Capacitance of switches

[92Volts]

I just tried a simple proof-of-concept channel switch. A dual-toggle hooks the master volume either to the end of the preamp (overdrive) or after the first gainstage (clean). Used one half of this switch: https://www.parts-express.com/dpdt-mini-toggle-switch--060-338

It switches, but the high-gain signal bleeds into the clean... a lot! It might be better if my clean "channel" was a fully-built preamp (right now it's lower volume than the overdrive), but I think it would still be a problem.

I assume the solution is to use the other half of the switch to cut signal to the unused channel, either by rerouting or grounding something.

But do I need to worry about housing low-level signals in the same switch? Let's say I had 2 separate preamps and want to route raw guitar into one or the other, and pull signal from the end of the active one. Can I handle the raw guitar signal in the same DPDT switch as "hotter" signal or am I asking for feedback?

I guess part 2 of my question is when people buy relays to do this with a footswitch, what considerations go into choosing a relay?

[sluckey]

You're just asking for trouble when you put a very low level signal on one side of a double pole switch and then put a much larger version of that same signal on the other side of the double pole switch. Not just the switch itself but the routing of those signal wires. The proper solution is to use two relays or vactrols, or other opto-isolator switches and place the switching devices very near the circuit to be switched so that there are no long signal wires involved. Then you can use a simple SPST switch to switch a dc voltage to control both of the devices. There are plenty of common amps that sucessfully do what you want. Study some of them.

[92Volts]

It makes sense that those lines shouldn't be routed through the same device. A bit of a bummer that it requires more parts but in some ways, this "should" simplify the layout (definitely makes for a better/quieter layout).

PartsExpress only carries DPDT relays (except for some bulky automotive types). I'm sure Mouser has smaller SPDT relays, but their site is a pain to navigate. Am I likely to find an SPDT cheaper than like $4/each, or is it typically cost effective to have a DPDT and leave half unused?

[DummyLoad]

https://www.mouser.com/Electromechanical/Relays/Low-Signal-Relays-PCB/_/N-5g38?P=1yvsbatZ1yvsbasZ1yvsb9yZ1z0x3td

[DummyLoad]

just wire 1/2 of the switch, or just use a DPDT and wire in tandem if the spare contacts are a noise source - i usually just ground the common leg of the unused switch or that 1/2 to to mute the other channel.



--pete

[sluckey]

Look at how Hoffman wired the switch in his Plexi "Hot Switch" mod...

     http://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf

[92Volts]

Thanks for the Mouser link and advice, DummyLoad!

slucky, that looks VERY similar to what I'd been thinking about, including sending high/low signal through the same switch! My understanding of why it works here but not always is:
*Kills signal through extra stage when bypassed
*High/low signals out-of-phase when both are present
*Wires for in/out of one gain stage are nearby in the layout anyways

So for all those reasons, you may get away with bypassing some small portion of a preamp like this, but separate relays are preferred for true separate channels, especially if they're switched early (like the raw input)?