[sdiy] VCF schematic

[harry bissell]

Hi Charles...

imho there should be a small resistor in the input to the overload
comparator... as you have it the 1M will inject current back to the
summing junction of the input opamp as it changes states. Maybe by this
time you do not care. The series resistor will limit that current...

H^) harry

Charles Bisaillon wrote:
> Hi,
>
> The capstone VCF is a simultaneous LP/BP/HP with FM capabilities, variable
> input gain and input clip LED indicator. The design is alright, it has some
> quarks but they might come in handy at times. The Band Pass is the output
> that is the less reliable, it has lower signal than the other outputs when
> the resonance is off, but it's full of tricks with resonance full (I got it
> to imitate a Harley Davidson rhythmic pattern with a constant 50Hz square
> wave).
>
> I've also had a lot of troubles with the resonance circuit, it doesn't feel
> like it is a linear pot I'm turning, the resonance creeps in exponentially
> as I twist the knob. Choosing the right resistors was a big compromise game.
> I've tried many things but I reach my limit of understanding.
>
> There was also a lot of phase cancellation issues but I got most of that
> fixed, the only quark left from that can be heard in the high pass filter
> with high resonance, the volume suddenly drops a couple of dBs at a certain
> cutoff frequency.
>
> Anyways, I'm not too worried about this and other small things, the
> schematic is accepted, the VCF is considered finished.
>
> http://www.oveloe.com/490/vcf_sch.jpg
>
> Cheers
>
> Charles
>
>
>
>
>