PPIMV and ghost notes or oscillation

[xtian]

I put PPIMVs in both my Fiddy (Marshall 1987) builds. First amp is fine. Second amp exhibits ghosting, or oscillation when playing only E, two octaves above low E.

I'm thinking it's the PPIMV, because if I turn up the PPIMV to 100%, the ghosting vanishes.

I read recently a suggestion to separate, instead of twist, wires going from the PPIMV pot to the power tubes…at least I think that was it. I can't find that post.

Anyone have this experience?

[Reeltarded]

Yep! Shield all the way. I have about 2 inches popped out of the shield, just enough to make the distance to the resistors. Shielded wire to pot, and to the tubes.

I don't recall what the wire type is. two conductors and shield, black, a little stiff but the wire isn't wrapped very tight in there.

[Structo]

Yeah, that old lead dressing can make all the difference.

[Reeltarded]

I hate to break up a topic so early, but I have a real problem with collaapsing the NFB because presence is so important to the impact and sing of the played note. Sure, that all probably gets rolled off down the line, but damn..

My free lunch is the Jose cathode master and the simple master playing well together. Have you tried that before? The Jose is a...

Move the 100k resistor off the board to pin 8 of V2.

Add 10k at same pin.

Add a .22 or .33 off the end of that 10k.

The end of that .22 finds the (looking at the back, lugs up) right lug of a 1M audio pot arranged just as the simple master, left lug to ground.

The center goes to the junction of the treble cap and slope resistor.

All done.

RAGING awesomeness.

For extra points, string an opposing diode pair across the outside lugs for a clipping network, or from the input lug to another 5kL pot arranged as a ground bleeder to control the amount of grind vs volume. (left lug input, center lug is ground)

You get 1000 useful tones at the turn of 4 knobs. Like having a pile of amps in one box. I was going to share the diode control earlier. On the ipad I have no graphics drawing capability.

[Richie]

I put PPIMVs in both my Fiddy (Marshall 1987) builds. First amp is fine. Second amp exhibits ghosting, or oscillation when playing only E, two octaves above low E.

I'm thinking it's the PPIMV, because if I turn up the PPIMV to 100%, the ghosting vanishes.

I read recently a suggestion to separate, instead of twist, wires going from the PPIMV pot to the power tubes…at least I think that was it. I can't find that post.

Anyone have this experience?

That was probably me a few days ago, since i think i am the only one that has posted that info. You can use shielded wire, but use seperate or single conductor for each to the tube. Don't have both wires inside the shield thats going to each side or half of the tubes.
Or first just try un-twisting them, and seperating them apart in the run from the pot to the tube connections.

As for ghosting, that could be from a not so good ground connection. If its a marshall type amp, or chassis that has the anodized look to it. be sure to get a good contact to ground.

[M Fowler]

Richie, I did what you said on my last Express using separate shielded wires for the Lar-Mar MV and good lordie what a freaking pain in the arse wiring up all those components, wire and shields. But it surely works very well thanks buddy.

I think next time I'm going to make a small board to connect all the wires and components to using dual PCB terminal pot.

Mark

[vibratoking]

I have been frustrated by ghost notes on various amps. Nothing related to adding MV so it may be completely different than your issue. Mine have mainly been cured by resoldering every solder joint in the amp. I did not take the time to determine the exact joint that caused the problem, I just resoldered them all. Problem solved. This situation has occurred many times. There have been a few times that lead dress fixed the problem as well.

[xtian]

I think next time I'm going to make a small board to connect all the wires and components to using dual PCB terminal pot.

This has potential (pun intended) to add to the LarMar legacy, Mark. Hope you carry through.