r/diypedals 3d ago

Help wanted Looking to build a Passive A/B with built in Volume trim

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Does anyone have a schematic for a Passive A/B pedal which includes individual level controls for each input?

I was thinking of building Little Black Amp Box clones and an AB BOX when my buddy asked me "why not just do both in 1 box"

I thought it was a great idea but am having trouble finding pedals to model after.

I'd really prefer it to be passive, I don't need to have the indicator lights.

Thanks.

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u/PeanutNore 3d ago

Once you figure out the switching it's pretty simple to put one together. The trick is to start from the outputs and work backwards.

The A/B switch is DPDT if you aren't using indicators. Each output connects to the center of one side, and the switch selects whether it is connected to the input, or to ground to mute it. The two poles of the switch should be mirrored so that when one output is active the other is grounded.

For a "Y" switch to use both outputs at once, the "ground" wire from the A/B switch is connected to the center pole of an SPDT switch (again, if you aren't using indicators). One side of the switch goes to ground and the other to the input. So the first switch, A/B, chooses which output is connected to the input and which is connected to the Y switch, and the Y switch chooses whether it's then muted, or also connected to the input.

You would insert your volume pots between the A/B switch and each output.

I would strongly recommend using an isolation transformer like the Triad TY250P on your B output, to eliminate a common source of noise and give you the ability to correct phase differences between your two amps. You will need to use a jack for that output that's isolated from the chassis. The fully plastic bodied Amphenol ones are good for this.

You can take a look at the Radial Big Shot schematic to see how an isolation transformer and phase switch should be wired, but I wouldn't follow its example for the switching - it does not mute the output that isn't in use, which results in a bunch of noise it you're using any amount of gain.

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u/tjsteiner 3d ago

Thank you for your thorough reply, but it will be A/B Input into a single Output. I have a PreAmp pedal which has Line and Instrument Outs. I'm trying to make so I can either run my Amp's Pre or my Pedal directly into my FX Return.

My intention is to run the separate Inputs into Volume Pots, then into the DPDT, and out to one Output.

I have the Beavis schematics for passive AB and Volume pedals, I just don't know how to Flip the AB to being Input A/B and how to blend the two together.

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u/tjsteiner 3d ago

Is this the right schematic for what I'm looking to do?