Three Sisters ALL output gain adjust

One of the main reasons I got the Mannequins Three Sisters was for the triple self oscillating filters. Works great except the summed ALL output tends to distort (on my unit at least).

I decided to reduce the gain at the ALL out stage to prevent clipping. If you pull the surface mount board off the back of the unit, you’ll find a 30k resistor labeled R8 in the bottom right corner, which is the feedback resistor in an inverting summing stage. I tacked on a 47k resistor in parallel to reduce the gain.

I could have probably gone lower but that’s enough to tame most of the clipping.

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Nice work!
Id be keen to give this a go, would you mind posting some photos?

IMG_4915

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I tacked the through hole 47k in parallel with the SMT 30k just because that’s what I had. If you want to avoid the tack on, replace R8 with an 0603 resistor. Anything in the range of 10k to 18k should be fine.

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Thanks :sparkles::pray::sparkles:
I’ll be sure to have go sometime!

Wont this make ALL output too quiet when using three sisters for filtering/mixing purposes?

It drops the output by 4.4 dB, so it’s quieter but not by that much. If you were to sum the individual channels on a mixer and reduce the individual gains so you don’t get a clipped output, the result would be the same.

For reference:

It says TL074 here, but that’s actually a fancy rail-to-rail opamp so it shouldn’t clip before +/-11.5ish

NB: Please triple check that the backboard is correctly aligned when reassembling the module! If you attach it misaligned by 1 pin it can blow up all the 2164 chips and that is not a fun repair.

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