Help creating Mid control pedal

Started by tjdracz, June 10, 2014, 12:48:58 PM

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blackieNYC

I'm having trouble with this.  Coincidentally, mine sounds like that graph looks - very little boost.  I suppose RG is saying .033 and .01 for 1 and 2 is around a 400 to 1khz range, so I've tried that.  This should give 14 dB of gain? With the Q narrow?  I'm missing something. 
The notch will be narrow when the resonance pot is zero ohms, yes?  And the boost happens when the boost cut pot swings the resonant circuit over to the inverting input, right?  I'm looking for a fixed-wah sound, maybe a little less peaky, but I seem to be far from it.
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blackieNYC

Now I'm getting the boost and the thing seems to behave just like it should but - it goes into oscillation if you look at it funny.  Byproduct of being in the breadboard, combined with a high Q?  Or is there some thing I should be doing to stop the oscillation? Circuit is just as drawn, with .022 and .01 uf caps.   But at least I finally got some gain out of it- didn't change anything. Bad connection somewhere. 
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tjdracz

Quote from: blackieNYC on June 26, 2014, 12:04:50 AM
Now I'm getting the boost and the thing seems to behave just like it should but - it goes into oscillation if you look at it funny.  Byproduct of being in the breadboard, combined with a high Q?  Or is there some thing I should be doing to stop the oscillation? Circuit is just as drawn, with .022 and .01 uf caps.   But at least I finally got some gain out of it- didn't change anything. Bad connection somewhere. 

Haven't done it yet so can't say too much about that. Oscillation might be just breadboard really and lack of shielding. Try to add 47p cap or so between non-inverting input of first IC and the ground. I did that to avoid boosting very high frequencies. Try that and see whether it changes anything

blackieNYC

#23
I took care of the oscillation, by making these changes via Sabrotone:

a couple 150pf caps, resistor on output, 10k series resistor instead of 2.7k. I stayed with 9v single power and a single band eq, and I've heard no clipping at full boost and high Q. It hasn't broken in to feedback - been an hour or two.  I will update this entry after I have used it for a few hours just to be sure, but this is the fix.

Now to get a 40106 LFO to drive a vactrol instead of the frequency pot...
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