[sdiy] Buchla 257 is an extremely strange circuit
derek at umatic.nl
Wed Dec 16 08:50:20 CET 2009
my apologies of this thread is dead and buried, but I'm interested in
analog computer functions and ways of "interpolating" or cross-fading
between them, or between the input signal and the processed signal. This
PWM AM sounds rather complicated to implement, would there be a simpler
VCA-based solution? Something like the Serge sound processing module
with it's voltage controlled cross fader? or am I missing something
important in the concept of a CV crossfader/interpolator?
Aaron Lanterman wrote:
> I know using "Buchla" and "extremely strange" in the same sentence isn't
> exactly news, but this is even stranger than usual.
> The 257 is the Dual Control Voltage Processor. It has a means of
> crossfading between two CVs by means of a third signal.
> The way it does this is totally odd. There's a fixed frequency triangle
> wave oscillator running at 21 kc, and then the controlling CV is added
> to that. This is then run through a comparitor, so you get a pulse wave
> whose duty cycle is determined by the CV.
> This pulse wave then controls some CMOS switches, set such that you get
> a signal that is CV1 part of the time, and CV2 part of the time,
> depending on that pulse wave. So depending on the duty cycle, it spends
> a particular amount of time at CV1 vs. CV2.
> Then, this goes through a boatload of lowpass filtering to smooth out
> things and average the signal.
::: derek holzer ::: http://blog.myspace.com/macumbista :::
---Oblique Strategy # 36:
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