Speaking of the walwart power supply, I'm looking into alternatives. I'm not a big fan of blocky, outlet hogging converters, convenient as they are. I was looking into a different input source without by passing the the two 2200uf capacitor bank or voltage regulator. I was wanting something that is pretty much self-contained and found the Mean Well EPS-35-36 (http://www.meanwell.com/search/eps-35/default.htm). It has an adjustable output voltage of roughly 32 to 39 volts DC at 1A. I'd simply replace everything forward of the power from CR1A on the board, tune it to roughly 33 volts and continue to use the built in voltage regulator to send 27VDC to the rest of the board. The EPS-35-36 can be had for around $15 online from what I've been able to find. They are 3" x 2" x 1". Not exactly small, but not huge either. Other than moving the bulk for the walwart to inside the amp case, can anyone see a reason this wouldn't work?
The only way you won't degrade performance with the MOSFET-MAX's onboard linear-regulated power supply is to use one of AMB's Sigma 11 power supplies. The performance on the MAX/MiniMAX is about 45uV noise. AMB's is down in the single digits of uV supposedly, but I kind of doubt that you would notice the difference with a tube/tube-hybrid amp (the tubes usually have more noise than that). In any event, there is no commercial switching power supply that's going to meet those kind of specs.
The Meanwell power supply you've sugested has 200mV ripple (noise). That's absolutely atrocious for audio, IMHO. It represents over 4000 times more noise than the MAX V1.2 PCB's onboard power supply (200 vs. 0.045). It may even be audible (ripple hum) in certain situations, but the performance will be degraded well before that - fat, loose bass, and other artifacts.
Edited by tomb - 9/11/12 at 4:56pm