crosstalk, coupling, bleeding whatever it's called....

[AmpegSVT]

I have built myself a rocket/zwreck amp. I recently installed a 1M master volume from the treble wiper to ground, then the MV wiper to the 220k/220k voltage divider b4 the phase inverter input cap. When the MV is turned to zero I get quite a bit of signal leaking into the phase inverter. The problem goes away if I bypass the 220k/220k resistors and go directly to the PI input cap. While looking for the souce of this leak I tried disconnecting the input to the PI input cap and just left it unconnected. Man that PI input cap is super sensitive! Its almost if there was a wire connected directly to the preamp stage. I also disconnected the input directly at the PI tube. It still picks up some leakage but VERY little. It it normal for the PI to pick up radiated noise like that?

[tubeswell]

Can you post a schematic of what you built?

[AmpegSVT]

Here is the area in question, you can see where the MV is added.

[Darkbluemurder]

The tone caps may be too close to the PI input cap. Can you post a picture of your build, please?

Cheers Stephan

[Tillydog]

Also: Where (exactly) did you connect the ground for the MV pot?

[M Fowler]

How about not using a voltage divider with the MV.

Instead connect one of your 220k (R11) between treble wiper and MV pot entrance and then the other 220k (R10) from MV wiper to PI.

[AmpegSVT]

Heres a photo of it. I already removed the master volume. The MV was where the cut control (last pot on right) was. I had removed the cut control altogether. I grounded the MV control to the back of the pot. The main reason for the master volume install was to to reduce hiss from the effects loop that I also had installed. When I was experimenting with the master volume and noticed the heavy crosstalk, the effects loop was not connected.

[M Fowler]

An effects loop isn't needed with this amp all effects can go straight in front of the amp without any loading problems even reverb.

But if you do want the cut control which I use a lot, plus MV, and effects loop all of that can be done without much trouble.

Use shielded wire on that effects loop though.

[Structo]

Double check the pot in question.

I've had defective pots that did that before.

Make sure it actually goes to 0 as well as the sweep up to the total value.

[rdjones]

Signal is traveling through your chassis.
It can be power amp tube grounds from the cathodes, OT secondary to the speaker ground, PI ground or NFB ground (if present).

These all need to be grounded to a common point (i.e. "power amp ground point") and not have the signal/power grounds use the chassis as a return path.

The master volume should ground to the same point as the PI/power amp (and OT secondary if NFB is used) ground.

Hope this makes sense.

RedDog Steve