be connected directly to the speaker terminals and will give no risk of drivers being damaged by too much power, the orange cells show the upper range of the power ratings of the most common headphones. the red cells show the headphones with these impedances should not be connected to the output terminals directly as there is a serious risk of drivers being burned/damaged/blown. This table is for headphones with power ratings ranging from 200mW (0.2W) to 500mW (0.5W). Most of the common headphones have these kind of power ratings, the smaller IEM’s may have power ratings of just a few mW so NONE of those should EVER be connected directly. When using these tables make sure you use the power ratings as specified by the manufacturer at the given impedance. A 50W amp specified at 8Ω delivers the same output voltage as a 100W/4Ω amplifier.
The table above shows it is no problem to connect high impedance (> 300Ω) directly to the output terminals of amplifiers capable of delivering 50W into 4Ω, Headphones with 600Ω can even be driven safely by 65W/4Ω power amps. Low impedance drivers, which are very common these days run a serious risk of being fried. A 32Ω headphone on a 40W/4Ω amplifier can receive 5W, way too much for drivers rated for just 0.2W.
The table below is similar BUT for headphones with power ratings between 1W and 3W. A lot of D.J.- and professional monitoring headphones can have (and may need) such power ratings as they are sometimes used as little speakers hanging around the neck or lying on a console while playing loud acting as small desktop speakers.
It is obvious the higher impedance headphones can be connected directly to amplifiers that can provide lots of power. The higher impedance headphones (>300Ω) can be connected to 100W amplifiers. The lower impedance headphones still run a risk when connected directly to amplifiers >20W. It should be noted these headphones would play incredibly loud at these powers and you couldn’t wear them on your ears but can use them as little speakers hanging around the neck.
Most of the newer Planar magnetic (Ortho dynamic) headphones can handle MUCH more power than normal headphones because of the way they are built. Most of them can be connected to power amps directly and will play beautifully on them. Headphones like the HiFiman HE5 and HE6 are best driven directly from power amps even. Below the table for 3W to 6W rated headphones.
It’s easy to see these headphones are not easily blown up but it should be noted most planar magnetic drivers are somewhere between 32Ω and 60Ω in general. This means these headphones can be connected directly to amplifiers up to 40W but I would not recommend to connect them directly to higher power amplifiers.
There is, however, a cheap and easy ‘fix’ so most headphones can be connected to power amplifiers but NOT directly. They can be connected via a resistor.
The bigger the output power of the amplifier the higher the output voltage and also the higher the added resistance needs to be. Below similar tables as above but this time with 3 different series resistances which are in effect the output resistance of the headphone output now (the amplifiers themselves are below 0.1Ω in general). The table below shows the output powers when connected DIRECTLY (so no added output resistor) to ‘normal’ headphones. Green is ‘safe’ to use, Orange is ‘safe to use when playing music’, Red shows a potential risk of frying these headphones. As you can see even low power amplifiers can potentially damage these headphones as the biggest part of the table is red.
The table below is for the same types of headphones (200mW) but with a series resistor of 120Ω (3W rating). It is obvious low power amplifiers cannot damage the headphones any more and even a 15W/4Ω amplifier can be used with music signals. The blue cells show these headphones may NOT play at substantial volume any more (depends on the used headphone).
Note: Because of the reduced output power the numbers in the table are in mW (milli-Watt)
Those resistors not only lower the output power rating but also the SOUND LEVEL.
The headphone will thus play a lot softer and some headphones may sound different as well.
Below a table that shows how much attenuation you can expect with different impedance headphones.
The table is made for 35Ω and 120Ω serie resistors.
Depending on the impedance variances of the headphone in question the frequency response may alter as well.
This is explained HERE.
When higher power amplifiers are to be used the resistor value can be increased. This is shown in the table below for a 330Ω (5W rated) series resistor.
More green areas so the resistor creates a bigger ‘safe to operate’ area and at the same time lowers the noise level of the amplifier (NOT the music signal). Amplifiers of 40W/4Ω can safely drive all ‘normal’ headphones and if we include the ortho dynamic headphones the whole table would be green.
For the sake of illustration below a table for a 680Ω (5W rated) series resistor. slightly more green but also more blue and not that much less red so increasing the resistance about 2 times (coming from 330Ω) didn’t do very much it seems.
The observant reader is seeing rather high output resistances. This is actually not something that is liked by a lot of headphones although some headphones could sound substantially more ‘Euphonic’ this way. Other headphones may become boomy and ‘fat’ sounding. To find out why read resistance, impedance and other issues.
