Amp Master Volume question

[dfwadjuster]

I have read that some Master volumes, when turned to 10 (or whatever number is Max) will then cause the amp to act as a Non Master amp.
1. Is that the case?
2. If it is, is that not the case with all MV amps?
3. If so, then how would one know if their particular MV amp would indeed act in this way. A Jet City for instance?

Thanks in advance.

[Bruce / Mission Amps]

If the actual pot used for the MV has enough resistance... like at least 1Meg... the chances are pretty good you would not hear much difference between it up all the way and the same amp with a straight piece of wire.... BUT.. that is not the idea of a MV amp.
Many MV amps have an extra preceding gain stage that allows you to turn the MV pot down and that amp's preamp volume up, causing preamp distortion directly ahead of the MV.... so the next stage, like a phase inverter, dutifully replicates the distorted preamp and on to the power tubes which also do the same while creating no additional distortion.

[Chuck H]

+1

Just to say it another way... WRT master volume "mods" for vintage and vintage styled amps it is generally considered best if the particular master volume circuit allows the amp to operate as stock with the control turned up full. And to answer your question #2, not all master volume circuits are considered good for this. For any amp that was built with a master volume it shouldn't matter because the amp was designed to work with the master volume as part of it's proper operation.

I expect the amp in question was designed with a master volume. If yes, then with the master all the way up the amp is operating at it's loudest/cleanest setting. To have it operate as a non master volume amp isn't even a consideration. Because there is no otherwise identical non master model for it to sound more like.

[Steve Conner]

With most MV amps, I'd expect to be able to turn the master up full, use the gain knob as the volume control, and get similar tones to a non-MV amp.

Downsides: There could well be an annoying level of hiss on account of the extra gain stage, as explained above. And MV amps tend to have a high output power, so if you want to get a traditional non-MV tone by overdriving the power tubes, it can be painfully, apartment-evictingly loud.

On channel-switching amps, the clean or rhythm channel is probably closest in topology to a non-MV amp, so I'd expect the master-up-full strategy to work best on this channel.