Help needed: DYI Amp head switch box- 1 Cab + 1 Load box

Catthan

Hey there,

I'd like to make me a switch box so I can run 2 heads into 1 cab.

The head not used should get connected to the load box.

So i'm thinking 2 inputs (amp 1 & 2) and 2 outputs (1 to cab & 1 to load box)

I'd like some help with what should be inside box.. Some type of relay??

Any help would be appreciated.

Thanks

Gassage

There are a couple on the market...radial and Palmer make them

Catthan

Thank you @Gassage, I'm aware.

The purpose however is to built it myself with the help of the el. engineers we got at work. 

That's if it doesn't involve any sophisticated pcb designing etc; we could still do that here but the guys have more important projects to design stuff for. For some reason I've been thinking this should be an easy job tho..

ICBM

It's not that easy if you want to do it on the fly, because you have to suppress the signal through the speaker circuit while the switching is taking place - even though it's only for a fraction of a second, this can cause arcing and damage with some amps - as well as controlling the input signals to both amps to make sure the unused one isn't simply blasting away into the dummy load, which is not good for the valves. The good news is that muting the unused amp means the dummy load can be small and is only there to suppress possible instability - it doesn't have to be a full-size load box which can handle the full power of the amp.

So the signal path needs to be:

Input > switching device > inputs of both amps

Speaker outputs of both amps > switching device > (probably internal) dummy load and output to speaker cabinet.

Getting the switching mute just the right length to protect the amps without causing an audible drop-out might be tricky too.

Catthan

Thanks @ICBM, what you said about suppressing the signal and arcing is very useful info which I hadn't thought of. I'm wondering whether there's an off the shelf component that does this.. I guess that's what the time overlap means in the radial cabbone blurb.. 

RE a load, I was thinking to use the Koch one I have externally, so it outputs on the switching device, 1 to cab and 1 to Koch.

ecc83

I built one of these a couple of years ago but found it difficult to get quiet muting of the amps.

I solved this by running the guitar through a buffer (a rather good one!) and this allowed switching at a low Z.

I did not investigate them but FETs as mutes might work ok.

My unit was powered from a 16 volt, 800mA line lump. Guess why!

Dave.