ASM VCO

[Joachim Verghese]

On Fri, 28 Jun 1996 Paul.Maddox at bew.co.uk wrote:

> 	1) Can I decrease value of cap (on the
> integrator) to increase the speed of the VCO?
> I want to run the VCO 16 times faster that it 
> the tone I want to generate, Im trying for
> basic wavetable stuff here.

I haven't tried this myself on a sawtooth-based VCO. You may run into
linearity problems since the sawtooth retrace time becomes significant
at high oscillation frequencies. I'd recommend using a triangular-based
VCO for this application.

> 	2) The long tailed pair of trannys
> Gene suggestes matched 2n3904's, and he uses
> a MAT02 in the PCB, WIll any matched pair work?
> Ive found a chip (EN2016) claiming to be similar
> to the 2n3904 (except theres four matched trannys
> on it), Will this device work?

The EN2016 would probably work well (except for the fact that it won't
fit into Gene's PCB). 2N3904s work well too, as long as you provide
adequate *thermal coupling* (simply glueing them together isn't enough),
you don't even have to match them for this application.

> 	3) I also take it that the sync in can
> be driven directly from the pulse out of another
> VCO, am I correct, or just plain loopy?

Any waveform with fast negative-going edges will work.

-joachim