A different kind of A/B box... (AutoSwitcher)

[trad3mark]

Hey all,

So i found myself needing a sort of switcher. Basically, i think what i need is something based on a comparitor. Allow me to explain the situation.

lets say you take two signals:
1. Normal Guitar Path. Guitar > OD > Fuzz > Output
2. Theremin. Theremin > Boost > Output

Now what's important to note here is that the theremin has no signal input. It only outputs sound when you start making silly noises with it. So, what i'm looking for is some sort of a switcher that has 2 inputs and 1 output, but, it'll only output whatever signal has the higher output. So lets say I'm playing my guitar and then i want some theremin, i can just theremin away and the box will automatically switch the output to the thremin.

I suspect this can be done with a comparitor chip. If it can be balanced that the output (or at least what the comparitor "sees") of the theremin is higher than the guitar path, then the comparitor can switch the output from the guitar path to the theremin path.

Anyone care to help me out on this one? or at least clarify if that's what i'm looking for?
cheers

PS. Now that i think about it, that could be cool to pair up with something like a Kaossilator... mmmm....

[Hides-His-Eyes]

You could try rectifying and smoothing the two signals to run them into an op-amp comparator, but it'd be a tricky business getting the response time about right.

A far cruder method would involve two 386s driving LEDs, that were rolled with LDRs in a voltage divider setup.... Not sure I'd recommend that though,

[joegagan]

the toadwaorks enveloop could probably do this. a very under-appreciated pedal in my opinion. once again, proving that the public wouldn't know a good product if it hit them in  the head like a carp.

[Hides-His-Eyes]

Devi ever had a similar box, that I think again wasn't 'run with' because people have no imagination

[Gurner]

this kind of thing 'screams' PIC, but I doubt you'd want to learn all about PICs for just this one need!

To keep it analogue, this is the way I'd approach it...

Guitar->preamp-> peak detect cct-> into a comparator +ve pin
Theremin-> preamp (if needed)- peak detect cct->into comparator -Ve pin

So long as the rectified guitar signal is greater than the theremin (which it would be all the time except when you start playing the theremin), the output of the comparator will be high, start playing the theremin...this increases the voltage on the -Ve pin (and since you aren't playing the guitar - unless you are ambadextrous?) the comparator negative pin will then be higher than the +ve pin, the comparator output will flip to low.

Use the comparator high/low output to then toggle an anlogue 'switch' of your choosing.

PS How did your sustainer turn out ? 

[R.G.]

Noise gate and logic.

Noise gates other than downward expanders have some subsection which detects signal level and does something when the signal is above or below a threshold. In the case of a noise gate, that is to mute the output when the signal is below X, which may be fixed internally or adjustable. No reason to not use the logic signal to do whatever else you'd like it to do.

So one thing is you could use the level detect output to turn off the normal channel and turn on the theremin output. It's kind of a noise gate on the theremin plus a side signal that turns off the normal channel when it turns in the theremin.

There is a lot of what I think of as good housekeeping and hygene to be done to make it operate quietly and effectively and only when you want it, but that's the general idea.