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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

KT88 PP - Opus 5.0 or other?

Hey everyone,

I've been spending a few days browsing around and contemplating what I might do for my next project. So far, I've built a Mikael Abdelleh SE amp with KT88's and have tinkered with it a bit. I've also built several of the ESP solid-state amps (P3, P101, P127).

At this point, I've been pretty successful, extremely satisfied with the sound quality of my amps, and I'm looking for the next challenge. For the most part, I'm running efficient speakers, so I don't necessarily need more power from my next project. However, I like for every project to build upon what I've learned in the past and I guess I'm looking to build a sort of ultimate amp.

I know from a sound quality, stability, and cost, etc. perspective, I could build a very nice solid-state amp. However, I want the fiddle-factor and challenge of another tube amp. I also kind of like the size, power, and availability of KT88 tubes, which I've been using in my SE amp, so that's where I started my search, but I'm not glued to them 100%.

I want to learn, do some calculations, simulations, etc. on this project, so I want something that's not too easy, but I'm not trying to write a master thesis either. I don't want to buy PCB's for this project. I would like to have separate power supplies per channel and probably to build mono-block. Given efficient speakers, I don't see a need to go to PPP, unless there's a compelling reason (40-80W seems reasonable). I don't see a need to build another SE amp, seeing as I already have a lovely one. PP seems like the way to go and Mullard sounds more inherently stable than Williamson, so I gravitated in that direction in my search. I'm not a purest, I don't have to have triodes and I'm not afraid of silicon.

I found this project below and the concept is appealing to me. I see it as taking a good topology, applying the best upgrades of the time, including some MOSFET's and regulators, and using that to make a killer amp. As far as I can tell though, only a couple of these were built and reported on here, but I did see it recommended a couple times.

Opus 5.0 Schematic

So my questions are these:
1. Why haven't more of these been built? Sounds too much like a solid state amp? Too much silicon? Too complex? Too expensive? More power than needed?
2. Is there anyone else who has built these and what was your take on the amp?
3. Is there a more compelling project to start from, along the lines of my rambling above?
4. If this is the way to go, what to change/upgrade?

Thanks for reading and the feedback,

John