Simple technique for guitar amp channel switching?

leadbelly · 30th August 2008, 08:38 PM

I've been searching through guitar amp schematics to see if there is a simple technique for channel switching by footswitch.

For opamp based amps, there is a simple method of ungrounding the feedback network of a stage to silence that same opamp stage. This lends to a very easy to implement footswitch requiring only one contact and no relays or other devices.

I was looking through commercial tube guitar amp schematics but could find no equivalent trick, all I could find were relay based channel switching by footswitches. Any ideas?

leadbelly · 2nd September 2008, 03:26 AM

Anybody? Bueller...Bueller...

How about ungrounding the cathode bias network? Is this OK if the grid and anode remain terminated?

PRNDL · 2nd September 2008, 01:32 PM

There are several issues to contend with: tube impedance, how much signal is bled through, and sending audio through the cable to the switch.

Relays solve a lot of problems and allow channel switching without "tricks", which is why they are used.

The Super Twin Reverb did use a foot switch to change the bias point of a preamp tube to move it into distortion. Unfortunately, most people did not like the tone.

30th August 2008, 08:38 PM	#1
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Simple technique for guitar amp channel switching? I've been searching through guitar amp schematics to see if there is a simple technique for channel switching by footswitch. For opamp based amps, there is a simple method of ungrounding the feedback network of a stage to silence that same opamp stage. This lends to a very easy to implement footswitch requiring only one contact and no relays or other devices. I was looking through commercial tube guitar amp schematics but could find no equivalent trick, all I could find were relay based channel switching by footswitches. Any ideas? __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

2nd September 2008, 03:26 AM	#2
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Anybody? Bueller...Bueller... How about ungrounding the cathode bias network? Is this OK if the grid and anode remain terminated? __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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2nd September 2008, 01:32 PM	#3
PRNDL diyAudio Member Join Date: Oct 2006	There are several issues to contend with: tube impedance, how much signal is bled through, and sending audio through the cable to the switch. Relays solve a lot of problems and allow channel switching without "tricks", which is why they are used. The Super Twin Reverb did use a foot switch to change the bias point of a preamp tube to move it into distortion. Unfortunately, most people did not like the tone.