Why Few PPIMV in Production amps?

[fusionbear]

Another noobish question for you. My electronics background is in CT and MRI, so the guitar amp world is pretty new to me. I've noticed that most amps I've worked on have the Master before the PI and many have it in the tone stack and then the post MV signal goes to another gain stage and finally to the PI and power tubes. Why is this? It seems a lot of the mods I've been doing lately to Marshall and Marshall clones is add a PPIMV. Is there something inherently wrong with this type of MV? Are there any precautions or special components needed to do the PPIMV in a cathode biased output tube amp?

[SatelliteAmps]

My experience has been that they are all just different ways to accomplish the same thing. They all have their inherent positives and negatives, and they all work a little bit different in how the tone is affected. PPIMV's are about as easy as they come, but the curve on them doesn't appeal to everyone (how much control you actually get).

And no, there aren't any special precautions or components needed that wouldn't apply to any of the other styles of master volumes.

[John Phillips]

Another noobish question for you. My electronics background is in CT and MRI, so the guitar amp world is pretty new to me. I've noticed that most amps I've worked on have the Master before the PI and many have it in the tone stack and then the post MV signal goes to another gain stage and finally to the PI and power tubes. Why is this? It seems a lot of the mods I've been doing lately to Marshall and Marshall clones is add a PPIMV. Is there something inherently wrong with this type of MV? Are there any precautions or special components needed to do the PPIMV in a cathode biased output tube amp?No, in fact it's slightly easier, because the grids are referenced to ground and not the bias voltage, so you can use a straightforward dual pot without needing to use extra caps to avoid DC on the pot.

Some production amps do use PPIMVs - two examples at the opposite ends of the price/quality scale are Matchless and the Marshall DSL401 - but I have no idea why they're not more common either. The only real disadvantages I can think of are that if you're to do it with a 'proper' (rather than cross-line) scheme, the dual pot needed is slightly more expensive than a single; and that in an amp with heavy negative feedback the MV disrupts this as it's turned down and can sound a bit odd.

[ruger9]

My RXJR has a PPIMV MV. And it's great. But so is the PRE-PI MV on my Black Pearl. As most things with amps, the EXECUTION is all-important.

[epluribus]

Check here:

http://www.people.cornell.edu/pages/mt24/Amp/mm/mvols.html

A nice summary of several approaches to MV. The author speaks more from practical experience than a deep theoretical standpoint, and he very nicely makes clear he's sharing personal experience, not an authoritative be-all and end-all. Same caveat applies throughout the site, but there's a lot of other good stuff there as well.

--Ray