Looking for Study Material: Dual Footswitches for Bypass and Modulation

[turdadactyl]

Can anyone think of a schematic (or several) I can look at to wrap my head around the wiring I'd have to do for a pedal with 2 footswitches and 2 LED's?  I'd like to understand the circuit layout where one 3PDT is the bypass and controls an LED to show the pedal is on, and the second 3PDT (I think it would be a 3PDT) would control an optional part of the effect, such as modulation, and a second LED.

Example: A fuzz/vibrato pedal that has one FS to turn it on and a second FS to take the vibe in/out of the circuit.

Thanks!

[nocentelli]

It will depend on how the effects are implemented: In your delay with switchable modulation, the delay switch would normally be a master true bypass switch (search for "3PDT true bypass"), but the modulation switch might just be a SPST to make/break a single connection within the delay circuit, I.e. connecting or disconnecting an LFO from the delay pot. If you wanted an LED to show modulation on/off you would need another pole to switch that.

In your hypothetical vibe/fuzz pedal, assuming the fx order is fuzz->vibe, you would probably need a 3PDT master true bypass that sends the signal to the fuzz, with the output from the fuzz going to a second true bypass 3PDT that can bring the vibe in or out; The output of the vibe bypass switch would then go back to the fx return on the first master bypass switch.

If you post schematics or links to the circuits you are planning to work with, people can add more specific advice

[turdadactyl]

Thanks.  That's good info to digest.

One that I'm definitely planning to do this with is the Tim E. PWM, which I mentioned in another thread:
http://www.diystompboxes.com/smfforum/index.php?topic=114195.0

That said, I started this thread rather than just pursuing it there because I'd like to fully understand it, rather than just make it work.  Another example that I just looked at is the Ugly Face with LFO, but I'd say that's probably pretty darn similar.  I would almost certainly use an LED on both FS's so if the pedal is bypassed I'd still know if the optional part was on before I turned the pedal on while playing with it in a real situation.  But again, understanding the difference is my goal.

Some possible uses for this, off the top of my head:

• Dist/Fuzz/OD with optional octave or swell
• Something like the BYOC Analog Vibrato

Here's a schematic on the Ugly Face with LFO
http://www.cad.rs/d/UglyFaceLFO.pdf

[turdadactyl]

In case anyone else is following along or finds this in the future, this was pretty idiot-proof reading from my perspective.  Not all the way to where this discussion was headed, but useful.

http://www.coda-effects.com/2015/03/3pdt-and-true-bypass-wiring.html

[nocentelli]

The PWM just needs a make-or-break to connect or disconnect the collector of the transistor to pin 3: The transistor's collector-to-emitter pathway acts like a variable resistor to ground, with the actual resistance being varied by the LFO acting on the base of the resistor. This variable resistance is in parallel with the PWM pot's resistance to ground, so it's a bit like wobbling the pot around manually.


For the Uglyface with LFO, the switch that cuts between either the LFO or envelope control of the filter-y effect is actually shown on the schematic you posted, but it's a DPDT - If you want an LED, you need one more pole, so you'll need a 3PDT as shown.

[turdadactyl]

Love this forum!  Thanks again.