Convert power amps to headphone amps.

[bsas]

Is there a generic circuit that I could use to hear different kinds of power amps (tube or solid state, class A, AB or D) with headphones?

I found this project online:

Tube Headphone Adapter Box

DIY headphone adapter box for a vacuum tube amplifier.

www.skunkiedesigns.com

But I was wondering if there is a more generic circuit that could work with any kind of amp (on multiple wattages).

Thanks!

 

[raindance]

Putting large value series resistors into a headphone circuit may have negative effects on the frequency response of the headphones, meaning you won't get a true representation of how the amp sounds.

A lot of amps simply put a 330 ohm 5 watt resistors in series with each channel of the headphone jack. Same disadvantage as above sound wise, but you won't care about amplifier power.

 

[raindance]

Note that my suggestion cannot be used with tube amps, you'll need the circuit you attached.

 

[bsas]

Note that my suggestion cannot be used with tube amps, you'll need the circuit you attached.

Thanks! Can you explain me why I cannot use the circuit I attached for all kinds of amps?

If I understood well the circuit there is just 100 Ohm in series with the headphone and also there is an 8 ohm 25W to ground on both channels. First question is, if I plug a 50W class D amp is that going to fry the 25W resistor?

 

[raindance]

The resistor will only fry if you exceed it's wattage rating, which is determined by how loud you listen and the ratio between the resistors that determines how much power to "throw away". A 50 watt amp only outputs 50 watts when it's fed sufficient signal (full power), it's not a continuous thing.

The circuit you attached will work for most amps, but the attenuation it provides will be somewhat dependent on the headphone impedance used. You can always replace the 100 ohm resistor with, say, a 27 ohm resistor in series with a 1K potentiometer to allow some adjustment so that the 8 ohm resistor doesn't get too hot at the desired listening level.

What headphones do you plan to use?

 

[bsas]

The resistor will only fry if you exceed it's wattage rating, which is determined by how loud you listen and the ratio between the resistors that determines how much power to "throw away". A 50 watt amp only outputs 50 watts when it's fed sufficient signal (full power), it's not a continuous thing.

The circuit you attached will work for most amps, but the attenuation it provides will be somewhat dependent on the headphone impedance used. You can always replace the 100 ohm resistor with, say, a 27 ohm resistor in series with a 1K potentiometer to allow some adjustment so that the 8 ohm resistor doesn't get too hot at the desired listening level.

What headphones do you plan to use?

Here is the list of my personal favorites:

Koss KPH30i: 60 Ohms, 101 dB SPL
HD58X: 150 Ohms, 104 dB SPL
HD6XX: 300 Ohms, 103 dB SPL
HD560s: 120 Ohms, 110 dB SPL
HD579: 50 Ohms, 100 dB SPL
AKG K361: 32 Ohms, 114 dB
Grado SR80e: 32 Ohms, 99.8 dB SPL
Philips SHP9600: 32 Ohms, 101 dB SPL
ATH-M50x: 38 Ohms, 98 dB SPL

 

[pkane]

Is there a generic circuit that I could use to hear different kinds of power amps (tube or solid state, class A, AB or D) with headphones?

I found this project online:

Tube Headphone Adapter Box

DIY headphone adapter box for a vacuum tube amplifier.

www.skunkiedesigns.com

But I was wondering if there is a more generic circuit that could work with any kind of amp (on multiple wattages).

Thanks!

Depending on the sensitivity of your headphones, Hifiman sells such an adapter: https://hifiman.com/products/detail/84

Not for use with efficient headphones, as the high power output can damage them. Difficult, inefficient ones should work well (disclaimer: I've not tried the HE-Adapter myself)

 

[bsas]

Depending on the sensitivity of your headphones, Hifiman sells such an adapter: https://hifiman.com/products/detail/84

Not for use with efficient headphones, as the high power output can damage them. Difficult, inefficient ones should work well (disclaimer: I've not tried the HE-Adapter myself)

Where is the fun on buying something instead of soldering?

 

[pkane]

Where is the fun on buying something instead of soldering?

Just buy it, and then de-solder and modify

 

[aktiondan]

I went down this rabbit hole a couple of years ago, so I'll share what I learned, for good or bad. The main issue I ran into is you can't use regular unbalanced (3-pin/TRS) headphones and Class D without adding another pair or resistors to isolate the GNDs. Most Class D output topologies do not have a common GND, or rather the negative speaker terminals are not connected to each other (they are basically differential). If you try and connect a pair of TRS headphones in this manner it just shorts out the amp. In my situation I found that if you put at least 20 ohms between the negative terminals then the amp is happy, but this increases the load seen by the headphones, which can affect their frequency response and trashes the left/right channel isolation. Both issues were non-starters for me and I abandoned the project. If you use balanced headphones (4-pin) however, you won't have this issue and as far I can tell it could work.

