[sdiy] Multiplier vs VCA

[Derek Holzer]

Howdy there SDIYers,

my next design question for my new project deals with amplitude 
modulation. I will construct a module inspired by the Buchla 259 
Programmable Complex Waveform Generator, as well as the Cwejman VCO-2RM, 
in that it will contain two oscillators (2 x Thomas Henry XR VCOs, using 
the Bugbrand PCB layout) with a number of switchable modulation 
possibilities (PWM, AM, FM...).

I had originally intended to use a full-fledged VCA for the AM function, 
but then I ran across Timothy Daugard's implementation of the diode 
quadrant multiplier which says it is capable of "VCA type effects" when 
the inputs are DC coupled:

http://members.cox.net/synthfred/h_kmd101.htm

So my question is: what would I gain by building a (more complex) VCA 
for the AM section of this design, over using this simpler diode 
quadrant modulator? The VCO-2RM uses a ring mod (most likely a 
multiplier), as the name implies, and I'm not at all sure what the 
Buchla 259 uses. Keep in mind that the module will not be set up to take 
an envelope or any other signal for the AM, as I would use another VCA 
module for any other AM needs later on.

Best!
Derek

-- 
::: derek holzer ::: http://blog.myspace.com/macumbista ::: 
http://www.vimeo.com/macumbista :::
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