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bubbab74 19th November 2009 01:59 AM

Tube Amp Channel Switching
 
I'm implementing a channel switch for a small tube amp I'm building and need some help. Here's what I want to do:
  1. Switch between 2 seperate gain controls, each one being a dual pot.
  2. Have a toggle switch on the front panel.
  3. Have a footswitch pedal that disengages the front panel switch when plugged in.
  4. An LED that lights for each channel, regardless of which switching method is used.

Any ideas or schematics out there I can reference? Thanks, guys. :)

m6tt 19th November 2009 05:29 PM

I make guitar amps, but I've never really been into the mesa boogie channel switching relay thing. Instead, I'll make separate preamps if I need them, and then use those pots with the integrated switch on the back. I'll LED bias the last stage in each pre, but like this:

Cathode ---> (+) LED (-) ----> Switch ----> Ground.

Resistors would work too, but you can panel mount the LED to indicate the channel is on.
If you turn the volume to "off" for a channel, the cathode gets lifted, and thus no sound. If there are two channels in parallel, you can get one or both. To use a footswitch, use a closed-circuit (shorting) 1/4 jack and have it swap the pot switch for the footswitch when the 1/4 is installed.

I generally use a floating or appropriately referenced filament supply, since the cathode will go up to B+ potential when lifted.

I hope this helps, it's the easiest way to implement multiple channels i've come up with lately (just used it in a big 100W with high gain & low gain guitar + high gain mic pre).


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