Preferably the output resistance should remain below 120Ω although some headphones like the K701 for instance may sound a lot better from an amplifier with 330Ω or even 680Ω output resistance.
Voltage divider
The solution is to use a voltage divider that lowers the voltage. With this simple trick the output voltage of the amplifier is lowered by voltage division, similar to what is described above, BUT because 2 resistors are used we can lower the output resistance ‘seen’ by the headphone. This is because the 2 resistors not only divide the voltage so it is lower but also create a lower output resistance. The circuit is described above. R1 and R2 for both the left and right channel are mentioned in the tables further down on this page.
The reason for that is we can say the output resistance of the power amplifier is 0Ω (or negligibly close to it compared to the impedances and resistances that are connected). This effectively ‘parallels’ the two resistors that are used. The formula is simple. (1/R1) = (1/R2) = 1/Rout. The load the amplifier ‘sees’ is a bit lower as the R2 is in parallel to the impedance of the headphone. The load the amplifier sees = R1 + 1/ ((1/R2) + (1/Zheadphone)) and the output voltage of the circuit can thus be calculated as.
Uheadpone = U amplifier x 1/(((1/R2) + (1/Zheadphone)) / R1 + ((1/R2) + (1/Zheadphone))). It is obvious there are many variables including the differences in efficiency the possible outcome of calculations would be too much to fit in a few tables.
A factor 3 in voltage reduction = -10dB will be sufficient to protect and drive most headphones out there.
Then there is the question of noise.
Most power amplifiers are designed to drive rather insensitive speakers and noise is not an issue on speakers, unless you have your ear against the tweeters.
Headphones, however, are way more sensitive than speakers so the noise levels of a quiet speaker amp may become quite audible when not attenuated.
-10dB may not be enough to get rid of the noise or to get a decent adjustment range on the volume control. In this case it is likely the headphones will play quite loud already when the volpot is barely turned up.
The there is the question do we really need deafening levels when the volpot is at maximum setting ? Do we rather not need a usable volpot range ?
To get a better volpot range a reduction of 20dB (10x attenuation) may possibly be better though. Amplifier background noise will also be reduced by 20dB as well which may be needed.
So, I will make life easier and just will give some values that will yield a relatively low output resistance (below 10 Ohm) that will work on most power amplifiers (rated between 30W and 100W into 8 Ohm) and the majority of all ‘normal’ headphones out there.
The load resistance on the amplifier will be ‘light’ (about 35Ω) so the amp doesn’t need to work hard and won’t get hot.
R1 = 33Ω (5W)
For both the 10dB and the 20dB version R1 will be the same.
To have a about factor 3 reduction (-10dB) R2 needs to be 10Ω (3W to 5W).
The output R will be 7Ω which is low enough for most headphones.
To have about a factor 10 reduction (-20dB) R2 needs to be 3.9Ω (3W to 5W)
The output R will be 3.5Ω.
So there you have it.
R1 = 33Ω (5W) and R2 could have values between 10Ω and 3.9Ω (3W to 5W) depending on how much attenuation you want/need.
Thus buy 2x 33Ω, 2x 10Ω and 2x 3.9Ω for instance or values between them to try.
resistors don’t cost that much.
The box and connectors will define the build costs.
If you want to know how much power your headphones can handle (NEVER connect earbuds and IEM’s to an amplifiers output !) you may find this INFO in this PDF file
ALSO you should realise you NEVER have to reach SPL levels of over 120dB peak ! so when In case of doubt or other questions feel free to contact me (Solderdude) in this thread in our FORUM
BALANCED amplifiers (such as car audio or some class-D or class-T amplifiers) can NOT be used with headphones UNLESS the headphone is intended for balanced operation (4 wire/4-pin plug). When unsure do NOT connect the ground (-) connections of these amplifiers together. This may destroy the amplifier.
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.
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. Certainly NO problem when using a power amp to drive headphones.
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.
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.
The red (or +) connector of the amplifier must be connected to Right + (and for the left channel the Left + and the black (or -) connector of the amplifier must be connected to Right – (and for the left channel the Left –).
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 (by accidentally using a single ended headphone) the amplifier 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).
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.
So be careful with the TRRS jack.
Below a few possible pinnings of gear with a 4 pin TRRS jack connected.
As most of these aren’t specifically for headphones below a listing of the 4 main configurations of this TRRS plug.
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)
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 !).
