Easy way to listen to power amp via headphones

Phisci · 30th March 2013, 09:12 PM

Hi guys, I would like to apply a few simple mods to my power amp (class a and also class d). If I connect say 20k resistor to the output of the power amp, would that allow me to safely listen to a 32R headphone?

JMFahey · 30th March 2013, 10:22 PM

You don't state the amp Power !!!!!

djoffe · 31st March 2013, 04:44 AM

There are two ways:

1. Simplest---2490 Ohm resistor in series with tip and
a second 2490 Ohm resistor in series with ring.
common ground to sleeve.

2. Better --- many folks cite the benefits of driving the headphones with a low impedance. Assuming a 50 Watt Amp (8 Ohms), then a voltage divider of 330 ohms feeding 4.7 Ohms is a pretty good compromise. It gives about a 4.7 Ohm output impedance, resulting in a damping factor of 6x with 32 Ohm phones.
If we assume 98 dB SPL at 1 mW with 32 Ohm phones, the 50 Watt amp would put an SPL into the phones of 100 dB SPL (jackhammer at 1 meter).

If your phones aren't quite so sensitive, you might have to drop the 330 Ohm resistor a bit...you just have to watch it, as even the 330 Ohm resistor dissipates 1.2 Watts with 50 Watts (20 Volts RMS) out of the amp.

Phisci · 31st March 2013, 05:39 AM

Thanks guys, the amps are 500w class D and 120w class A.
What would the recommended wattages be on the 330R and 4.7R be?

JMFahey · 31st March 2013, 07:45 AM

120W Class A?
Which amp is it?

Phisci · 31st March 2013, 08:01 AM

Krell ksa80

djoffe · 31st March 2013, 01:08 PM

330 Ohms, 2 Watts ok, unless you do a lot of full power testing on the amp for extended periods...in which case I'd use 5 Watts...

4.7 Ohms, a 1/4 watt resistor would be ok.

dfuhr7gm · 31st March 2013, 01:52 PM

hello,

may I suggest ESP's solution?

Headphone Adaptor for Power Amplifiers

JMFahey · 31st March 2013, 02:53 PM

330 Ohms, 2 Watts is fine for the 80W Class A amplifier.

Now, in a 500W amp, Class A or otherwise, you'll need a 15W one.

Why would anybody use headphones to listen to a 500W Class D amp is beyond me , though.

Or burn 400W dissipation, also to listen through headphones, same thing.

*Maybe*there's some reason none of them have headphone out .

jxdking · 31st March 2013, 09:55 PM

Another thing should be considered. The impedance of the headphone is not constant. It will change as frequency changes. If you just put a 330 in series to headphone, the frequency response might not be flat any more.
Head phone will be more like current driven if you put enough resistor to it. You will get different sound.

30th March 2013, 09:12 PM	#1
Phisci diyAudio Member Join Date: Aug 2012	Easy way to listen to power amp via headphones Hi guys, I would like to apply a few simple mods to my power amp (class a and also class d). If I connect say 20k resistor to the output of the power amp, would that allow me to safely listen to a 32R headphone?

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30th March 2013, 10:22 PM	#2
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	You don't state the amp Power !!!!!

31st March 2013, 05:39 AM	#4
Phisci diyAudio Member Join Date: Aug 2012	Thanks guys, the amps are 500w class D and 120w class A. What would the recommended wattages be on the 330R and 4.7R be?

31st March 2013, 07:45 AM	#5
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	120W Class A? Which amp is it?

31st March 2013, 08:01 AM	#6
Phisci diyAudio Member Join Date: Aug 2012	Krell ksa80

31st March 2013, 01:08 PM	#7
djoffe diyAudio Member Join Date: Oct 2008	330 Ohms, 2 Watts ok, unless you do a lot of full power testing on the amp for extended periods...in which case I'd use 5 Watts... 4.7 Ohms, a 1/4 watt resistor would be ok.

31st March 2013, 01:52 PM	#8
dfuhr7gm diyAudio Member Join Date: Feb 2012	hello, may I suggest ESP's solution? Headphone Adaptor for Power Amplifiers

31st March 2013, 02:53 PM	#9
JMFahey diyAudio Member Join Date: Mar 2009 Location: Buenos Aires - Argentina	330 Ohms, 2 Watts is fine for the 80W Class A amplifier. Now, in a 500W amp, Class A or otherwise, you'll need a 15W one. Why would anybody use headphones to listen to a 500W Class D amp is beyond me , though. Or burn 400W dissipation, also to listen through headphones, same thing. Maybethere's some reason none of them have headphone out .

31st March 2013, 09:55 PM	#10
jxdking diyAudio Member Join Date: Aug 2009	Another thing should be considered. The impedance of the headphone is not constant. It will change as frequency changes. If you just put a 330 in series to headphone, the frequency response might not be flat any more. Head phone will be more like current driven if you put enough resistor to it. You will get different sound.