Problem witth Larry Grounding Scheme -

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Problem witth Larry Grounding Scheme -

Post by QOTSA_Lover » Mon Jun 08, 2020 5:50 am

Hey Guys,

maybe someone can chime in and help me locating my problem.
I built a 1969 Plexi 50 Clone. Amp works so far and sounds pretty nice.
On my first build I used the typical Marshall Grounding - and the amp is dead quiet.

On my 2nd build I wanted to do it better and wired the grounds with Larrys Grounding Scheme.
I drilled 5 holes in a line and wired the grounds as following:

1st node: Heater CT, V1 Cathode, Input Jacks
2nd node: V2 Cathodes, Volume Pots, Preamp Filter
3rd node: Mid & Pres Pot, Screen & PI Filter (shared 50&50uf), Speaker Jacks
4th node: BIAS only
5th node: HT CT, Kathodes EL34, Mains Filter

A PPIMV LarMar is installed. Amps works. Everything seems to work properbly. But there is a noticable hum the more I turn up the volumes.

Plugged only into the high treble seems to be the most quiet operation. The more I turn up the volume, the more hum chimes in.

Even when nothing plugged in, the normal channel volume pruduces a loud hum past noon.
When I jumper the channels (jumper from High Treble Lo to Normal Hi) and touch the jumper cables plugs I get a strange buzz.

The High Treble Lo pruduces more hum than the High Treble Hi.

When I pull the V1 Tube the hum gets louder.
V1 back in and V2 pulled the amp is dead but the hum goes away.

Maybe someone can help me with my hum problem?
Thank you so much for your time and help.

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