The most common usage is balanced. This is standardized and all XLR sockets in (pro) 
audio 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.
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.
DIY-Audio-Heaven 
Hi Frans
Is the voltage divider update still going to be written? I have tried other sources but they all assume a little more initial knowledge than I possess.
Thanks, Syd
Yes, I still have to complete the article and had forgotten about it.
What’s missing is voltage divider networks and still have to figure out how to ‘present’ is due to the many variables involved.
The trick will be to maintain a defined output resistance and figure out how they are affected by the load and how to incorporate different voltage levels (power levels in 4/8 Ohm)
Had started on it a long time ago but other projects required more attention.
I do plan to complete the article though…
That’s great to know Frans. I look in this bit from time to time but finally decided to ask. This whole area is excellent but is it readily ‘discoverable’ to newcomers? I always go to Ian’s ‘Welcome’ post then on from there, or am I missing something?
Syd
Whenever I update or add something I make a note on the ‘home’ page.
https://diyaudioheaven.wordpress.com/
checking that page should tell you what has been added or updated.
Ah!, I’d forgotten about it being a separate area. I’ll add this to my daily checks.
Thanks Frans
Hello, great read. I have the AKG K240 Monitor (600 ohm). I have tried them on sound card that is rated to drive 600 ohm cans, on external usb sound card / mixer and some integrated stereo (speaker) amplifiers.
On both sound cards they sounded ok (interior one didn’t have much power), both lacking in bass.
On integrated amps: on one they also lacked bass, power was there (Denon PMA700V, 100wpc/8ohm).
On second amp they actually sound quite decent from hp out (JVC A-X2).
Interesting fact: external usb sound card/mixer and Denon integrated both had 120 ohm resistors in series with +L and +R out on headphones.
JVC on other hand has 220ohm resistors in series.
I am tempted to try adding some other values (higher) and check the sound then.
I’ve tested them on JVC speaker output terminals, there was loads of power, but stopped until i put some in line attenuators (at input).
This last thing i mentioned would imo be quite important addition to your truly great article: alot of people will probably test this on “old / vintage” integrateds.
These old devices have, in today’s money, rather high sensitivity on line inputs, let me write down these that i have, with year of manufacture:
JVC – 150mV (1979)
Denon – 150mV (1986).
My interior sound card with HP amp also has output levels of 3.0V.
In this case volpot will be very sensitive and users might actually drive amplifer into clipping and bad distortion. So even power levels will remain same, square wave (clipped peaks at high power levels) could potentially make some damage.
I have fabricated -20 dB inline attenuators (simple two resistors, this link http://www.uneeda-audio.com/pads/ ). Thats still about 300mV, but i figured some music might be recorded not so loud (older music of course) so better to leave some “reserve” there.
Even on speakers my volpot on both amps was too sensitive. This did the trick perfectly.
My point is, attenuation for older amps might be needed not only on output, but on input too, as amp might reach it’s rated power output with volpot still in sight of -∞ mark.
Yep those are valid points when it comes to usable volume control range.
In-line attenuators can certainly help here but doesn’t change the maximum allowable power in the headphone which is what the article is about.
Your attenuators seem well designed and made and will certainly help when connecting modern DAC’s to old DIN and RCA inputs of vintage gears as the ‘line levels’ were much lower in those days.
When using an input attenuator of course the maximum output level will be determined by the gain of the amp and max output voltage of the source.
In case someone would use only an input attenuator to get the proper volume control range and connect headphones directly to speaker outputs one could still blow up the headphone when selecting another connected and not attenuated input for instance or might be hearing background noise from the amp with sensitive headphones.
A passive attenuator at the output lowers the amp noise relatively and prevents accidental overloads.
When the volume control range still is a bit small one could make a passive output attenuator with more attenuation or use your attenuators.
The power amp attenuator should never be connected to the headphone out connector of any amplifier and is intended for speaker terminals only.
You raised good points though and may incorporate them in the article as well to make it even more ‘universal’.
Ugh, i completely missed the fact about noise floor going down with attenuator(s). Indeed, amp noise will go down in case of attenuator at output. So perhaps for vintages it’s just better to put more attenuation on output. Still, on one of my sound card outputs, there was tiny bit of characteristic noise noticable(some tiny interference from pc), well noticable if you stuffed your ear into tweeters at full volume with no signal(but sometimes we do silly things like that 🙂 ).
