[sdiy] Cheapest, simplest but still reliable VCO & VCA for polyphonic project

[Andre Majorel]

On 2009-01-09 03:49 +0000, Karl Ekdahl wrote:

> I thought about the simple resistor-transistor idea that JH
> talked about but i couldn't find any good references to this
> (and i'm gonna guess it's a little tricky seeing we're talking
> DC here)..

Single-transistor VCA :

- Q19 in the MS-20 (in [1], "C945 SELECTED" just left of the
  bottom right op amp).

- Q401-Q412 in the PS-3200 (in [2] both below pin 8 of KORG35, in
  [3] around "2SC945 (SEL)" on the right).

Single-diode VCA :

- D401-D412 in the PS-3200 (in [2], both below pin 8 of KORG35, in
  [3], around the diode near the "PK" label)

They're all AC-coupled. Wonder what would happen if you used that
circuit DC-coupled...

[1] http://www.korganalogue.net/korgms/images/service/ms20/circ2.gif
[2] http://www.jhaible.heim.at/polykorg/PS3200_Voice_Cards_orig.gif
[3] http://www.jhaible.heim.at/polykorg/jh_3200_gates_2of2.gif

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>