New Headphone Amp

[Anthony Joseph]

I just finished my headphone amp that I have been contemplating since
I had you guys come over for a listen a while back. I could not use
the 26 tubes as they are a little noisy for headphone use and the
battery supply is not really realistic for a sale-able product.
Anyway, it is a OTA (One Tube Amp) not counting the rectifier tube of
course. It uses a Lundahl step-up transformer as the input stage and
an Emission Labs 20B tube for the output then to an Elecra-Print out
put transformer. It is pretty simple but to get it right took a lot of
time because the noise on a 300 ohm output tap is much higher than for
an 8 ohm tap. There are additional 32 and 75 ohm sockets at the rear
of the unit. I did not want them on the front as I will be using 300
ohm headphones and this will be my personal unit as well as a "show"
piece. I am planning to take it to the RMAF in October.
Let me know what you think.

Tony in Corrales

http://www.flickr.com/photos/45377567@N02/7323006382/in/photostream/

[Monte Verdi]

Congratulations, I know you've worked hard on this as I discussed it's
progress with you last winter! Can't wait too hear it, btw are there
any coupling caps and what is in power supply, and what is name?

Ramon

[Monte Verdi]

Okay, looked at internal photo and saw what is happening! Like the
look of those Clarity Cap soda cans and that chassis looks gorgeous,
good work!

[Anthony Joseph]

Hi Ramon,

Yeah, only 2 caps in the signal path. One is in the feedback loop, the other is the last power supply cap (the Clarity Cap). None are electrolytics! The Clarity Cap was a late change. I have been using the Mundorf M-Tube caps until the C-Caps came on the market. I had to try them and yes, they are better. The difference (in percent, not sound) is like the difference between BlackGates and the M-Tube caps. Clearer, cleaner, faster with more resolution but no added "grain". The prices are not too bad either. Well, at that level anyway.

Thanks for the compliment about the workmanship. It is essentially a prototype but it will be my personal amp and I needed to nail down the hours needed to build the unit for pricing purposes. It took about 42 hours to build. The internals are mounted on a sub-plate so as not to have the top plate of the amp look like Swiss cheese with over 30 fasteners to be seen. Top plate is .250", and the sub-plate and bottom are .187" aluminum. About $140 just in metal cost.

The circuit turned out to be simple but required a lot of work to get it right. It uses a standard RCLCLC power supply layout so no tricks there. I tried a tube driver stage but the differences between tubes was significant and the sound changed more than I liked. I wanted to have control of the amps' sound and not leave it up to "tube rollers" who would have opinions all over the map. The input tranny has just enough gain to make it work and it is way quieter than the tube driver anyway. It is an expensive option though at over $300 per pair. Actually by the time I built a proper driver stage not that much difference. By that I mean a voltage (tube) regulated CCS fed driver stage. It would have made the top of the unit much busier as well with 2 regulator tubes per channel and the driver tube to boot. The amp is already heavy at about 25 pounds. It is a beast. Lots of iron for that power supply and Jack Elliano at E-P does not seem to have any other frame size for his transformers but large and XL. Fine by me as they work incredibly well.

The modules you see are DIY-HIFI filament heaters. Very quiet and they work very well and keep noise and IM distortion very low. I have used them in my LadyDay amps for years now. . Not many options to add other than multiple inputs and maybe a silver input tranny made by Electra-Print (at about $700).

I have not come up with a name for the amp as yet but I think I will call the company "Exit Level Audio". I may call the amp "Annapurna" since the name means two things that I am shooting for with the amp. One is a high peak though not the highest as I do not want to "say" that this is the best. Gotta leave room for improvement! The other meaning is indicative of sustenance: http://en.wikipedia.org/wiki/Annapurna. Besides, it sounds mellifluous to me. Hey, maybe I HAVE spent too much time in the shop!

After some more break-in time we may want to have another meeting down here as we have discussed in the past.

Tony

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[Chris Woodward]

That looks great, Tony.  I look forward to hearing it.  Perhaps we can have another visit to scenic Corrales in the near future.

Chris