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I'm trying to find a solution for the following problem: I have a RETURN section of a circuit that has to mix a DRY and a WET audio signals. The circuit is Stereo.

The tricky part is that i want the DRY signal to remain unaltered and not-attenuated until half rotation of the knob, and then it decreases.

Example: I leave the RETURN Pot at 12 O'clock. I can play with the SEND and add it to the DRY. Now i turn the RETURN counterclockwise and. IF the RETURN pot's curve is normal, the DRY signal will have a change in volume (a little bit louder). IF the RETURN pot's curve is like the one I'm looking for, then i won't hear any change in volume on the DRY.

This idea Is different from a simple summing amplifier solution since when the pot is at clockwise position, only the WET will be heard, at counterclockwise position only the DRY will be heard and at 12 o'clock both can be heard BUT the DRY remains 1:1.

If a Quad-gang MN Taper (blend/balance) would exist, this would be straightforward and would avoid lots of headache but this doesn't exist.

I could buy a linear Quad-gang potentiometer and mess with the carbon resistive trace (i.e. adding special conductive paints to short half of the track) but I don't think is an ideal solution, since It would be probably last a short time and is also quite time consuming.

Do you have any hints or do you think is possible to achieve somehow?

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  • \$\begingroup\$ Can you use something like VCA or OTA amplifiers and tailor the control voltages to do what you want? \$\endgroup\$
    – GodJihyo
    Aug 11, 2023 at 19:11

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You might look at using voltage controlled amplifiers (something like this for example) or operation transconductance amplifiers (example here) along with a circuit to generate control voltages to give the desired results. You might be able to use an available MN pot to get the control voltages that could then drive two sets of VCAs to get stereo without needing a quad pot.

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  • \$\begingroup\$ i used a LM13700 in the past with bit of struggle. First, the internal buffer always caused issues. At some point I just started to use normal Opamps as buffer instead. Secondly, i found out that most of the time it was picking up interference/noise and overall, even using the linear. diodes, it was not really clean or THD-free. In general, I wouldn't choose that for an high precision audio circuitry. What is your opinion on it? Do you have experience with those THAT VCAs? they are a bit expensive but they look good at first glance (0.05% typ dist.). \$\endgroup\$
    – nhouse
    Aug 11, 2023 at 20:30
  • \$\begingroup\$ @nhouse I've only used the LM13700 to make things like voltage controlled oscillators, nothing where I was worried about high fidelity. Haven't tried the THAT VCAs, they look promising though. They're supposedly used in a lot of pro audio gear. I think I actually bought some a few years back but never got around to trying them :| They do list faders and panners as some of the applications for them so I thought that might fit what you're looking for. There may be other brands of VCAs that would be better, IDK, these are the ones I'm aware of. \$\endgroup\$
    – GodJihyo
    Aug 11, 2023 at 21:09
  • \$\begingroup\$ i bought some AS2164 (quad VCA) to try and will buy and test THAT 2162 as well. Will report as soon as i will try them \$\endgroup\$
    – nhouse
    Aug 11, 2023 at 22:17

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