Larmar PPIMV hum and lead dress

[GtrScott]

Hi,
I just installed a Larmar PPIMV in an older Germino Lead 55 and have a couple issues. There is a hum when the MV is all the way up. If I touch the chassis near the pot, the hum is reduced. The pot dual pot is right over the v3 PI socket (see pic). The potentially dumb question is, could this cause the hum?

Also, the bass seems very compressed and tubby. Is that expected tone or do I have other issues?
Thanks

[Deric]

Is the shield from the shielded wires connected to the blue wire/left lugs on the pot? Probably is but can't tell for sure by the pic.

Does it still hum when loaded in the head cab?

Does look close to V3 but in my experience that's never been to big of an issue. Might try moving the LarMar wires around - raise them up as high and clear of other components as you can.

Interesting that the PI plate resistors are on the opposite side of the board from what I've usually seen. In my experience the PI plate wires can be somewhat picky about lead dress....

Here's a pic of a LarMar I recently installed in a Lead55 for reference. Had zero noise/hum issues. Sounded great.

[GtrScott]

Is the shield from the shielded wires connected to the blue wire/left lugs on the pot? Probably is but can't tell for sure by the pic.

Yes it is.

Does it still hum when loaded in the head cab?

I'll try it tonight

Might try moving the LarMar wires around - raise them up as high and clear of other components as you can.

I did that and nothing changed.

Here's a pic of a LarMar I recently installed in a Lead55 for reference. Had zero noise/hum issues. Sounded great.

Thanks for the pic! The only real difference I can see is that I have more unshielded wire to v5.

[Deric]

Just noticed....

As it's wired now you have no negative feedback. The purple wire needs to go to the other side of the speaker jack. If the lugs were connected like the one I worked on it would make no difference.....

Better pic attached...

[GtrScott]

Just noticed....

As it's wired now you have no negative feedback. The purple wire needs to go to the other side of the speaker jack. If the lugs were connected like the one I worked on it would make no difference.....

Better pic attached...

I wondered about that. Looking at the jack, the two sides appeared to be the same piece of metal wrapped around the plastic so I assumed it would be ok without the jumper across. But I'll change that too.

That would probably account for the funky tone.

Thanks!!

[GtrScott]

I hooked up the NF wire properly and the hum is gone.

The fuzz type tone is still there. When turn up the MV all the way and crank the amp to 5, it sounds great. When I turn the amp to 5 and bring up the MV it sounds like, well, poop.

[Littlewyan]

Do you mean when you have the MV low down it sounds fuzzy? As I believe this can be normal as with the MV low down you haven't really got any NFB. I don't think its meant to be massively bad though.

[Stevem]

Yes, and you mainly have preamp distortion which sounds like shit without enough stages of it taking place to not have any one stage being over drivin by more than 12 db!
More than this and the Harmonics that get produced by the level of clipping are what the ear here's as being nasty, not so much the fuzz!

Do a search for the 1973 paper called " tubes verses transistors, Is there a audible difference " and read it thru a few times and you will see how there findings relate to having good distortion and how Pentodes and Triodes produce different Harmonics when pushed into clipping.

[GtrScott]

Thanks I'll check for the article. It does seem to get better as it gets louder and that goes along with what you and many others have said.

I'm going to try it at a gig tonight and see how it sounds.

Thank everyone for your knowledge and help. It's much appreciated!!