PPIMV on Twreck

[erigm]

Omar, how well does the PPIMV work on an Express style of amp? Thanks!

[Omar]

I've been very happy with the PPIMV. I used a 250k dual pot for my T-Wreck - no extra caps - per one of Ken Fischer's example in the Wreck Pages. I like running it around 12 o'clock and using the preamp volume to dial in the gain level. It's sounds very full at 12 o'clock and I find that beyond 2 o'clock it doesn't change the volume but changes how the amp compresses, which is neat.

I know that the PPIMV is not a Trainwreck thing (neither were the switchable rectifier or switchable B+ I used in my amp) but I think it's nice to have that added control to the overall volume plus the compression thing.

Omar

[RossH]

I used a pre-PI MV on mine (500k pot to ground). I like that too. You can always make it switchable if you'd like. It does give added flexibility and doesn't seem to get in the way.

Ross

[MikeKCA]

Ross:
I've been thinking about a 1Meg Pre-PI MV with a pull switch in engage/disengage the pot.

Do you get the same amount of grind when you back off on the PI? I'm wondering how much extra distortion the PI produces under normal operating conditions.

[RossH]

Do you get the same amount of grind when you back off on the PI? I'm wondering how much extra distortion the PI produces under normal operating conditions.

When building my wreck I asked Paul Ruby that question. Here is that exchange:
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What are your thoughts on a Pre-PI MV versus a post-PI crossline style?

The answer depends on the amp and how much of it's tone is from the PI. For a wreck, most all the distortion comes from the 3rd stage. So, a MV right after that will work well. If you choose to back off the gain of the 3rd stage sot the PI can be pushed AND you use power tubes that need a lot of drive from the PI (like KT66), then the post PI MV might make sense because the PI is playing a role in the distortion.
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I've never tried the crossline on my 'wreck. I like mine the way it is. I suppose you may get a little more with the crossline style. I don't even crank my gain all the way up with the pre-PI type.

HTH,
Ross

[loverocker]

Interesting - I'm going to temporarily wire in a simple post-PI MV on my Liverpool to see how useful it is.