[sdiy] Vactrols & Lopass Gates

[Peter Grenader]

I've built all three types, many times over.  IMHO, the 292B sound best.
The external FET is warmer than just relying on the TLO internals.

As far parts subs, if you make the B, stick with the 2n4339.  I've tried
others and ... not so good.  The op amps can all go TLO or OPA if you've got
the means.  I've also found a way to kill the bleed associated with signals
hotter than Buchla (line) level inputs going thorugh LPGs, but if I told you
what that was I'd have to neuralize you as it's used in my Model 13.

stick with polystyrene's for the filter caps (.0047 and 220 pf) and cheap
disks for the .47's.  They sound better.

As far as the analog switch, i've never done that.  Why? If you're making a
rev C, using a triple pole switch will do the same thing and it's less - see
my LPG schemo on my site.  For the rev 2, a double pole.  No fuss, no muss.
Remember, the main reason for the analog switch in the original was to
introduce computer signals via the 300 mainframe.

if you don't have a 3/2 vac, two VTL5C2's in series will work and it adds a
bit of that 'oh SO swee't ring as both vacs will add their own ring. My
favorite LPG has two 2's in series.

hope this helps.

- P



Michael Ruberto wrote:

> Alright I submit, I will include some lopass gates in my new synth. 1st I
> have some questions. There are a handful of different schematics floating
> around on the web, which is the best to use as my example?
> I have the original schematic drawn by buchla but it gives me a headache to
> look at. I see from the datasheets that the Vactrols all have different
> rise/fall times ranging from 2.5 to 4+ mSec. Does anybody know which were
> used on the original? Does it matter?
> 
> I plan to use an analog switch and have some samples of the ADG333.
> http://www.analog.com/en/prod/0%2C2877%2CADG333A%2C00.html
> Will these work alright?
> 
> Finally, any comments, advice, recommendations, on parts and construction
> much appreciated.
> 
> Thanks
> M. A. Ruberto
> 
> PS: Anybody have the PCB footprint for the Vactrols?
> 
>