Wiardgroup

It's a mode unique to photo-electric filters. Any other transconductor (transistor, diode, 
OTA) can not run to zero control current without making bad things happen to the DC bias 
and producing 15 volt thumps.

But photo-electric filters go completely off (0 Hz). This allows you to use the filter as a 
combined VCF and VCA.

In the West Coast model, the complex timbres are generated before the filter via complex 
oscillators, non-linear waveshapers, FM or additive synthesis. The "gate" is then used for 
final amplitude and spectral shaping.

The Boogie supports both modes, either straight subtractive with a following VCA, like the 
East Coast instruments, or gating and spectral shaping without a following VCA, like the 
West Coast instruments.

The main frequency control covers 20 octaves, 0 to 20 Hz, which is 10 octaves, and 20 Hz 
to 20 kHz, which is another 10 octaves.

To "gate" with the Boogie, set initial frequency to zero and control range to max. 
Resonance is set to zero. A 10 volt signal into "Control In" will then sweep the filter from 0 
Hz to 20 kHz. The 6 dB output is approx. equivalent to the Buchla 292 "combo" mode, and 
the 12 dB output is approx. equivalent to the 292 "filter" mode. But the Hamamatsu opto-
couplers decay in 20 ms., rather than the 200 ms. decay of the VTL5C3/2 used in the 
Buchla 292C.

--- In wiardgroup@yahoogroups.com, "mrboningen" <darkflametwentythree@h...> wrote:
> Sorry if it's obvious, but could someone tell me exactly what a low
> pass gate is, and how I can use my Boogie filter as such?
> 
> Gregg.