Channel switching options

[bieworm]

Hey guys

I am trying to draw a schematic for a dual channel amp. I intend to switch between clean and OD with relays.
I drew 3 scenarios for the switching and wondered which one would be best. Maybe there is another method I didn't think of, so I'd be glad to hear that too...

I'd be adding reverb too between preamp and PI, so I need to enter the PI at 1 side with both channels.
I would like to avoid pop at any cost..

thanx

2204 - Clean switching.png_thumb.png

[pompeiisneaks]

It should even be simpler than that. You can just omit the first relay and use scenario 2. I.e. let both channels work with the input signal, BUT dump one to ground and let the other pass.

~Phil

[pompeiisneaks]

Actually if you wanted to, most relay's I've seen are DPDT, so you could literally still use 1 relay, and have half of it switching the input side, the other half switching the output to the mixing resistors. i.e. if you're on channel 1, then it selects input 1 on one side and sends output of channel 2 to ground. A bit more complex, and not mandatory, but... another option.

~Phil

[bieworm]

I get the part of the output. Thats how I drew scenario 2. But I don't get the input part. I'd have to connect the input wire to both terminals and the common to ground. Isn't the input signal going to ground in both cases, following the shortest path to ground? Or should I do something additional?
Believe me.. I would love to use only one relay, because I already need a second to switch the tremolo. So I'dbe glad if this was possible.

20210223_202426.jpg

[bieworm]

It should even be simpler than that. You can just omit the first relay and use scenario 2. I.e. let both channels work with the input signal, BUT dump one to ground and let the other pass.

~Phil

I tried that , but both channels seem to interact unpleasantly. But I must admit they share V1a in that circuit. Might be different with 2 separate dedicated first stages..

[romberg]

If I'm not mistaken, the clean channel and OD channel here will be out of phase. Clean has two gain stages and OD has three (the cathode follower won't flip the phase). So, you don't want to mix them.

I'd go with Phil's suggestion of sending the input to both channels. It won't hurt anything. Then use a single relay to switch before the PI. One half of the relay would send channel A or B to the PI. The other half of the relay would ground the output of the opposite channel. The extra relay on the front end seems like it would just complicate things.

I do something similar in my "marshall" which switches between 2, 3 and four gain stages. In reality all the stages are on all the time. I just tap into the output I want and ground the outs not being used.

Mike

[bieworm]

If I'm not mistaken, the clean channel and OD channel here will be out of phase. Clean has two gain stages and OD has three (the cathode follower won't flip the phase). So, you don't want to mix them.

I'd go with Phil's suggestion of sending the input to both channels. It won't hurt anything. Then use a single relay to switch before the PI. One half of the relay would send channel A or B to the PI. The other half of the relay would ground the output of the opposite channel. The extra relay on the front end seems like it would just complicate things.

I do something similar in my "marshall" which switches between 2, 3 and four gain stages. In reality all the stages are on all the time. I just tap into the output I want and ground the outs not being used.

Mike

In that philosophy shouldn't it be better to switch the unused channel to ground after each 1st stage? Then there is very little signal going through each unused channel?

[romberg]

In that philosophy shouldn't it be better to switch the unused channel to ground after each 1st stage? Then there is very little signal going through each unused channel?

This may or may not be better. It depends. If your layout and wiring is such that there is stray coupling between the two channels such that they unintentionally interact when both are active, then yea. Shutting down the unused circuit would be better.

However running an extra ground wire from your switching relay back to stage one of each channel is more messy than just grounding the outputs (which are already right there at the relay). If it were my build I go with grounding the outs. Then if that did not work I'd try and cleanup my lead dress and or run extra grounds to after stage 1 of each channel. I would make it simple first and add stuff (extra wire runs) if needed.

Mike

[bieworm]

In that philosophy shouldn't it be better to switch the unused channel to ground after each 1st stage? Then there is very little signal going through each unused channel?

This may or may not be better. It depends. If your layout and wiring is such that there is stray coupling between the two channels such that they unintentionally interact when both are active, then yea. Shutting down the unused circuit would be better.

However running an extra ground wire from your switching relay back to stage one of each channel is more messy than just grounding the outputs (which are already right there at the relay). If it were my build I go with grounding the outs. Then if that did not work I'd try and cleanup my lead dress and or run extra grounds to after stage 1 of each channel. I would make it simple first and add stuff (extra wire runs) if needed.

Mike

Thanks Mike