My WN AUDIO headphone amp - line amp...

arco · « **on:** 17 Jun 2004, 02:29 pm »

Hi all,

I was in need of a good headphone amp when, somehow, I visited David's website. I am primarily a tube guy but when I saw all these goodies I said to myself that I should check these audiophile OP-AMPS and - why not - add a line stage to it, so I could drive my PLINIUS SA100 in an all ss based system. Some E-mails with David later, I decided to build a dual mono amp - preamp which you can see in its final form herebelow:

To do this kind of arrangement, I had to somehow modify the boards. Piece of cake after David sent me the necessary instructions. Then I decided, that I should have dual gain (0 and 14dB) at the flick of a switch...The main reason for this was that the preamp had to drive a 200WPC amp into my 104dB sensitive Klipschorns and still give me volume flexibility. Then the problems began, as it was impossible to make the necessary adjustments without having the preamp whistling and popping in a very annoying manner. Checked and rechecked everything (spending an awful lot of time, as you can understand...), until I discovered that one of the OPA 627's was faulty! Yep, it seems that things like this almost never happen, but my karma said otherwise!

David, again, was of much help as he sent me a new OP-AMP and, from then on, the performance of the finished preamp is near faultless, giving me a lot of pleasure (especially for the money spent...).

Nevertheless, this was a project it took me almost 7 months to complete, given the fact that I had to find a suitable chassis and also design and fabricate the front plate, among other things.

mgalusha · « **Reply #1 on:** 17 Jun 2004, 02:48 pm »

Very nice! It looks great. Did you fabricate the faceplate yourself? If so, it looks outstanding.

I like the flexible ground connections you have on the volume and selector shafts. I will have to implement something similar on my next project.

Mike G.

arco · « **Reply #2 on:** 17 Jun 2004, 04:22 pm »

Mike,

No, I have just designed the faceplate using a specialized software. Then, a CNC machine did the rest...

chrisallan · « **Reply #3 on:** 21 Jun 2004, 12:07 pm »

I've been considering a similar project myself. I have a nice relay-switched board from Avondale to handle the input switching and was looking for a circuit that uses OPA627s and probably BUF634s .
Can a headphone circuit be used for both duties - heaphone listening and as a pre-amp?

arco · « **Reply #4 on:** 21 Jun 2004, 12:24 pm »

Although the headphone and preamp boards are very similar, I don't really see how a single one of these could perform both duties in a competent way...Unless, maybe, if you use the dual gain function to good effect?

I believe DavidW should answer this one!

davidw · « **Reply #5 on:** 9 Jul 2004, 11:13 pm »

I've just been admiring Aristidis's pre/headphone amplifier - very professional - I really like the front panel. I had a look at the OPA627 that Aristidis sent back; it amplified ok but the crests of the waveforms were raddled with spurious oscillations. Obviously Burr Brown's product testing is less than comprehensive! Oddly enough a few days later I had another OPA627 from another batch that was completely dead. I've shipped hundreds of OPA627s but these two are the only faulty ones I've had - so far.
I guess that at some point Mike will share his experiences of using the LM6171 with the buffer/headphone amp. Its my favourite and Mike has come to a similar conclusion ( see his thread on headfi ). There's one small mod you have to make before the amp will work with the LM6171. You must remove R4 = 220R ( both channels ) and put a wire jumper, or zero ohm resistor, in its place. If you don't do this the amp will be unstable with LM6171s. You should also make sure that the amp never sees an open load or you can get instability as well. There is a small circuit trick that biases the opamp into class A with a quiescent current of about 2mA. I'll post the details if anyone is interested.

Raj · « **Reply #6 on:** 10 Jul 2004, 02:51 pm »

David, can the mods be used on the buffer amp too? If so I would be interested, and also if one can use the lm6171's.........

By the way have you ever experimented with other opamps after the rail splitter on the pcb???

Thanks
Raja

davidw · « **Reply #7 on:** 30 Jul 2004, 06:56 pm »

All of the mods for the headphone amplifier can be used with the buffer amplifier too. I haven't really experimented much with the opamp in the rail splitter but I saw Raja's post on headfi where he reckoned that using an OPA627 in place of the stock TL071 made an improvement. I tried a LM6171 in this position to check that its stable - it is - but I didn't have time to listen to it. Another suggestion that I've had is to use a pair of buffer/headphone amp boards to make a stero pair of balanced buffer/headphone amplifiers. I haven't tried this but it should work well and sound better than the stock unbalanced version.

Chazzer · « **Reply #8 on:** 2 Aug 2004, 08:45 pm »

Yes David - I'd be really interested in your tip as to how to bias the opamps into class A. Perhaps you could pass the "trick". on.
Also I had to change the op amp in the rail splitter when I switched to AD 8610s (I for one consider them a considerable improvement over the OPA 627). The 8610s generated a faint but irritating high pitched metallic whine through my phones until I replaced the TL chip with an OPA 134 which I had available - this never manifested itself with the OPA 627 devices; all very odd and odder still was the fact that the sound stage seemed to open up by upgrading the rail splitter chip.

Chazzer · « **Reply #9 on:** 13 Sep 2004, 09:06 pm »

Ok I've sorted it.

mccormw · « **Reply #10 on:** 23 Sep 2004, 01:59 pm »

Aristidis I agree with the others you amp looks pretty cool, I love the way you casually mention that you used a CNC to do the front panel. My CNC machine is in my shed so I don't like to use it in the English winter

By the way can you tell me what mains filter you are using please.

Bill Mac

frederic · « **Reply #11 on:** 21 Nov 2005, 12:41 pm »

Hello,

I'm trying to contact David([email protected]) but my mails are always rejected.

Is there another email adress or another way to contact him ?

Thanks

Frederic

arco · « **Reply #12 on:** 21 Nov 2005, 02:41 pm »

Not that I now of, sorry...

mccormw · « **Reply #13 on:** 21 Nov 2005, 03:53 pm »

His website looks kinda strange too.

Bill Mac

Raj · « **Reply #14 on:** 21 Nov 2005, 04:40 pm »

Hi,

My messages seem to get through ok. I think David used to have a phone number, somewhere in the catalog, but I think this was time limited, from 7pm to 9pm, as he is busy.

Thanks
Raja