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

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Apr 2 23:07:56 CEST 2016

Hi Chris,

As a user, or designer, I'd prefer to see separate controls for gain and invert so that the gain is not so touchy. With a single gain knob, you can be assured that fully counter-clockwise is a gain of zero instead of worrying about the accuracy of the pot's calibration. This would require a second switch unless you can find a pot with a push-pull switch.

I'm reminded of the Technics SL-1200M3D "reset" button that completely turns off the pitch slider, which also fixes a previous problem where the center detent did not match +/-0 pitch. The other models have an automatic switch associated with the center detent that actually engages a defeat circuit, but it was difficult to calibrate the slider so that the center matched the defeat, or reset, setting. I realize that what I'm suggesting would require an additional switch unless you can find a center-detent pot that also has a switch on the center detent. But, as I started, I think it's better to avoid the problem completely by placing full attenuation at the left and separating the invert function.

As for diodes, those are fine for DC control voltage signals, but I wouldn't put audio through back-to-back diodes! You didn't say, but I assume your 4-channel mixer is for CV, not audio.


On Apr 2, 2016, at 1:50 PM, Chris McDowell <declareupdate at gmail.com> wrote:
> I have a very simple 4 channel mixer that has "attenuverters" (gain from -1 to +1) on each input. As it stands, the "off" position is super narrow and not exactly in the vertical position of the pot. Both of those were expected, and it's fine for anything that doesn't need to be silenced. Using a pot with a center detent leaves tiny bit of gain one way or the other, since the pot and summer resistors aren't exact. So, I wonder, is there a reasonable method of adding a dead zone to the center of an attenuverter like this, without trimmers? 
> 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. 
> Initially I thought to myself "yeah easy, back to back diodes like on a pitch bend wheel" but about 1 second later realized that it's not at all the same situation. Back to back diodes on the output would have the desired effect when the pot was centered, but would not with any gain applied. 
> Any pointers appreciated! Thanks,

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