Potentiometer Wiring Question

I have never worked with dual ganged pots, and some of you already know I’m kind of a dunce when it comes to pot wiring (@ChristianBloch :joy: )

I am working on a small stereo mixer for the small circuits that I use and would like to conserve space by utilizing dual ganged potentiometers


I am curious if I have the wiring correct on the pot (top center)

Thanks in advance for any help!

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If you are aiming at a mixer consisting of inverting opamps, then as a consequence the mixer will invert the phase of whatever signal you put into it. If you don’t want that, then add an inverting opamp to each output with a gain of -1.

1: the 1 mu decoupling capacitors should be connected between the inputs and the attenuation pots

2: the + inputs of the op-amps should be connected to GND.

The amplification factor of the op-amps is now about -3.

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In my experience, pinouts of dual gang pots are inconsistent. When they are just two parallel rows of three it’s easy, but it gets gets confusing when it’s a row of five, for example. I usually bust out the multimeter to find out what’s up.

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this is based on an already working schem designed by Pugix (Richard Brewster) for ciat-lonbarde ultrasound filters, AVDogs and Gongs Filters - I did not design this circuit entirely, just made it smaller since I will not be using 12 filters like in his.


The Filters in question are these -

@Jos - so at the point of R Out and L Out - you are suggesting a second tl082?
Why run the +'s to GND? (please help me understand :slight_smile: )
Some of these designs are above my head lol, I am still learning!

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Yep, a 2nd TL, one op-amp for each output, if you aim at a mixer that does not invert the phases, otherwise you can leave those out. The +inputs to GND make that the opamp makes a virtual GND at its - input because an opamp with a feedback loop (resistor connecting output and - input) will try to reduce the voltage difference between its -input and +input to zero. If it succeeds, and it will, the -input will get the same voltage as the +input, thus the -input will become 0 volt, so is virtually connected to GND. In that condition you can calculate the resulting output voltage as the ratio of the input the feedback resistor and the resistor connected to the input (times -1) times the input voltage. More details here.

The capacitors in their original position decouple the inputs from the opamp, but not the inputs from one another because they are connected to one another via the potentiometers and resistors at the input stages of the mixer. So a DC value on input one would also in part be connected to the other inputs (and the outputs they get their voltages from). You may ask yourself whether that is what you want.

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