I understand your point perfectly, still some attenuation at input won’t do harm in lowering source device noise floor and my main point was, repeating, basically without having input at level amp was designed to “expect”, it is reaching it’s max rated output much earlier (relative to volpot position), rest past that point is just distortion.
Keep up the good work!
Hey Syd, I’ve made a TRS –> Banana adapter for my Hifiman HE-5’s (without any resistors) to specifically play with my NAD D 3020 30WPC (@ 8 ohms) speaker amp. I’ve connected the L/R to their respective poles on the female TRS lugs, and both grounds from the respective amp speaker outs are connected to a common-ground on the female TRS jack. Does this sound safe/correct to you?
Yep, perfectly O.K. for an HE5. Should you hear background noise or can only use the bottom part of the volpot range (unlikely as the efficiency is very low) then you can always add some resistors.
Cheers mate! Will report back.
The HE5(LE) is rated at 2W and the NAD can deliver 5W (non clipping sinewave) so take care you don’t turn it up all the way to see how loud it can go.
Distortion = ‘stop’.
5W peak power in real music usually means average power is below 0.5W.
It plays quite loud already in that case.
hi.
I have an EL34 tube amp, 8w. Probably balanced (negative ground not short circuit!). I would like to use single-ended headphones, then a female trs connector on the panel. which circuit should I use, with what attenuation? the headphones range from 32 to 250 ohms.
thank you
The output is most likely a transformer winding so can be used balanced and single ended.
In this case it is safe to connect the – outputs together.
When you want to make an attenuator I would use R1 = 15 Ohm and R2 = 1.5 Ohm and see if this gives you the range you want.
Dear Frans, that’s quite some good info, thanks for that! I have built a Stoetkit Junior ages ago which is a 9W UL push-pull integrated amp and has (i’m pretty sure) balanced outputs as it has separate transformers for L and R.
Not sure though if I understand your answer above: with this amp, can i now try and use ‘normal’ headphones (using a TRS connector)? And if so, should i then go for a balanced headphone amp attenuator? Your expert advice on this would be much appreciated (and some resistor values if possible). Many thanks in advance!
When you have a headphone that has a balanced cable and your amplifier has outputs where the – (or +) outputs do not have a connection between them, so fully separated you can use the balanced attenuator.
When your headphone only has a TRS connector then you can build the ‘normal’ attenuator and simply connect the – L & R outputs together to form the ‘common’ (sleeve) contact of the TRS plug.
Resistor values will depend on the balanced or regular attenuator being used.
Thanks a million Frans,
I was a bit hesitant for blowing up my valued tube amplifier which has balanced outputs. I indeed do not have balanced headphones so then I’ll just connect the — L and R outputs and build me a regular attenuator. Being a balanced 9W tube amp do you have any quick advice regarding resistor values or should I experiment a bit?
Thanks again,
Sander
You must be Dutch owning an old amp from Rik Stoet. Can’t find much info on it. Does it have more than one load impedance settings/choices ?
If not in what impedance is the 9W rating specified ?
It may be wise to use higher power and very low resistance value attenuator resistors that, when combined create a resistance close to the impedance the power is rated in (4, 8 or 16 Ohm for instance) because of the used transformer expecting a certain load.
Hi Frans,
yeah I’m Dutch alright, although i haven’t been living in the Netherlands for quite some years. No different settings possible and an impedance of 8 Ohm i believe the 9W is rated with. Is this enough info for you to have some tips re. R1 and R2 resistor values? Happy to share some brochures or construction manual incl. schematics if that’s of interest…
When loaded with 8 Ohm you will get 8.5V at 9W. With it you can drive high impedance headphones (300 Ohm) and most planars directly without the need to attenuate.
For lower impedance headphones (some of them are rated just 0.05W) attenuation is recommended as well as for usage with IEM’s .
So depending on the used headphone you could build an attenuator with R1 = 6.8 Ohm and R2 = 1.2 Ohm (R1 needs to be 10W) and leave that connected while listening to headphones.
You could build in a small switch (1A rated is enough) that lets you switch the headphone socket between the two end of the 6.8 Resistor. In one position high impedance headphones can be used in the other position sensitive headphones can be used.
For both situations the amplifier sees an 8 Ohm load.
The low impedance headphones see a 1 Ohm load resistance.
Brilliant – thanks a million! I will give this a try.
All the best!
Good day,
This is an informative article & many thanks for posting it.
I’m looking for an answer for a problem I’m facing currently.
I want to get an attenuated audio signal from the speaker outs of my music system.
