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Old 10th October 2007, 12:01 PM   #1
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Default Help me choose headphone amp design

I want to build a headphone amp that has excellent technical specs, but also has few "psychoblunders". I.e, even if they have no real effect on the sound, I don't want any electrolytics in the signal path. It must be class A. No opamps, even if they have no faults. Actually, the new National parts are still tempting me. It probably won't have silver wire and Teflon caps, but I won't rule it out. I also won't rule out tubes, as long as the design is OTL. I've never been comfortable with transformers. I'm wary of Cdom compensation, having seen bad results with it in the past. I want just the right amount of negative feedback- enough to do the job, but not enough such that the amp could be labeled "high negative feedback".

What would you build? SS or tube? Bipolar or MOSFET? Massively paralleled devices (I have bags of TO-5 devices and bigger bags of TO-90 devices)? I have a lot of small signal tubes, but few power tubes. How complex a front end? Regulated or unregulated power supply. What do you feel strongly about?

Note that my headphones are ok dynamics, no fancy electrostatics. DCR is 47 ohms, 0.17 mH @ 1kHz. I don't listen terribly loud, probably quiet by most peoples standards.
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Old 10th October 2007, 12:09 PM   #2
h_a is offline h_a  Europe
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What about the Cavalli-KumisaIII ?

Class A, Jfet input, Sziklai-output, fully complementary, all discrete, dc-coupled.

What more does one need ;-))

Haven't build mine yet, so unfortunately I cannot say anything about the sound.

All the best, Hannes

PS: forgot: it uses an opamp for the servo. But which servo doesn't? And without servo you have a ac-coupling cap at input.
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Old 10th October 2007, 12:21 PM   #3
00940 is offline 00940  Belgium
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http://headwize.com/projects/showfil...lmore3_prj.htm

The designer's requirements list was similar to yours.

It sounds very good, btw.
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Ben.
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Old 10th October 2007, 12:31 PM   #4
PMA is offline PMA  Europe
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A universal answer would say - try www.passdiy.com

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Old 10th October 2007, 12:32 PM   #5
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Quote:
Originally posted by 00940
http://headwize.com/projects/showfil...lmore3_prj.htm

The designer's requirements list was similar to yours.

It sounds very good, btw.
The design seems very good, as long as you can find the input dual FETs. The other design uses single FETs which seem to be available in the US.

The Gilmore's power supply design is better, even if the 2200uF capacitors are not quite recommended at the 3X7 regulators output. But a PS with those chips will sound much better than 7X15 types.
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Old 10th October 2007, 12:39 PM   #6
x-pro is offline x-pro  United Kingdom
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I found that one capacitor in a signal path could be better than many more active devices required to get rid of it. That was one of the reasons why I made this headphone amp few years ago:

http://www.ant-audio.co.uk/Theory/AN...0Amplifier.pdf

It is SE class A and the output FET could be changed to suit low- Ohm loads.

Here are the measurement results for the original version (BSP129 output):

http://www.ant-audio.co.uk/Data/Amber_0015.htm

And that for a version with FDN439N on the output.

http://www.ant-audio.co.uk/Data/Ruby02.htm

THD measurements done at 500 mV RMS output (-8dB on the graphs) - it is very loud on most headphones.

It is a simple circuit that gives a very good performance thought it requires a careful selection and matching of transistors. To my ear it sounds better than most (but I would say that, woudn't I? )

Alex
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Old 10th October 2007, 12:48 PM   #7
PMA is offline PMA  Europe
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Quote:
Originally posted by x-pro
I found that one capacitor in a signal path could be better than many more active devices required to get rid of it. That was one of the reasons why I made this headphone amp few years ago:

http://www.ant-audio.co.uk/Theory/AN...0Amplifier.pdf

It is SE class A and the output FET could be changed to suit low- Ohm loads.

Alex,

now I understand. We have very, very different circuit, distortion and sound tastes.

Regards,
Pavel
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Old 10th October 2007, 12:52 PM   #8
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Quote:
Originally posted by x-pro
I found that one capacitor in a signal path could be better than many more active devices required to get rid of it.
Some will also say that the best cap is no cap at all, and for that you have to use more active devices. At least to make it symetric.

You could try that same design of yours bridged in mono, with no output caps, and see how it sounds as compared with the caps. That should be much better than any measurements you can provide.
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Old 10th October 2007, 01:07 PM   #9
x-pro is offline x-pro  United Kingdom
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Quote:
Originally posted by PMA
now I understand. We have very, very different circuit, distortion and sound tastes.
I think you would be wrong to draw that conclusion from this particular circuit. Headphone amplifier requirements are very different to what you need from a power amp to drive loudspeakers. I prefer low distortion and a very clean (but musical) sound. In this case most of the time distortion would be much lower than as measured - it is SE class A after all. At 0.5 V on the headphones your ears most likely would distort much more! All my power amp designs were AB with high NFB and low THD and I am happy with these too .


Quote:
Originally posted by carlmart


Some will also say that the best cap is no cap at all, and for that you have to use more active devices. At least to make it symetric.

You could try that same design of yours bridged in mono, with no output caps, and see how it sounds as compared with the caps. That should be much better than any measurements you can provide.
But not necessarily a better sound. I could easily improve measurements just by changing the load resistor in the output follower to a current source - and I 've tried it. However the sound was not as good - even at the levels where THD would be low anyway.

Alex
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Old 10th October 2007, 01:20 PM   #10
pilli is offline pilli  France
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...for what it's worth, here's "my" headphone amp:
(not much of mine, as you'll see )

I just use a "downsized" JLH.


All about the JLH can be found at
http://www.tcaas.btinternet.co.uk/

and then the idea to "downsize" I picked from the ESP pages:
http://sound.westhost.com/project70.htm


He proposes what is there called the "Headphone DoZ" amplifier (never found this name very polite...) (and DoZ is actually a variant of a JLH).


The JLH I made is the "no-caps" version, I think it's identified as "JLH 2003"; you'll find everything in the excellent site by Geoff Moss.


I used to plug the headphones on the "full JLH" for "test and debugging" purposes (most of it happens around midnight...)
of course through a "level reducer" (also inspired from ESP, basically some resistors - see project nr. 100).
Then I would just do all evening listening on headphones.
But all that heat was of course unnecessary, so I etched two more JLH cards, pulled some TIP35s from some old something, and there it is, a "low-power" JLH.
Just in case, I kept those resistors adapter. The level is just fine; voltage is +/- 18V and biased at 300mA.
Still massive heatsinks, but they were already attached behind the TIP35s



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