A/B switch with volume

All frequent questions on switching: true or not true bypass, transistor-based or mechanical.

A/B switch with volume

Postby daithibailey » 29 Jul 2012, 14:44

Hey, completely new to this lark. Has anyone got an answer, or can anyone point me in the right direction. Basically have some bits and bobs that i want to put together to make a passive a/b switch with a volume control on one of the outputs. Was pretty much following this: http://www.generalguitargadgets.com/pdf ... a841b3e85a and putting a volume control between the switch and output2. I was also just using a dpdt instead of a 3dpdt. But no sound at all when i plug in. Is it just bad wiring or have i got something fundamentally wrong? ~Any help is much appreciated.
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Re: A/B switch with volume

Postby PokeyPete » 06 Sep 2012, 08:38

daithibailey wrote:Hey, completely new to this lark. Has anyone got an answer, or can anyone point me in the right direction. Basically have some bits and bobs that i want to put together to make a passive a/b switch with a volume control on one of the outputs. Was pretty much following this: http://www.generalguitargadgets.com/pdf ... a841b3e85a and putting a volume control between the switch and output2. I was also just using a dpdt instead of a 3dpdt. But no sound at all when i plug in. Is it just bad wiring or have i got something fundamentally wrong? ~Any help is much appreciated.

Your link is to a very simple A/B switch. Other than the LED's, there is no real circuit. When you're designing a stompbox
circuit, there are certain parameters that have to be met....like high input impedance and low output impedance. If you look
at the input of an old Fender amp you'll see a 1 meg resistor across the input jack. This is the impedance that your pickups
are expecting to see. Each stompbox should have a similar input impedance that mimics the amplifier input. The output
impedance should mimic the guitar's pickup impedance. My advice is to build the A/B switch exactly as it is, then have
output2 go to a simple, clean boost pedal. That way you would have a nice A/B box and all the volume you probably need
from ouput2. You could include the booster circuit inside the A/B box just in front of the Output2 jack. But it would require
a nice little amplifier circuit not just an attenuating pot to ground.
“No man is so foolish but he may sometimes give another
good counsel, and no man so wise that he may not easily err
if he takes no other counsel than his own. He that is taught
only by himself has a fool for a master.”
–Hunter S. Thompson
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Re: A/B switch with volume

Postby aquaboy1993 » 13 Dec 2012, 22:12

I made something similar to switch between 2 basses but to also attenuate volume on one. My passive P is much hotter than my active humbuckers. Don't ask me why. Might be the $20 preamp Dean uses.

For 2 inputs and one output, I connected one middle lug of the DPDT to the Tip of the output and the other middle lug to ground. I put an X of jacketed wire connecting the other 4 lugs. This grounds one input when the other is active and vice versa. I wired the Tip of one input direct to one lug of the switch. The other Tip I wired to lug 1 of a 100k pot. Lug 2 I wired to the other half of the switch (not on the same part of the X). Lug 3 I wired to ground.

If you are using 1 input and 2 outputs, change your wiring as such: connect pot lug 1 to the switch and pot lug 2 to the output.

Please realize, this will only CUT the volume of one of the options.

HTH,
Mark
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