Ultra simple amp/cab switcher.

[Annette1954]

Hi there.

I would like to make a simple switch box to allow ONE OF THREE hybrid guitar amplifiers to output to ONE speaker cab.

Preferably using a rotary switch with three inputs and one output.

Annette

[GibsonGM]

Hi Annette, mike from the other place, who sent you here Welcome!

I'm sure someone more knowledgeable than I will chip in soon; they have done this before.

I am only concerned about finding a rotary switch or what have you that can handle your 25W amp head. 

[Annette1954]

Blah

[GibsonGM]

Blah?  Well, just get a radio shack 2 pole, 6 position rotary switch and do it, and hope it doesn't fail open, destroying your amp. Or spend the money to get the right switch box, it's that simple.

[Ben N]

Hi, Annette. What do you mean by hybrid? SS pre/tube power, tube pre/SS power, or something else? This matters because you absolutely cannot remove the load from a tube power amp without really bad things happening, many SS power amps are just fine without a load, or at least so I have heard.

Years ago Randall Aiken had posted a 2-amp head switcher on the DIY section of the Aiken Amps website, but he took it down because he didn't want to be responsible if someone who didn't know what they were doing mucked it up. Worked with relays, and fed the unused amp into a dummy load. I wonder if that can be found anywhere. Using logic or a microprocessor, I'm sure that could be updated to 3 amps with a rotary switch. Probably more than you need for SS power amps.

Edit: Here is Aiken's design: https://web.archive.org/web/20030718021444/http://aikenamps.com/HeadSwitch.pdf

[GibsonGM]

The trouble is finding out the easy way which SS amps can tolerate not having a load, vs. those that require it. 

[r080]

Still not super simple, but it seems like the Aiken switcher could be scaled up to 3 by using a rotary switch or even a cleverly wired DPDT On-On-On to trigger the relays. I think that would mean you would need each relay to have its own dummy load for when it is not connected to the speaker.

[Ben N]

Still not super simple, but it seems like the Aiken switcher could be scaled up to 3 by using a rotary switch or even a cleverly wired DPDT On-On-On to trigger the relays. I think that would mean you would need each relay to have its own dummy load for when it is not connected to the speaker.

You would need at least two, yes, assuming you make the switching clever enough, since two amps are not connected at any given time. But if it's possible to have no amps connected to the speaker out, then, yes three dummy loads. Grounding the inputs limits the heat dissipation needed by dummies on inactive amps.