Its model number is yamaha mcr-b142 with 15W output to 6 ohm load from each side.
It has bridged outputs, So it’s not easy to find a solution easily.
I’m going to use this attenuated signal to drive an arduino based spectrum analyzer.
This signal needs to be similar to signal coming out from earphone out.
please suggest me a proper solution to this issue.
Thank you very much.
You can do this by using a small output transformer or line transformer with a 1:4 ratio or something like that.
Another option is to use a capacitor to couple the + output and use the metal screen of the DAB antenna input as ground and use a small resistor divider to lower the output voltage.
Many Thanks for your reply.
I’ve came across this design & I’m planning to use that
Above design is for 75W into 8 ohms load.
I’ll be using same design with appropriate component values.(resistor value)
For the transformer, I’m using a 1:1 600ohm audio transformer bought from ebay.
Will this setup work as expected ?
Any risk involved in this method?
Thanks Again
R1 and R2 should be 1.8k, the output of the circuit must be loaded with about 600 Ohm (2x 1k2 in parallel)
That should give you 1V at max output power level.
I tried your schematic and when i turn volume up around 15 from 35 the speaker spurce cut output as that 3.9 Ohm resistance is to low and my system think it’s a short, I made 10k with 1k for speakers to line out and it works perfect but I need also for headphones as my system doesn’t have one. Thank you any way!
which schematic are you talking about ?
Hi, I´m using a Audio-Technica ATH-ADX 5000 on a JJ 322 SE Tube-Amp. The best Sound is available by cutting of the headphone-Jack and so get rid off the common ground by connecting the right and the left channel with +/- Outputs of the amp. I use al parallel 8,2 Ohm Mundorf resistor for each channel. Works realy great 🙂
Can a Crown DC300A Series II amp be used for a variety of phones rating from 50 to 280 Ohms safely. I would be the only one in this house trying this (no kids etc ). Or might you have a better suggestion? The DC300 is the only available amp not being used here. All others are commercial touring amps.
Thank you,
John
With a power adapter yes, It is kind of overkill and perhaps something like the Schiit Heresy or JDS Atom is an alternative.
Said amp can deliver a whopping 45V so needs a lot of attenuation to be on the safe side of things.
Hello,
Was reading through this and I was wondering if I can do the opposite, as in power speakers with a headphone amp via the 6.5mm jack(preferably without blowing up the amp). I have Hifiman EF5 which can supposedly output 15V @ 32 Ohms and can power headphones from 2Ohm to 2kOhm. The power input of the amp says AC 18V 50-60Hz MAX 1A and the PS input says 25W MAX. The speakers are either KEF Q150 8 Ohms (min.3.7 Ohm) 86 dB ( 2.83V @ 1 m ) or LS50 8 Ohms (min.3.7 Ohm) 85 dB ( 2.83V @ 1 m ). I am using them nearfield so I don’t need them to be too loud. Also if this would work do I just wire the speakers directly like a pair of headphones?
When you do not drive the speakers loud it will work. However the output stage might get a bit hot when driving the speakers a bit louder.
It won’t reach 15V on 4 Ohm speakers though as it would be pumping out 2x56W.
Perhaps it could safely deliver just under 2x 10W in speakers using music.
Could be less.
Tip = L + speaker
Ring = R + speaker
Sleeve = – L speaker and -R speaker connected together.
You can try it but need to lower the volume when it distorts or when the amp get’s too hot.
Before other people like to try this with their amps I strongly recommend against this as headphone amps are usually only designed to deliver low power, certainly in low impedances.
The current limiter will kick in and the output stages will dissipate a lot of power (thus heat)
I have a pair of Sennheiser HD558’s and I’m if I can hook them up to the amp I’m looking to buy. Sorry to trouble you fine folks but I have no clue what half of this page means, but if one of you can tell me that would be fantastic, here is the link to the amp, https://www.monoprice.com/Product?p_id=611815 if for some reason the link doesn’t work, it’s the Monoprice 15watt celestion
Hooking up the HD558 directly to the speaker will probably be noisy. Also you may not be able to turn up the volume and get the ‘tube sound’
You will need an attenuator between the speaker and headphone.
Would any male 1/4 to female 1/4 attenuator work?
The amp is a mono guitar amp… When it has a Jack output (cannot see on the pics) it is likely mono. In this case you need a TS (Tip-sleeve) connector to the amp and make it mono (TRS) for the headphone. It would have to be a special.
When it has a TRS out I don’t know how that will be wired.
