Re: For non master volume amps... how does it work?
I'm going to attempt an explanation of this to see how much of an understanding of it I do. If I'm wrong, i'll delete the post when someone chimes in so dont take my word for it yet!
Ok. With a post-phase inveter master volume amp, the gain is the preamp volume. Basically controlling the output volume of the first gain stage (like on a Vox AC30). The master volume acts as a volume control after the phase inverter has already done it's job. The difference between the two is that the gain or preamp volume is actually controlling how much to amplify the signal, while a PPIMV controls how much of the already amplified signal to shunt to ground, and the rest gets sent to the power tubes.
A non-master volume amp basically doesn't have the volume controlling the already amplified signal. The only volume control on the amp would be the one coming out of the first gain stage. In that respect, the power tubes are always cranking out what you dial in, whereas with a PPIMV you can crank that preamp and chill the poweramp out for breakup. Generally speaking, non-master volume amps are characterized by power tube distortion, since by the time you get the preamp to distort enough, you better be wearing ear protection!
The problem I have with non-master volume amps is that when you want to play below 3 on the volume knob, the tone sucks since the signal is barely being amplified. On the sound city I used to own, anything below three on the volume and you were wasting your time. HOWEVER, turn it up past three and get the tubes cooking and it was heaven in a tolexed box. that's why the Vox AC30 I'm builind now is getting a PPIMV control.
To answer your other questions: I dont know if the preamp is designed to stay clean. Maybe on some amps, but on others like the Marshall JTMs I cant imagine so. I found the distortion on my sound city to start with a little poweramp "spanky" kind of sound, then as you turned it up the preamp and poweramp would start to crunch almost simultaneously. I found full poweramp distortion to be around 7.5 with my sound city, from there the rest on the volume knob seemed to add only a little bit of preamp gain (I may be wrong about that though). At 7/7.5 on the amp volume, I was able to roll back my guitar volume for decent cleans, after that forget it it was crunchy no matter what.
Hope I actually made sense.
Thanks dude!
