[sdiy] Electric Druid VCADSR filter hysteresis

[Tom Wiltshire]

Hi Jack,

I'm afraid that's a new one on me, and I've seen most of the ways that circuit can go wonky by now.

The filters just smooth the 0-5V PWM pulses coming from the PIC. When the envelope is off, the PIC should be outputting 0V, so there shouldn't be any way it could float off to +15V.

I'd check that the PWM output is ok - if you hold the Gate on, you can vary the PWM pulse width with the Sustain control. Pulses should be at 19.5KHz. After that, there's got to be something weird about your filter, since that's all that's left. What op-amps did you use? Any reason they might start acting like a comparator? What's the other input tied to? 

Regards,
Tom


On 1 Sep 2014, at 22:09, Jack Jackson <jackdamery at hotmail.co.uk> wrote:

> Tonight I've built Electric Druid's VCADSR circuit and it seems to be working fine except the opamps of the low pass filter lock at +15V when there is no input (or almost no input) from the PIC. This means they always have to 'jump' down to 0-5V when the ADSR is in use.
> 
> I've double checked my breadboard of the circuit and I can't see any errors. Any idea what I could have done wrong?
> 
> Best Regards,
> Jack
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