Dual PPIMV LM Layout by SDM

[white noise]

Has anyone used the layout by SDM for the Dual PPIMV LM?

Here is a link to it:

https://drive.google.com/folderview?id= ... jdaSFNBOGM

[Tone_Chaser]

I use it on my build. The relay is connected to a foot switch so I can switch between lead and rhythm volumes while playing live. It works great.

[white noise]

thanks for the reply, what type of "Glue" did you use to "Glue" the relay to the back of the Pot?
Or did you not attach it to the pot?

[SDM]

Think when I originally drew that up, it needed to take up absolute minimal space. Hence gluing the relay to a pot. Not necessary to do that of course, but the relay has very little weight, hot glue is easy to use, easy to remove if you do want to mount it on a pot.

Over the years many have reported using this dual PPIMV setup successfully. Some use pre-made relay control boards to power the relay, some use the simple Jubilee circuit, some use another solution. Shouldn't have an issue with any of them.

[white noise]

thanks for the info Steve, hope everything is going good for you.

[white noise]

Steve,

Have you ever tried to use 2 Dual 250KA pots for the Dual PPIMV.

The Larmar uses 250KA Dual pot for the Single PPIMV.
Georges uses 500K Dual pot for the Single PPIMV.

Bray uses 250KA Dual pots for his Dual PPIMV.

Is there a certain reason your layout says to use "Dual 500KA" pots?

[SDM]

Is there a certain reason your layout says to use "Dual 500KA" pots?

Yes. The way the pots are wired, the resistance value of the two pots halves stay in parallel. So two 500K pots equals a 250K total PI load per side. Without a PPIMV, the most common PI loading is 220K, and 250K is close enough. Ultimately, just means the PI gain and frequency response stays pretty much the same as if no PPIMV was there in this part of the circuit.

Other parts of the circuit (namely NFB) are still in play of course, change as a PPIMV is lowered/turned down, but my thinking was to essentially make the PPIMV "disappear" when cranked up. So people could still get the original tone out of the amp whenever they wanted to.

This assumes an amp with 220K grid leaks (or "bias splitters" as some refer to them) to start with. If it had other values or you wanted some change in frequency response or such, no harm in other values for the pots to help match other values or to achieve a desired change/effect.

[white noise]

Steve,

thank you for the comment!
I wasn't thinking they were in parallel but makes perfect sense now.

So the amp should have the 220K grid leaks installed (stock 2203) unlike the Larmar PPIMV that has the 220K grid leaks removed?

[SDM]

The grid leaks should be removed. Was just referencing them to compare things to an amp in stock form (i.e. no PPIMV/s).

The dual PPIMV setup (with dual 500K pots used) "mimics" and replaces the original 220k grid leak resistors at darn near the original values was the point I was trying to get to. Hope that's clearer.

[white noise]

Than you Steve!

As always excellent explanation.

[ledvedder]

Sorry to bump an old thread.

Has anyone else done this? Could I get more information about it? I'm surprised there isn't more out on the interwebs about this.

[danman]

I added this to a JJ Jr style build that I did a few years ago. It works great if you have the channel switching in place to utilize it. The board that I used for the build was from Head First Amplification. He includes the dual master option into his boards.
https://headfirstamplification.com/pcbs-for-diy