Is this circuit (a modified DOD 440) biased wrong, or is it just wrong?

Started by Josh?, August 14, 2018, 07:33:22 PM

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Josh?

Hi everyone!
I'm trying to build my own DOD 440, but I'd like to replace the filter with a state variable filter (see the Wikipedia page: https://en.m.wikipedia.org/wiki/State_variable_filter).  I've breadboarded it up, and all I'm getting are some very low volume distorted notes, with no filter sweep.  This leads me to guess that I biased one or more of the op amps in filter wrong, but I'm not sure. Here's the schematic for what I have on the breadboard:



Does anyone notice anything wrong?
Thanks!

Josh?


MaxPower

The points labelled HP, BP, and LP (in the wiki example) are the outputs for each filter section. You need to go from those points to the output(s).

Google state variable filters and check the images. Maybe the other schematics will make things clearer as they are drawn more logically (imo) and are labelled better as well.
What lies behind us and what lies before us are tiny matters, compared to what lies within us - Emerson

Josh?

Oh my bad I didn't include the output on my drawing, so sorry.  I've tried both the band pass and low pass outputs through a capacitor, and there's no real tonal difference between the two that I can tell.

Mark Hammer

That's not a "modified DOD 440"; it's a Mu-Tron.  I think you'll find more useful information by approaching it as that.