[sdiy] 2164 expo VCO tracks!

[David G. Dixon]

> Do you think that the sockets themselves might have something to do
> with the HF crappiness? What's the capacitance and resistance of a
> socket? I think it's worthwhile to check it out.

I highly doubt it.  If that were the case, then the IC pin would also be a
significant factor.  Remember, the IC itself is a little tiny thing in the
middle of the IC package, connected to the IC pins with little tiny wires.
Where does it stop?  This is not that critical of an application.

> Out of curiosity - if you wanted to put in more decoupling, where
> would you do that?

Adjacent to the power pins of the opamps which are being used (partially) as
comparators.

> Do you think it's worthwhile to decouple different parts of the
> oscillator from one another?

I don't notice anything funny in my waveforms on the scope, even though, for
example, the sine shaper differential opamp is on the same quad IC as the
pulse wave comparator opamp, as is the reference current opamp and the saw
integrator.  I've understand that there may be some crosstalk between opamps
on a single chip, but I'm not seeing it.  The "crosstalk attenuation" of
TL07x, according to the datasheet, is 120dB.  That's 1 ppm.  Hence, one
wouldn't expect any effect between opamps on a single TL074.  I treat them
as completely independent opamps with impunity.