Pre LTP PI MV?

[Daedalus]

Has anyone ever put a MV pot just in front of a LTP PI?

[Daver]

Yep. That's pretty much a classic way to do it. Check out the Marshall schematic link.
Dave

http://www.freeinfosociety.com/elect...iew.php?id=486

[daz]

thats where mine is. Some say post PI is better, but my amp sounds better pre. Marshall did it that way so they must have a reason. after all, it wouldn't cost anymore to build them with a crossline master.

[Steve A.]

Has anyone ever put a MV pot just in front of a LTP PI?

The rule of thumb is if you have plenty of gain in the preamp, a pre-PI MV will work just fine. For example, the Marshall 2203/4 added a gain stage before the DC-coupled pair, so the design works fine with the pre-PI MV. However, with the classic Fender and Marshall designs from the 60's you lose the distortion in the PI when using as pre-PI MV so most people prefer the post-PI MV's in those amps (if you are going to add one at all).

Ken Fischer spells out 4 different MV designs in his trainwreck pages- fascinating reading!

http://www.blueguitar.org/new/schem/...reck_pages.pdf

Steve Ahola

[ETR]

The rule of thumb is if you have plenty of gain in the preamp, a pre-PI MV will work just fine. For example, the Marshall 2203/4 added a gain stage before the DC-coupled pair, so the design works fine with the pre-PI MV. However, with the classic Fender and Marshall designs from the 60's you lose the distortion in the PI when using as pre-PI MV so most people prefer the post-PI MV's in those amps (if you are going to add one at all).

Ken Fischer spells out 4 different MV designs in his trainwreck pages- fascinating reading!

http://www.blueguitar.org/new/schem/...reck_pages.pdf

Steve Ahola

Does anyone get what he says about adding half the filament voltage to the bias?

[Jag]

He says that in relation to adding a MV? Which page?

[anson]

MV's before the PI are good for allowing your negative feedback loop to do its job at all MV settings. Post PI master volume controls make the global negative feedback loop ineffective at low volume settings, so your presence/resonance knobs wont be as effective. Post PI master volumes can still sound awesome though......