Bazzman

[rdjones]

Here is the updated schematic in case anyone is interested.
/Bazzman-rev4_webb.jpg

Does the Z channel volume control have any effect on the sound when playing through the F channel ?
I suspect the inherent imbalance in the PI is being increased due to being driven from alternate sides.

Normally in a long tail the second phase is driven from it's cathode and has it's grid referenced to ground through a cap and then the tail resistor.
Your circuit is using the Z channels coupling cap to ground reference the upper PI triode when using the F channel, but only when the Z volume is at 0.
When using the Z channel that grid reference has to go through the 100k plate load of the second triode of the F channel.

I know I've not explained what I see very well and there may be a technical reason why it would still work.
I still can't help thinking this is further unbalancing the PI, though.

Also, any bias balance adjustment being made from center would be defeated when the cross-line master is at or near 0.

reddog

[Lynxtrap]

Does the Z channel volume control have any effect on the sound when playing through the F channel ?
I suspect the inherent imbalance in the PI is being increased due to being driven from alternate sides.

Normally in a long tail the second phase is driven from it's cathode and has it's grid referenced to ground through a cap and then the tail resistor.
Your circuit is using the Z channels coupling cap to ground reference the upper PI triode when using the F channel, but only when the Z volume is at 0.
When using the Z channel that grid reference has to go through the 100k plate load of the second triode of the F channel.

Thanks for the response! I'm not sure I understand everything about this.
I actually borrowed this solution from the Vox AC50. I thought the ground reference was the 22K at the junction between grids and cathodes.

The Z-channel's volume does not seem to have an effect on the F-channel. I've tried this to check for interference.

Also, any bias balance adjustment being made from center would be defeated when the cross-line master is at or near 0.

That has crossed my mind, and now I'm getting worried
Does that mean both cut and master are throwing off bias balance all the time? Does the DC-30 do this also? Or is it nothing to worry about, except the balance pot is useles?

[Lynxtrap]

Anyone else with thoughts on the PI and bias issues..?

[Lynxtrap]

I tried to make a few soundclips tonight. One track for each channel. It's all played on a Fender '52RI Tele.

http://soundcloud.com/tom-forsman/sets/bazzman-test

[Lynxtrap]

After testing the amp at rehearsals, I'm starting to think that low headroom is a problem. Can't see any other reasons than the changes to the PI (compared to the stock Fender circuit).
It's breaking up at 3 on the channel volumes with master at 10.

Any suggestions to increase headroom a bit?