This amp is quieter than either the ST-70 or the ST-120 and those two amps (if built correctly) are pretty quiet. I had a friend with some test equipment who lives near Boston run both prototype amps through some tests. He came up with about a 95 dB signal to noise ratio. Some reason's why ..
1. Stainless steel chassis
2. Only one channel on the amp
3. The use of an ST-70 type power supply and grounding system rather than a Mark III
4. Lower gain level of the M-125 amp vs the ST-70/ST-120 amps
I recommend to each amp builder that he use screened low noise 12BH7A driver tubes especially for the front voltage amplifier tube. For the rear 12BH7A phase splitter/phase inverter tube the use of a low noise tube is not as important.
NOTE - The photo below is of an earlier VTA M-125. The newer CCS M-125's as of Jan 2014 have a very slightly different wiring of the driver board. The rest of the wiring is the same as the wiring shown in the photo below ..
Last edited by Bob Latino on Mon Aug 01, 2016 4:59 pm; edited 4 times in total