Just a quick note before turning in, the amps they are using are not A grade parts (selected for lower Vos & a couple of other specs, which wouldn't have an effect on the audio performance anyhow). Higher spec parts are typically not available in an SOIC package due to higher thermal stress in that package. Yes, it will sound better than a 741 or 324-style amplifier, which are still being used decades after their introduction. The point I was making was that they were charging over a C-note for an amp that anyone can go out & get for less and that there's nothing "esoteric" about a '627. I'm too tired at this point to go look up the specs, but is the 637 a decompensated '627? (I'm guessing the BB parts are DiFet or BiFet replacements for the old PMI/AD OP27/OP37 series) I could go on, but it would probably bore the few remaining lurkers to death... ;)

Merrell-

Yes, the OPA637 is an uncompensated 627. The point I was making is that even companies that sell multi-thousand dollar CD players, amps, etc generally use much less expensive opamps than even the OPA627, so in that sense it is not your run of the mill part.

For this reason, it's possible to modify these components for much better sound by replacing the lesser opamps with ones like the OPA627, and the capacitors with caps like Black Gates for relatively little outlay of cash.

The original point remains--$500 for a wood knob is highway robbery.