I'm pretty much done tweaking mine. The only thing I'm entertaining at the moment is the dual OPA637 I ordered. If that works out, then great. If not, oh well. Well, done tweaking the amp anyway. I still see cause to upgrade my DAC. It's sort of a bandaid until I can afford better.
So far, here are my mods:
Mullard M8083 tubes: These are easily my favourite tubes, in conjunction with the op amp in use. Thing is, the current setup is compatible with every can I own. My Sony's bass don't go overboard, the Audio Technica gains bass, clarity, and warmth that it never had before (it completely transforms), my grados gain just a slight bit of warmth but don't lose anything, and My shures just sound plain neutral. The amp setup is just... good. I don't really know of a way to explain it other than it's probably another potential stock config that davidzhezhe should be investigating. It doesn't have any negative side affects with any cans I've tried with it and only seems to bring out the best in whatever's plugged into it.
Burr Brown OPA2107: A bit expensive but worth the money. Still looking at the OPA637 coming in the mail but if that falls through, it's really okay. What I got now is satisfying, but there's that part of me that wants the dual OPA637 to absolutely destroy the OPA2107. Fingers crossed!
Peek HAL-O tube dampers (7): These are pretty good, and the results are clear. While I can't claim or disclaim audible differences in the way the output sound is, what I can tell you is it reduces microphonics by a great deal. I caught them onsale at 9.97 a piece, and that was a steal for what they do. Thing is, they help avoid that ringing noise you get if you tap your desk, or what have you. Placement is crucial from what I can tell, and each tube is different. It's like a witch hunt finding the spot, and a lot of smashing keys on my mechanical keyboard or tapping on my desk. I look like a retard setting these up, but the result is worth it, in that I get less vibration induced microphonics. At current pricing of 50$ a pair, I'd say it's the last upgrade you should be doing, but maybe before higher end interconnects at least that's the order I'm going through. What you need to figure out for yourselves is a) do you have that annoying ass ringing sound, and b) does it bother you enough to spend whatever herbie's asking? Just get the next upgrade in this list. Alternatively, and while I haven't tested this others have with good results: O rings. Apparently if you go to the autozone or what have you with your tube odds are you can walk out with some o rings that'll do the job. Find some that are just tight enough to put up a bit of a fight when putting 'em on. Remember, these are expensive light bulbs, and are fragile so you don't want the hulks death grip, just something that'll stiffen 'em up.
BBB Cork Coasters: These go a bit further and seem to knock out the last little bit of vibration based noise the dampers don't catch. Sum of the parts, I guess. I bought a pack of these to use as coasters. Luckily, 3 left after they got packed away... found them in my kitchen when hunting through my home for something to reduce vibration and man do they work for what I wanted 'em to do. Now my amp doesn't really misbehave no matter what I'm doing. I still get microphonics off the headphone cable moving around or when I touch the volume knob, but from what I can tell, this is unavoidable. Basically, 8$ for a pack, you get some nice coasters and some good anti-vibration cork for your kit. And in my experience and having a good way to test for it, I was able to eliminate the last bit of noise with these. Awesome (free to me since I had 'em) tweak.
Next step, and most likely the last: Blue jeans cables. I'm really satisfied with how I grew as an audiophile with this amp. It taught me key things to look at with tube amps, what to listen for when rolling tubes or testing cans, and many other things I can't even think of with this amp. I suppose I could still start replacing caps or something, but I'm not really up for it. If somebody ends up listing some more mods that have 100% improvements towards clarity or resolution I might.
Edited by Aynjell - 9/19/10 at 12:11am