Quantity: 2 Tube VCA’s in one panel

Ken Stone’s CGS 65 Tube VCA:

This is a tube based Voltage Controlled Amplifier / timbral gate. While this module basically operates as a VCA, it does add a degree of distortion to the signal. How much distortion depends on how hard it is driven. Add feedback and it begins to oscillate, synchronizing to the incoming signal to some extent. All this while running on a standard synthesizer power supply, with no extra heater supply required.

Modifications:
Custom Front Panel Express panel
Changed output gain resistor to 49K to add oomph.

Each module has two audio inputs with attenuator pots. The second input is normally connected to the output of the VCA for feedback. This module produces a warm “tube” distortion, because it actually uses a tube! Shielded cabling is used for all audio paths.

The mounting brackets are from:
Scott Deyo
The Bridechamber

DEMOS

These two demos use both the CGS-65 and the MOTM-190 VCA. We hear a sine wave from a MOTM-300 VCO. Both VCA’s are controlled by the same envelope generator. The first demo starts out with 30 seconds of MOTM-190. It fades to the CGS-65 with the input at a low level (IN 1 knob at 1.5), yielding hardly any distortion. As the IN 1 knob is gradually turned up to about 7, the distortion increases. Then IN 2 is turned up, adding feedback, and the distortion goes wild. After about 5 on the dial subharmonics start kicking in. As the envelope sweeps there there is a really nice effect as the subharmonics ring. Then the MOTM-190 is mixed back in, layering the fundamental, which resonates with the harmonics. Finally the CGS-65 is faded out, leaving only the 190 again at the end.

Podcast (audio2): Play in new window | Download

Podcast: Play in new window | Download

Now double it all by adding a second MOTM-300, CGS-65 and MOTM-190. There’s still only one envelope generator driving it all. Pitches are courtesy of the CGS Infinite Melody quantized by two Blacet Miniwaves.