New Wiard Module: Borg "Assimilator" Filters

[jhaible]

Hi Grant,

thanks for sharing this.

Yes, there was at least one Korg "Traveler" that was a Vactrol-based
Sallen & Key filter (actually two in series, one HP and one LP): The
Polyphonic Ensemble PE-1000. Only two transistors for amplification,
plus a 3rd one which only acted as a switch for Resonance on/off.

Building this, and building the Buchla lowpass gate, have been on my
to-do list for a long time. Stange that I never saw the connection between
them !

> The Vactrols also have slew rate limited control voltage
> response that gives everything a very acoustic tone
> character and that HUGE Buchla 200 sound.

[...]

> I have also built VCOs and VCAs with them,
> but the VCOs don't calibrate too well and the
> VCAs are "soft" sounding. But the filters are bitchin.

This is the part I'm most curious about. I thought the Buchla
was primarily a VCA, with the option to make the sound
darker as well as more attenuated at the same time, the VCF
function being just a resonance-less additional mode.
Now your results hint in another direction: Fast enough for
VCF but not for a general purpose VCA - did I get this right ?
Which Vactrols have you used (if I may ask), and did you
include Buchla's dynamic CV circuit (which supposedly
speeds up the Vactrol response by "enhancing the edges"
of the LED current) ? I always wondered how well that
part worked. I assume it can only speed up the response
of the LDR to a very small degree, but Buchla did his best
to squeeze the last bit of speed out of them. Does this
make sense, or did I interpret it wrong ?

> It has become apparent to
> me that fewer parts = less noise and I have been concentrating
> on designs that have the fewest possible number of parts in
> the audio path.

I like this !

Regards,

JH.