I'll second what Scott F. said about John Hillig of Musical Concepts (and Musical Design). I've had 5 pieces that John has modified for me over the years (including a B&K EX442 amp, Hafler XL280 amp, and a Hegman Hapi 2 preamp). The performance of all of them improved noticeably and the prices he charged were really reasonable, well worth the cost sonically. Plus he turned them around quickly.
I've also had Stan Warren modify equipment for me, and I've owned equipement from Frank Van Alstine. Along with John, each does excellent work. John and Frank have the quickest turnaround, though, and are the easiest to get a hold of when you have questions or want something done to your equipment.
For my serious listening I use an Ultra Platinum Hafler 220 that John built and a stock SP-2B preamp. I've run through quite a few expensive amps and preamps, first with a set of Gallo Nucleus References, then with my modified Newform Research 645 speakers, and the Ultra Platinum Hafler is the smoothest solid state amp I've listened to outside of the Ampzilla 200 monos (which I couldn't afford). The $1000 worth of Blackgate caps in the modded Hafler really makes it sweet and detailed. And the standard SP-2B preamp is surprisingly good for the money, too, especially when you use his interconnects and NOS tubes. One day I'll probably go for the upgrade to the signature or platinum editions.
John's equipment and modifications are really musical, without the glare, grain, and "hard" sound that too many solid state pieces have.
John doesn't get much press, which is too bad, because he's honest, does high quality work quickly, charges prices that are extremely fair, and is pleasant to talk to on the phone. He's been in business a long time, so he's clearly doing something right.
-M.
