[sdiy] Updating the Tau 1010 VCO

[David G. Dixon]

> I sent her the note below; please let me know if I said 
> anything that's off-base and might lead her astray...

> I have no idea what the original transistors were; you should 
> be able to use 3906 and 3904s where appropriate for Q4, Q5, 
> and Q6.  For the JFET - I guess it's labled Q3? - try a J201 
> or MPF102 (if the stock room doesn't carry those let me know).

I think this JFET should have a pretty low on-resistance.  A rapid switcher
like 4391 might be better.  I've also used 5485 in similar applications, and
3819 might be good as well.  I haven't had much luck with J201s in any
application I've tried them in, I'm afraid.

> For right now, you can grab a random capacitor to play the 
> role of the integrating cap hanging off of the 3080, but at 
> some point want to swap this out for a higher quality 
> polysterine or polypropeline cap.

I use monolithic C0G ceramics for VCOs (should I duck?).  Your EE stores
should probably stock those in 390pF.  Ian Fritz has weighed in on this
debate before, and there are other web resources to suggest that, in all the
places where it counts, the C0G monolithics perform at least as well as the
polys.