[sdiy] Pitched Noise/VCO Bank Schematic Posted

[Scott Stites]

Hi John,
> LOL! I read your post this morning; fortunately, I saw the "Bissell!"
> comment when I was between sips of coffee. :-)
>
> The recordings of this VCO in action are cool (creepy1b.mp3 and
> gongcomp.mp3). Nice work.

Thanks!  Actually, the random fluctuating voltage was doing the most work
=0).

> Capacitors! Is that cheap enough? ;-) Perhaps you need something just a
tad
> more sophisticated.

Well, cheap enough for sure, and (as it is) it's not the most sophisticated
circuit, so that may work just fine.  I can imagine if one had to go to too
extravagent means to smooth out the square waves, the law of diminishing
returns would come into play.

I guess another low-tech approach would be to use another hand-full of the
cheapo (BGMicro cheapo, I mean) VTL5C2's and some quad FET op amps and make
VC lag generators.  Sort of like the Random Fluctuating Voltage, the Fc of
the lag generators could follow the CV and provide enough of a lag
throughout the freq range to smooth out the edges.  I guess, instead of lag
generators, one would at this point call them LP filters =-D.

BTW, I have used the VTL5C2 as a the resistive element in a VC Slew - it
works great (well, as great as a VTL5C2 does anywhere).

> You might talk to Scott Gravenhorst (I CCed him on this) about using the
> 4046 Phase Locked Loop chip, but that technique may be more suited to LFOs
> than audio frequency VCOs. But, it may be more trouble to smooth the
squares
> than to start over with (for example) sawtooth VCOs.

I hadn't thought of that - I've seen Scott's 4046 stuff, and it's been on
the 'to do' stack for a while now.

> Wish I had something more useful to add.

Quite useful enough, thanks!

Cheers,
Scott