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On my plexi, what cause the following to happen ???

When I'm plugged into channel 1 and I increase the volume of the drive channel (with nothing plugged into it), the treble gets cut back and the volume decreased slightly on channel 1.

Is this something that can be overcome ??

thanks...

How is the channel switching implemented?

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Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

Hi Richard,

Thanks for responding.

For channel switching I use an A/B/Y box on the input, but this happens even when I'm not using my A/B/Y switch. For example when I plug the guitar directly into channel 1 and turn the volume up on the T/M/B drive channel the treble is cut down on channel 1.

At one point I removed the 500pf cap on the volume control to reduce that channel's bite, but now I'm thinking of putting it back in (switchable) to compensate.

Is there was something else I should be doing ??

cheers,

Brian

What's happening is that C7 provides more drive when it is connected to ground and you are negating that when turning up the volume control.

Here's an idea. You can sum the channels into the 'normal' side of the PI. Use a couple of 220k resistors to do this. Here's how. Connect one end of each 220k to the wipers of VR7 and VR3 then connect them together. Then connect the connected side to C6. Connect C7 to ground. You can even try a .022-.1 for C7 when grounding it for more drive. This setup is more like the summing used on the larger Plexi style amps. VR7 and VR3 will still interact a little. You can increase the 220k resistors to 470k to lessen the effects of this.

No solution is going to be perfect.

_________________
Richard Johnson
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Playing an insturment doesn't make you a musician, listening does

thanks Richard, I'll give that a try