Originally posted by Helmholtz
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This is "gain structure". If the amp you have gets much of it's distorted tone from clipping the power tubes, and the master volume is before the power tubes the power tubes will not be distorted when drive to them has been reduced (simple). That said, preamps can generate distortions of their own. Though typicially at higher drive levels than where the power tubes do (NOTE: Otherwise it would be impossible to get a full volume clean tone from the amp!). So when a master volume is included you should actually expect LESS distortion than what you get with no master volume, but playing at higher volume with the power tubes driven into distortion.
There is one exception... Modern high gain amps are typically designed to get distortion from the preamp and then the power amp is (by design) limited to amplifying ONLY what the preamp is doing in it's distortion generating. This is a good case for why such amps are often channel switching. Because it takes a different preamp topology to achieve max clean tone than it does to achieve max "preamp distortion" tone. So different "channels" are needed for intuitive performance.
I don't fault any guitar player, and that includes you SeaChief, for seeing the state of modern amps and distortions hard to grasp. This divide in understanding has been the bane of designers since square wave clipped signals became popular in the 60's!!! So no one is accusing anyone of "failing" to understand the circumstances. Learning gain structures as they apply to guitar amps can be hard for the lay players. I only ever pointed it out here because it would benefit you a lot on the path you're taking. Especially considering that you know tone and own a Twin Reverb and an AC30 for your own reasons. You know what these amps sound like. So how to make them sound like that without skinning the neighbors? I like attenuators because I feel these tones are best represented when the amps are at least humping the way they did on the recordings, right.?. But the simpler "master volume" solution is SOOOO attractive and circuits abound from people that claim to have managed what it will take to "unlock your amps tone" BULLSHIT. (<period) Master volumes suck the life out of vintage design amps like the TR and AC30. But that isn't to say that they don't have merit BECAUSE...
Players who understand the gain process through an amplifier can make concessions or corrections for what's NOT happening and find themselves on the happy side of what they get for a tone. These players are in the minority. Much to the shagrin of designers. That said...
A guy who has a GREAT understanding of gain structure without being an official electronics nerd would be Pete Thorn. His *outube videos are a great source for players to glean some understanding of what gear implementation and manner of use mean to "tone".
Not sure if this helps. I'm trying a different idea.
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