Cute switching trick - limited applicability

[Mark Hammer]

The PAiA Gator uses the envelope from the input signal to provide a control current to a 3080, with some lag added to it to slow down turn on time.  The stock circuit uses a SPST switch to "bypass" the effect, by connecting the op-amp supplying the Iabc control current directly to +9v.  It's not an actual bypass of the circuit, but a disabling of the effect.  the signal runs through the entire circuit in effect and bypass mode.  http://gaussmarkov.net/layouts/gator/gator-schem.png

Of course, when there is no status LED, how do you know which mode it is in?  You don't want to be monkeying around with switching back and forth to determine if you simply don't have the sensitivity up high enough or the battery/circuit is dead.

Here's what I did.  Bypassing the effect connects the circuit up to +9v, and disconnects +9V when the effect is engaged, so you have +9v running to your footswitch anyways.  I popped in a SPST switch, and tied +9v to the common.  When the effect is bypassed, that +9v goes to pin 6 of IC4b.  But when it is engaged, the +9v is now redirected to an LED and current-limiting resistor to show thatthe effect is engaged.

Neat, huh?  As the title says, though, there are limited contexts where this can be employed, but it works great in this one.

[joegagan]

nice thinking. i like that sort of solution.

[Mark Hammer]

Thanks.  What also worked out great for me was that I had the Gator in a fairly low profile box, and also had a shallow profile Carling SPDT that fit nicely between the chassis top and PCB.  I still had to eliminate the hex nut on the underside of the chassis to clear the board, but managed to fit it in.  Given the size of the PAiA layout, would have needed an entirely different chassis to stick a 3PDT in there.

[PRR]

> I popped in a SPST switch

SPDT ??

[Mark Hammer]

Yes, correct, SPDT.