ez wrote
I think what Mike is referring to is the fact that with a PPIMV dialed lower, you get less overdrive from the power tubes. A PPIMV sits between the phase inverter (12ax7 in your plexi I think) and the power tubes. So, without the PPIMV and diming the volume knob, you get some PI overdrive and some power tube overdrive and the the more you turn the volume up the more of both you get. However, as you experienced, the amp is loud at this setting, so hence you installed the volume control. Now, when you dial the PPIMV down, you still get the PI drive but the signal is begin reduced after that. That means the power tubes are getting a smaller signal which will not push them hard and hence you lose out on the overdrive effect they would have given you. You win by getting some overdrive at lower volume but you lose because you sit with less overdrive than you would have had. I'm not surprised he can hear a difference. It should be obvious.
Thanks, I get what you guys are saying, and you're right, it should be obvious, and with multi-channel master volume amps I've owned in the past, I've detected a clear difference in tone between cranking the master volume to full, and controlling overall volume with the gain knob (power tube distortion), versus cranking the preamp volume/gain and controlling overall volume with the master volume control (preamp distortion). Am I on the right track so far?
I guess what I was getting at initially is that with the Plexi and the PPIMV, the difference in tone, except at the lowest PPIMV levels, is not as obvious as I would have expected. In a good way. Nothing like the differences noted above with other amps I've owned, where I had a strong preference for the tone with MV cranked, and a lower volume/gain setting on the preamp.
