Elby Designs CGS364 VCA Instructions for use

CGS364 VCA
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
[email protected] http://www.elby-designs.com
1 of 3
CGS364 VCA
Construction Guide
Revision 0.0
March 30th, 2019

CGS364 VCA
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
[email protected] http://www.elby-designs.com
2 of 3
3D Model
Schematics
Constructors should refer to the printed Component Overlay along with the PCB
Bill of Materials for the current value of all components and General Construction
Notes for general PCB assembly guidelines.
The SIGNAL inputs are, by default, AC coupled and so are only suited to audio
type signals. If you wish to control CV type signals then replace the relevant input
capacitors (C3, C4 and/or C5) with a wire link.
The CGS364 requires a matched NPN transistor pair in the Amplifier Stage at Q5
for optimum performance. Please refer to Dual-Matched Transistors for further
details.
Calibration
P3 [OFFSET] is used to set the DC offset of the output to zero. P2 [CV REJECT]
is used to null out the effect of the control voltage on the output.
If fitted, set P4 [INITIAL GAIN] to 0V (fully CCW).
Connect a varying waveform of low frequency (triangle wave from an LFO is ideal)
into the [CV 1] input of the VCA, and turn the associated level pot to maximum.
Connect the output of the VCA to a control voltage input of a VCO. Monitor the
output of the VCO. You should now be able to adjust these trimmers so that there
is no modulation present on the output, and the output is at zero volts. Note that
these trimmers interact to some extent, so you will need to alternately adjust
them until the best result is obtained.
P1 [CV INIT] is used to set the VCA to zero gain at 0 volts CV input. Feed an
audio signal into the [CV 1] input, and monitor the output. With no CV at any of the inputs, and the optional
external [INITIAL GAIN] pot, if used, set to its zero position, adjust this until no signal is heard.
Wiring Guide – click for larger image

CGS364 VCA
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
[email protected] http://www.elby-designs.com
3 of 3
CGS364 VCA – BoCGS BOG & MARSH
Constructors should refer to the printed Component Overlay along with the
PCB Bill of Materials for the current value of all components and General
Construction Notes for general PCB assembly guidelines.
Some resistors and capacitors associated with the CV and SIGNAL inputs are
not required in the BoCGS BOG and MARSH builds and may be omitted from
the PCB if desired (image below shows these components removed).
The SIGNAL inputs are, by default, AC coupled and so are only suited to audio
type signals. If you wish to control CV type signals then replace C4 with a wire
link.
The CGS364 requires a matched NPN transistor pair in the Amplifier Stage at
Q5 for optimum performance. Please refer to Dual-Matched Transistors for
further details.
BoCGS wiring (1 of 2 circuits) – click for larger image
Panel Bill of Materials