PPIMV LOUD HUM

[rockstah]

Strange.....


100w 1959 circuit.

Lar/mar ppimv which I have installed many times.

With the bright and normal volumes on zero and the PPIMV on zero I get a loud hum. With the PPIMV ON 10 the hum goes away.

Any ideas?

Mark

[Gaz]

I thought you invented it

[Cliff Schecht]

Strange.....


100w 1959 circuit.

Lar/mar ppimv which I have installed many times.

With the bright and normal volumes on zero and the PPIMV on zero I get a loud hum. With the PPIMV ON 10 the hum goes away.

Any ideas?

Mark

Sounds like the pot body is not shielding the internals at all. I had this problem recently on my Vibroverb build with the reverb pot, it would hum when turned down but would be hum free when maxed. The fix for me was adding one of those little washers with a long solder tab that went around the pot shaft (in between the pot and the amp on the inside) and soldered directly to the ground lug of the pot. Cleaned the hum right on up.

How is the PPIMV pot grounded? Is the body of the pot grounded at a different location than the lugs of the pot?

[roberto]

I quote Cliff, but an internal picture would be useful.
Check pot grounding to chassis.

[rockstah]

again, i have installed these many times with no issues. maybe its time to try another choke.

it just doesn't make sense as to why its loud on zero and gone on 10.

the added washer seems it would fix masters that are grounded to the chassis.

[IMG:785:689]http://i24.photobucket.com/albums/c44/m ... Logpot.gif[/img]

[Reeltarded]

I thought you invented it

Nice!

[roberto]

It has sense, if you have ripple on bias voltage, so a bias cap that's dry.

[Jana]

I would suspect a bad pot that isn't making good contact with the trace and it's "ground" tab.

[rockstah]

It has sense, if you have ripple on bias voltage, so a bias cap that's dry.

i guess i will swap in new caps but they are new...hmmm

[rockstah]

I thought you invented it

Nice!

This master was developed over at Metroamp.

When i was trying it inside a marshall, while looking for a better solution, (i didn't like the way the rich mod sounded) I came across it pouring through ken fisher data.

It was Larry that came along and added the safety resistors.

The name, Lar/Mar PPIMV was to have reference point to this improved master. Nothing more nothing less.

Now you know the rest of the story.

Mark

[rockstah]

I would suspect a bad pot that isn't making good contact with the trace and it's "ground" tab.

i swapped out the pot and checked all connections.

[Jana]

Just out of curiosity, measure the bias voltage going to the power tubes at various settings of the pot. Measure at the grids of the power tubes to get the actual reading and not at the bias feed portion of the circuit.

[rockstah]

Just out of curiosity, measure the bias voltage going to the power tubes at various settings of the pot. Measure at the grids of the power tubes to get the actual reading and not at the bias feed portion of the circuit.

did that. -41.89 dcv at all settings of the pot on all tube grids.

[Firestorm]

Does the hum diminish gradually from 0 to 10? Or is there a sudden drop when the wiper hits any resistance?

[rockstah]

Does the hum diminish gradually from 0 to 10? Or is there a sudden drop when the wiper hits any resistance?

gradually as the volumes goes up to 10 where it goes away completely.