[…] Source: Power amp adapter | DIY-Audio-Heaven […]
a few mW most likely.
I think the calculations for headphone power using the series resistors are wrong. That’s the power consumed by the resistor and the headphones together.
For example 120ohms resistor and 32Ohms headphones on a 6W power amplifier consume 0.158W, then the currently flowing though them is sqrt(0.158W152Ohm)=0.0322A. Headphones power = I^2xR =>0.0322^2×32=0.0332W= 33.2mW. The rest is consumed by the resistor 0.0322^2×120=0.1246W=124.6mW.
Or simply Power x (Resistance ratio) : 0.158W*(32/152)=0.0332W=33.2mW
and 158W*(120/152)=0.1246W=124.6mW
This is why using 300+ Ohms results is very low volume on the headphones
Good catch… there was an error in the formula. Will redo the tables. No one spotted this over the last 9 years.
Fixed now.
Great article, but I got a cruel doubt:
I have a amp (Technics SE-C01) which can deliver 40w RMS (8 ohm) per channel. It Has a headphone input.
In its manual says:
HEADPHONES OUTPUT LEVEL AND IMPEDANCE: 470mV / 330ohm.
I want to know if can plug the Hifi Sundara (37ohm, don’t know the max voltage it needs) in it. I’m afraid because i don’t now about headphone voltage and if this amp can handle it without damage.
Nobody else to ask for help. Hope you can help me.
The headphone out of your amp is 330 ohm (I checked the schematics) and when the Sundara is connected will give max 1.8V at max volume. Enough for 110dB SPL peak (around 90 dBA average).
The high output resistance of the amp is not a problem for the Sundara.
Hi!, I have 100 wpc Adcom GFA 545II and I am about to drive my Sennheiser HD 600 with it. Would 2x R1 value of 6ohm and 2x R2 value of 2 ohm be enough?
For HD600 I would use 68ohm (R1) and 39 ohm (R2)
R1 needs to be 2W rated. R2 can be 1W rated.
thanks for sharing!!! I had a valved pre amp from china (Fosi Audio P1) but these device don’t have headphones connectors. any clue how can I do that? any possibility to adapt your scheme to work with security ? thanks a lot and have a nice day 🙂
The output current the P1 can deliver is too low and the output resistance is too high to drive headphones. The only way would be to add a headphone amp.
Thanks a Lot . I think that o can find a circuit board on eliexpress . I took the sinal from the end of LINE and inject It on the input of the input of the headphone board . Nice . Thanks.a.lot for your attention . I Will lokking for a phone board to do It 🙂
I’m trying to attach a 3.5mm headphone Jack to a 4 screw speaker output on a cheap TDA7265 amp. But I’m getting no sound. All I hear is a pop when I turn off the 9V battery to the amp. The pop is louder when I have the pot turned to max, but no input sound is heard. The same pop is heard when the RCA plugged are removed. I’ll provide image if I get a response.
These outputs are most likely balanced. It shuts down because you are basically shorting 2 of the 4 outputs of that amplifier.
This is the amp Iâm using and how I have it wired up, if th
The chip itself is simple stereo. When 1 chip per channel is used (so there are 2 chips inside) the output is balanced.
When both – outputs on the amp are always connected (so 0 ohm) then the adapter should work. When you measure anything more than 0 or 1 ohm the output will be balanced. (when powered off)
Here is a link to the exact amp I bought on Amazon:
https://alexnld.com/product/tda7265-dual-channel-stereo-power-amplifier-board-25w-25w-pure-post-level-power-module/
It should be no problem connecting the attenuator with this circuit.
Does it work with speakers ?
An attenuator would be a resistor on the left and right channel of a headphone jack, wouldn’t it? It would be nice if I could share some pics, but not sure how to here. If someone could just Email me at [my name used here]@cox.net, this could go a lot faster. A picture is worth 1,000 words, as they say. 😀
I’m getting a stereo 3.5mm plug with three wire leads on Amazon. That will solve any issue with my Left/Right Phono plugs to volume pot rig… I’ll just have to control volume from the computer instead. I’ll test it that way. If it still doesn’t work, then I’ll attach one regular speaker to one channel of the speaker outputs. That should solve the headphone jack rig (if anything is wonky with that). If it still doesn’t work, then I’ll try attaching a small 12V battery to the power leads (why does it have a ground screw in the middle? Batteries don’t have a ground lead, like AC), in case the TDA7265 wants more power. Not sure why, but it’s the only other thing I can think of.