[sdiy] best soundign vco design?

[Roy J. Tellason]

On Saturday 12 June 2004 07:26 am, Dana Scott wrote:
> I have seen at least one site on the 'net with schematics of the potted
> modules posted.
> Early potted modules were completely encased in epoxy. By the time I
> started working at ARP (Feb. 1974) they were potting them in soft RTV
> rubber with a thin layer of epoxy on top. These were frequently cracked
> open and repaired.  The Avatar E' module was an exception. All of those
> were hard potted... Well, not _all_ of them. I have one that is not potted.
> Somewhere in my files I have a 1:1 film negative for a 4027-1 VCO.  I don't
> think board houses will accept films without NC drill info anymore. On one
> of my old computers I have a CAD board layout I did of one of the modules,
> ring mod I think.
> I was thinking of running off a batch of 4109 filter modules. The 4109 is
> the filter used in the Centaur prototype. It is a VC state variable filter
> with low pass , high pass, bandpass and notch outputs, It uses the same
> basic filter section as the 4075 and 4072 filters and has voltage
> controlled resonance too. Do you think it would be work my effort to
> produce a batch of these?

I have *no* idea whether it would or not,  since I've been out of this stuff 
for a number of years and am only just recently starting to dabble in it 
again.

FWIW,  in all of the repairs I did I ran across *one* module that was not 
potted.  My recollection of this is pretty vague,  but I think it might have 
been an oscillator module in a 2600 or an Odyssey.  Maybe a filter,  I dunno.

And then there's that "keyboard op amp" that the 2600 used.  I actually 
managed to *make* a couple of those,  for a couple of different people,  
using a circuit that had a regular op amp and one of those dual FETs that a 
number of different instruments used.    :-)

> -Dana

Any chance that we've met?

> ----- Original Message ----- >
>
> > Any of you guys know if the details of those potted modules that ARP used
> > to use ever got out?  Just curious,  mostly...
> >
> > Wanna talk about "fat" sound?  Best I ever did was to have _THREE_ 2600s
> > finished up at one time and still on the bench.  So of course I patched
> > 'em together... :-D