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needtubes 7th February 2004 03:51 PM

class A headphone amp (for high Z cans)
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Hi all-

I have been searching and searching... but cannot find what I am looking for. I would like to go tubes, but cost prohibits this. I can build a class A SS amp for much cheaper using good quality parts. The drawback, I suppose, is that I am using 300-ohm headphones and most class A headphone amps are designed with no voltage gain to be used with low impedence headphones (60-ohms or less). I do NOT want to use any opamps in this circuit. My favorite design is the Szekeres amp over at Headwize- ultra simple and said to sound quite good. The only problem is that is has slightly negative gain... and I would need a preamp in front of it to drive my headphones. Does anyone know of any class A headphone amps that will work well with high Z cans?

This is a really simple circuit I threw together to see what people thought... would this yield good sounding results?

Thanks for any and all help

Nisbeth 8th February 2004 04:39 PM

Build the Szekeres with a simple op-amp gain stage in front as described in the article:)


paulb 8th February 2004 07:43 PM


Originally posted by Nisbeth
Build the Szekeres with a simple op-amp gain stage in front as described in the article:)


You missed it, he doesn't want any opamps. Though I doubt you can get too much better than an OPA2134.
How about sticking the Zen input JFET circuit in front of a Szekeres?

joensd 8th February 2004 07:48 PM


How about sticking the Zen input JFET circuit in front of a Szekeres?
If you think of the FET in ZenV4, that is a buffer to up the input impedance and so wonīt get him some voltage gain.

What about Marcelloīs Zen headphone amp?
You probably have to change the gain a little but donīt need so much bias current.

Dragance007 9th February 2004 05:26 AM

Headphone amp
Recently i put together circuit on the link below. It sound very good.

protos 9th February 2004 10:10 AM

If you are using sennheisers or cans with suitable cords that can be terminated in balanced connection I would suggest what I am using: A Pass BLS with reduced voltage i.e. +-15V with 5 times the current bias (about 200ma per mosfet).You can use it single-ended as well but lose some benefits.You cannot get a much simpler class A circuit than that.It beats my PPA head amp in naturalness , staging and drive.You could just do it point to point.

Banfi T. 9th February 2004 11:53 AM


why the overall feedback? I suggest you the use of asymmetric differential configuration. Common base voltage amplifing in that configuration is much better than having a common emitter or cascoded stage. I built a circuit in this way from inexpensive BJTs and it surpassed everything I could lay my hand on. (The actual cirucit does not had a coupling capacitors and it was used also as a preamplifier...)


Nat Riscica 9th February 2004 12:40 PM

Hello Needtubes,

i use the Marcello's Zen with the HD 600 (300 Ohm) and he work great!. Really a very very good amplifier.

Nat Riscica

needtubes 9th February 2004 03:17 PM

Thanks to all for the replies.

I am currently using Sennheiser HD580s, which is why I needed voltage gain up front.

I had seriously considered the Pass BLS, but ruled it out because it used too high of voltage. What values did you use after you reduced the power supply rails? How low is DC offset on the output of that amp? I have been wanting to make a new cable for my 580s, so building this would serve two purposes. :rolleyes:

Marcello's Zen amp was also a choice, but I wasn't sure if it had the voltage drive for Sennheisers.

My preferred choice would be the BLS... especially since it can be adapted for use with lower voltage rails. One problem... I do not have any source that has balanced output. So, do I just hook the - input to ground? And then still attach the - output to my headphone ground? Any more specific info on how to do this would be much appreciated. :)

Thanks all

protos 9th February 2004 03:57 PM

I f you are really interested in the modified BLS I can give you all my info.By the way a balanced cable is no big deal just buy a spare Senn cable and modify it with two rca 's or four pin plug and then you can plug back to your original cable with the headph. jack if you need that type of connection.

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