Mike
Didn't Colin order the Rev C boards from a different supplier for speed of delivery or cost. If so their QC may not be up to standard and from what you are saying Colin hasn't checked behind them. I think MikeCh and Marty need to get together by PM and see what is different in what they are hearing. Like you said earlier it could be bad boards or bad SI's. I had them in my cart and was about to pull the trigger now that Colin has put the price back to it's original point, but I would like to see where the problem lies first. It would seem to be a prudent thing for Colin to do if Marty contacted him about an issue to try and resolve it with another pair of boards instead of not acknowledging a possible problem. Could something have happened in shipping that would need the boards or Op Amps to need re-seating? I had Joe's Sparko boards for several weeks and they were fine.
I highly doubt there's anything wrong with the PCB's themselves. Basically Colin used a circuit design that was a quick and dirty fix that Richard from Sonic Imagery labs came up with. It was based on the original Hypex OEM board circuit, with a few mods to help stabilize his opamp, and filter noise. What Colin did was simply designed a board based on this circuit on a computer, sent the Gerber file to a PCB manufacturing facility, and ordered up a bunch of boards. Once they arrived, he soldered resistors, capacitors, connectors etc, onto the boards, plugged them into some power supplies and NC-500 modules, and simply listened to them. They sounded good to him so he just figured good enough, done deal. Well maybe they are good, and maybe not as good as they could be. Even if the circuit design is good, the resistors, cap types, and layout is critical. That's not the way things really should be done IMO. He should listen, then measure to make sure that nothing is wrong. If something looks off in the measurements, you simply need to go back to square 1. I have been urging him to provide measurements, but he said he isn't gonna do it.
Every amp should go through a QC stage, verifying that everything is perfect. As much as I believe the end user should trust their ears, the manufacturing end is another story. The AP machines make QC very easy. Just plug the amps into the machine, let it run the full gamut of automatic tests, and it will tell you if it passes or fails. If it passes, then put it in the box and ship to the customer. But the drawback is, the best ones like the APX-555 is $33000.
And yes anything is possible during shipping. But it's really easy to see if the opamp is fully seated.
So although I think Colin is doing a great job and offering great amps for a great price, he really needs to invest in measurement gear. Even a cheap Picoscope is better than nothing.
