[sdiy] Center Detent dead zone on an "attenuverter"?

Donald Tillman don at till.com
Sun Apr 3 01:15:19 CEST 2016

> On Apr 2, 2016, at 1:50 PM, Chris McDowell <declareupdate at gmail.com> wrote:
> I can link to a pic if needed, but the circuit is straightforward and many of you are likely familiar: Input goes through a 100k to the wiper of a pot, two inverting amplifiers are in series, with the one leg of the pot going to the first inverting amp, and the other leg going to the second inverting amp

Not straightforward.  (Of course!)

Having that 100k resistor in front of the pot makes the system more sensitive to the very problem you are seeing.  Instead, use two 100k resistors, one on each end of the pot.  I don't know the pot value, but you do, so you can calculate the effects of, say, a 10% asymmetry in pot resistance for both situations.

If it's still a problem, I'd recommend adding two resistors, one from the wiper to each side of the pot.  This will change the curve of the control, which may be a feature in this situation, so that the gain will be lower in the center and grow at the extremes of pot rotation.  Adjust the resistor value to taste.

  -- Don

Don Tillman
Palo Alto, California
don at till.com

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