Hi Frank,
I contacted someone that I knew was working on the UCD amps. With his permission, I am quoting from his message. I won't mention his name, because he wants to avoid the avalange of email. He put this whole thing in perspective better than I could.
"let me say I have the greatest respect for Frank VanAlstine. He has been one of the good ones, and a real asset to the music loving branch of audio. He has been consistent in offering good work for a fair price, from mods to products.
I have had no problems with the Hypex modules. We live in a radio bath, day in and day out. It isn't a problem if the levels are down far enough. Hypex uses around a thirty microhenry inductor I think, and the feedback is taken from after the filter. This solves the load interaction problem very well. Look at the frequency response with different impedance loads: It is almost identical. And on the question of load sensitivity, anyone who ever built atube amp with output transformers has already crossed that bridge. Last but not least, the proof is in the pudding. The Hypex comparator and output stage, when coupled with a really good input stage, is the cleanest and clearest amp I have ever heard. I think this is because of the low open-loop output impedance and residual distortion of the Hypex switcher. If you add a similarly good input circuit to make up the gain gap and provide a steady high input resistance, you will have a good amp. I know for a fact that Frank is more than capable of designing such an input
circuit. If my experience were limited to the first switchers I heard, I would avoid them too."
I only apologize that this other topic apparently got out of hand. Take
Raywhat you read here at face value.
