Using spare power amp to power Headphones

dlaloum -- Fri, 10/23/2009 - 10:17

 Hi Folks
I have some spare good quality amps (quad 303, 405, 606) - would they provide a high quality alternative to a specialised Headphone amp?
Possibly using something like one of these units.. Furman HR-2, ProCo HJ4P etc... 
So basically spend $100 to connect my $2000 power amp to the headphones.... as an alternative to spending $200-$300 on a dedicated Headphone amp...
(Just exploring the possibilities... kicking tyres...)

Tom Martin -- Fri, 10/23/2009 - 16:13

One thing that has probably occured to you is that you have the power amps, so why not just try one?
The second thing to mention is that heaphone amps are generally very low power (1-2 watts into 8 ohms) and class A. I think you would want a class A or class AB power amp ideally. HP amps are designed for higher impedance loads, though I don't know of a reason these loads would be a problem for a power amp. Finally at very low power I don't know if some power amps would have noise problems, but they might. The overall point here is that you are using a device designed for one job (delivering significant current into a low impedance load) for another job. It might work, but why not just sell an amp and buy the device you need?

CEO and Editorial Director, Nextscreen LLC

dlaloum -- Sun, 10/25/2009 - 00:21

 That would make sense.... except the spare amp is the 303 which goes with my Quad ESL57's - which are currently in storage...
My Spare 606 is acting as a BiAmp amp with a second 606 running the rest, and the 405 runs the back channels (HT)
So I have 1 spare amp that I could leverage to do some HP listening and experiment - I can also experiment with the 303 and one of the 606's...
The 303 is a beautiful sounding pure class B - not currently a fashionable topology, and the 606/405 are all Quad current dumping amps... which I believe means a class A core with "current dumping" support...
My short list for HP's to consider includes the Beyer DT880 (due to experience years ago with the 80's version) - and the need for amplification for this beastie is what led me to think about this as an option.
But there don't seem to be many people out in Headphones land that have experimented with this type of option...


Tom Martin -- Mon, 10/26/2009 - 09:53

One final note: you may have a problem with overall gain (speculation alert goes here). I seem to remember that some integrated amps with headphone jacks, pad the HP output so that you can have reasonable volume settings (better control). What is your plan for volume control?
Ultimately the reason most people don't go down the path you suggest, I suspect, is that it creates all these issues. And, most people don't have spare power amps sitting around.
Let us know if you try it. I have a NAD 3020 integrated with an HP jack that I can try as well. It is lower power than the amps you are looking at.

CEO and Editorial Director, Nextscreen LLC

dlaloum -- Mon, 10/26/2009 - 11:29

 I remember the 3020 with great fondness - set one up for a friend years ago...
I will do the experiment in due course - it won't cost me much as I already have the amps, and it makes sense as I have no HP jack on my pre.... 
So my next step is to bite the bullet on a pair of HP's - currently lurking on e-bay to see what comes up
Melbourne, Australia has a dramatic lack of venues where one can listen to HP's and compare... so I will have to take a punt on something....
thanks and bye for now

strindl (not verified) -- Wed, 10/28/2009 - 20:52

I'm in somewhat the same boat as you with having some spare high quality power amps. I am currently using a Nelson Pass era Threshold S200 stasis amp to power a vintage pair of Stax SRX Mk III electrostatic headphones.   They are designed to be plugged  into their included separate adapter that in turns needs to be hooked to the speaker output terminals of a power amp. It sounds incredible even though those headphones are from about 1980 or so.
I'd love to be able to use that power amp to run standard headphones as well, like you want to do.  I just looked up that Furman HR-2 and it says it's desined for use with power amps of 50 watts per channel or less. That would be a problem with my Thresold which is a 100 watt per channel amp. 
Is there anything avaialble like that Furman HR-2 that would be suitable for a more powerful amp?

dlaloum -- Wed, 10/28/2009 - 21:05

 I think the amp power requirement is based on what will potentially damage the HP's ....
If you exercise a modicum of control.... then it is all dynamic headroom the way it should be!
I've run my Quad ESL57's with 100W amps into them.... without any damage... but if you crank things up too far... the stats give you a light show, and its time to take the panels to the (expensive) speaker doctor....
Some of the Quad 405's had a protection circuit that was set up to limit maximum voltage swing to protect ESL57's.... so it could still provide lots of current (for the 1ohm impedance the ESL57 drops down to) but didn't fry them.
I think the recommendations with all these adapters are similarly playing it safe.
In any case my first experiment is likely to be with the 30w RMS Quad 303.
The other interesting thing about the Furman - is it is designed to be daisy chained so a whole studio can share the feed - and they mention that with higher impedance phones it can support more phones... presumably a more powerful amp could handle more phones without strain....
I wonder whether they are set up in parallel (impedance would drop with more HP's) or serial (impedance would rise with more HP's
This would make an interesting review if someone wanted to loan a bunch of Furman HR units along with a swag of HP's
Also reviewing the difference between differing amps and HP's to see how this kind of setup really behaves in the real world
Anyone want to lend me a bunch of gear?

dlaloum -- Wed, 09/15/2010 - 05:25

by the way - the ART Headtap that I am using is spec'ed for a 50W amp same as the Furman HR-2 - I have it connected to my 140W Onkyo Receiver...

Just make sure you start with things turned right down - your head would explode way before the resistor network burnt out..... I simply cannot imagine (and don't want to!) what 50W coming through headphones would be like. (for the 1/2s before the headphones melt down...)

And it does work very well - totally exposes the sound signature of the amp

Mind you I am using 600ohm headphones - which is probably the most appropriate type for this kind of setup

PeterWillem (not verified) -- Thu, 11/12/2009 - 12:53

Why don't you take a Fubar 4-Plus from Firestone Audio. Very good, very nice priced ! If you want a class A, take a Cute Beyond form Firestone Audio.

dlaloum -- Wed, 09/15/2010 - 05:28

I've got a class A mod on the way for the Firestone Cute Curve - as well as a few opamps to experiment with and see what difference they make..

dlaloum -- Wed, 09/15/2010 - 05:21

 So this forum and the related amp/frequency response blog launched me on an Audio adventure....
(I've double posted this in both places...)

  1. I fleabayed myself a set of Vintage Revox 3100/Beyer DT880 Headphones
  2. I purchased an ART Headtap resistor network to connect to a speaker amp
  3. I ordered 2 dedicated Headphone amps to compare to (Firestone Cute Curve and Matrix M-Stage/Lehmann Black Cube Linear clone)

Once I had the Headphones (and had replaced the worn out pads - which took a while) - I started listening...

  • Onkyo TX-SR876 Receiver HP Jack (internal dedicated headphone amp) sounds good
  • ART Headtap connecter to Onkyo Speaker outs - Also sounds good
  • Cute Curve - Also sounds good
  • Cute Curve power by Creek OBH2 PSU - sounds BETTER

The Headtap ends up exposing the Amps distinctive signature much more obviously than speakers do. (and I prefer my Quad power amps over the Onkyo's internal amps)
So I have more testing to do... (the Matrix amp has yet to arrive)
So far with the resistor network (Headtap) in  place I have not noticed more noise from the speaker outs than from the dedicated headphone amp - results are actually very very good.... I just happen to prefer the Onkyo as a pre with my Quads - and the headtap exposes some of the aspects that I don't like of the Onkyo power amps.
So as an experiment it seems successful - maybe all power amp reviews should start with headphones connected.... they may expose the character of an amp better than many speakers.
Oh and by the way - hard to drive HP's will never be a problem with this approach!

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