I'll share what I put together just in case it's of use to you or anyone else. If you can get around the common GND and/or using balanced headphones dilemma, you'll still have the issue of the impedance seen by your headphones not being ideal (higher) which will affect different headphones differently. But I can say that I see the draw for this idea. I have an older Fiio A1 amp that I thought would make a great headphone amp. But after adding the extra resistors to the negative amplifier terminals and getting basically no channel isolation I figured it wasn't worth all the "extra watts" or "lower distortion" that made the original concept appealing the first place (or whatever anyone's reason might be for wanting to do this).

Note this calculator doesn't take into account if you have to add the extra GND buffer resistors which I didn't consider needing at first.

 

[raindance]

@aktiondan - excellent post, I didn't even consider differential or bridged amps in my response.

My personal opinion is that it's pretty darn cheap to get a decent headphone amp with low output impedance and switchable sensitivity, and easier than all this faffing about to try to hear the "character" of a speaker amp when potentially compromised by an attenuator of some kind. If you need character, add EQ.

 

[bsas]

I went down this rabbit hole a couple of years ago, so I'll share what I learned, for good or bad. The main issue I ran into is you can't use regular unbalanced (3-pin/TRS) headphones and Class D without adding another pair or resistors to isolate the GNDs. Most Class D output topologies do not have a common GND, or rather the negative speaker terminals are not connected to each other (they are basically differential). If you try and connect a pair of TRS headphones in this manner it just shorts out the amp. In my situation I found that if you put at least 20 ohms between the negative terminals then the amp is happy, but this increases the load seen by the headphones, which can affect their frequency response and trashes the left/right channel isolation. Both issues were non-starters for me and I abandoned the project. If you use balanced headphones (4-pin) however, you won't have this issue and as far I can tell it could work.

I'll share what I put together just in case it's of use to you or anyone else. If you can get around the common GND and/or using balanced headphones dilemma, you'll still have the issue of the impedance seen by your headphones not being ideal (higher) which will affect different headphones differently. But I can say that I see the draw for this idea. I have an older Fiio A1 amp that I thought would make a great headphone amp. But after adding the extra resistors to the negative amplifier terminals and getting basically no channel isolation I figured it wasn't worth all the "extra watts" or "lower distortion" that made the original concept appealing the first place (or whatever anyone's reason might be for wanting to do this).

View attachment 174173
View attachment 174178
View attachment 174174
View attachment 174185
Note this calculator doesn't take into account if you have to add the extra GND buffer resistors which I didn't consider needing at first.
View attachment 174183

Thanks a lot, that is exactly what I was looking for.

 

[Andersonix]

from solderdude himself!

Power amp adapter

home back to Learn 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) head…

diyaudioheaven.wordpress.com

 

[ZzZzZ]

So this He-adapter is a readymade solution for using speaker taps of power amplifier with headphones ? Hifiman site says "HE-Adapter is a device to protect amplifiers and headphones when using a speaker amplifier to drive HE6se, HE5LE, and HE4 headphones.

HE-Adapter is not for any high or average efficiency headphones.".

HE-Adapter

<p><strong style="font-size: medium;">Overview:</strong></p> <p><span style="font-size: medium;">HE-Adapter is a device to protect amplifiers and headphones when using a speaker amplifier to drive HE6se, HE5LE, and HE4 headphones.</span></p> <p><span st

store.hifiman.com

so could He-adapter be useful while connecting Susvara with 100wpc, class AB amplifier speaker taps (Burson Timekeeper 3IR) ?
What exactly this adapter do ?

 

[Andersonix]

Sounds like it's the circuit from #10 but with a slight difference in resistance.
If I were selling this to the unwashed masses I would also put a fat capacitor in line, or add a voltmeter to check for DC every time, as that can drift a lot on its own and normally doesn't settle until it's warm....

"Input: Speaker Connector
Output: 4 pin XLR
Resistors in Parallel: 10 Ohm
Resistors in Series: 25 Ohm"

 

[solderdude]

so could He-adapter be useful while connecting Susvara with 100wpc, class AB amplifier speaker taps

Yes. It will attenuate the output voltage a bit.