Here’s my worthless 2 cent contribution which I may have posted about previously. When Paul McGowen of PS Audio set out to make a world class amplifier (at a "reasonable" price) he built custom input stages coupled to I believe Hypex modules at the time (not the very top model since he was using his own input stage anyway) He was quite happy with his design and brought it to the late Arnie Nudell’s (founder of Infinity) sound room to play on his prototype new smaller IRS speakers. When compared to Arnie’s custom tube amp he had commissioned, Paul’s designs continued to fall flat compared to Arnie’s reference, try after try. I believe he finally told Paul if he wanted to build a world class amplifier he’d have to scrap the project and hire Bascomb King (of Constellation, Marantz, Infinity as well as a respected reviewer/measurement writer) to design the amp from scratch. The design he came up with was MOSFET class AB and Bascome’s design beat Arnie’s reference, (which he promptly sold to make room for a BHK.)
I think it’s amazing that Paul kept his public informed along each advance and setback over the years. The time I waited for the BHK line to be released was worth it,
The R&D on Class D may have helped later with their lower priced amps, and from what I’ve read they sound really good, but there is a reason the MOSFET amps exist as their flagships.
Incidentally, Paul was very anti tube and PS had never released a tube product. Bascom convinced him to at least listen to a tube input stage. It was agreed and even planned to release the BHK’s with two input options, one tube and one solid state, built on tube socket for easy switching. But once they auditioned the two designs, it wasn’t even worth releasing the solid state version, and PS Audio had its first tube product and achieved its goal to be a top contender in amps (especially the mono blocks, which were conceived as a convenience option with only 50 watts more, but who’s balanced design once rolled off the assembly line and heard for the very first time proved to reveal another level of sonics above the stereo version. Of the few people that have heard the BHK (I imagine the mono) versus the much more expensive and top reviewed Constellation, they preferred the BHK.
