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Passive Switch Box Schematics


al heeley
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I've tidied up my collection of passive switch box schematics and pasted them all together, hopefully these may be of use to people who want to have a bash at wielding a soldering iron and put one of these incredibly useful boxes together themselves. Just need good eyesight to unravel my pixel-art.

Passive Switch Wiring

9V battery powers the LED indicators thru a 2k resistor

Uses combinations of 3PDT and DPDT switches

X-grounding for noise suppression where appropriate

Where not indicated, jackplug earths are grounded out together

1. A/B switch allows switching between 2 inputs into one output (eg: switch between 2 guitars in a gig without having to unplug) or use in reverse with one input switching between 2 outputs, eg: 1 guitar into either of 2 amps or amp/tuner, or select pedal chain or bypass for example.

2. A/B/Y switch allows AND/OR config: one guitar into either amp A OR amp B OR both at same time.

Note: Can be used in reverse as A/B box but not recommended for 2 inputs simultaneously into one amp - guitars will interfere and cause hum.

3. A/B+X/Y switch allows A or B choice on input and X or Y choice on output, for example, choose one of 2 guitars on stage into one of 2 different amps, 1 of 2 guitars into either amp or tuner (will mute amp)

4. A/B/C switch allows one of 3 guitars into 1 amp or in reverse, 1 input into either of 2 amps or a tuner for example. Switch 1 chooses between A and (B or C). Switch 2 chooses either B or C.

5. Feedback/Loop switch selects to either bypass or route signal thru an effects box with option to blend some of the 'wet' signal back into the effect loop (level set by 250k pot) or leave it 'one-pass'.

switching.jpg

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There's some cool variations on a theme, I like the A/B/C one in particular.

On question, though: since the LED power supply ground and signal ground are common, isn't there a possibility that you could get a POP when switching? I personally like to keep LED ground and signal ground seperate in passive devices like these to avoid that *potential* problem...

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There's some cool variations on a theme, I like the A/B/C one in particular.

On question, though: since the LED power supply ground and signal ground are common, isn't there a possibility that you could get a POP when switching? I personally like to keep LED ground and signal ground seperate in passive devices like these to avoid that *potential* problem...

Cheers Paul, I built them all and tested them; i use a couple when gigging - they don't pop on switching. Maybe if an amp doesn't have earth lift switch, they would benefit from complete isolation on the power + LED's, but I've not yet heard any issues with any of these schematics.

My favourite is the A/B + X/Y - I use it at every gig - keeping 2 basses plugged in and the outputs going to either amp or tuner.

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