Dual and Quad Voltage Controlled Amplifier and Mixer
The suggested front panel for the double
width Oakley Quad VCA with 20mm control knobs.
This voltage controlled amplifier (VCA)
module can be built either as a single width two channel VCA or a
double width four channel VCA. Each VCA stage is identical and
each features a high quality analogue VCA based around the 2164
chip with very low noise and very low CV breakthrough.
If the output socket of any VCA channel is
unused then that signal will be mixed with the output of the
final channel. That is, in the four channel version this module
can be used as a four channel voltage controlled mixer. However,
any VCA channel can simply be taken out of the mixing process by
inserting a jack lead into its respective output socket.
Each VCA has two controls. Firstly, there
is GAIN, a fixed bias to set the initial gain of the VCA, it can
also be used a volume control. Secondly, the CV pot allows you to
alter the sensitivity of the external CV that controls the VCA’s
gain. The pot is a ‘reversible attenuator, so you are able to
control not only the depth of the modulation but also the
polarity. With the CV pot set straight up no CV signal reaches
the VCA. With it fully right the CV is applied so that positive
CVs increase the gain of the VCA. With the pot fully left then
increasing positive CVs reduce the gain of the VCA. A single D-VCA
module can used to crossfade between two signals, or pan one
signal to either the left or right audio output.
Each VCA can be set with its front panel
switch to respond either as a standard linear VCA, an exponential
VCA, or with the switch in the middle position, as a mixture of
the two responses. Each VCA is direct coupled and can therefore
process CVs and audio signals.
The spacing between the pots is our smaller
standard of 1.375″ (34.9mm). Used in conjunction with
smaller 20mm (13/16″) diameter knobs this still allows for
an attractive module design and finger friendly tweaking.
The suggested front panel for the single
width Oakley Dual VCA with 20mm control knobs.
Power (+/-15V) is provided to the board
either by our standard Oakley 4-way header or Synthesizers.com
header. Current consumption is approximately 35 mA per rail.
The PCB is 85 mm (deep) x 124 mm (height).
The four pots are normally board mounted for speed and simplicity.
The main PCB is a four layer design with through plated holes,
tough solder mask both sides, and bold component legending for
ease of construction.
The Oakley Dual VCA built with the issue
Dual VCA-X board as a single width MOTM format module in a
natural finish Schaeffer panel. Note also the use of the optional
Sock6 socket board to help keep the wiring to the sockets neat
and tidy . The unfitted 2 x 5 IDC header at the bottom of the
board is the BUS connector that joins this module to another Dual
VCA board to create the Quad VCA.
Project Downloads
Construction
Guide Our handy guide to building
Oakley DIY projects
Parts
Guide Our handy guide to buying
parts for Oakley DIY projects.
Schematics are only available
to purchasers of the PCB(s) and will only be sent via e-mail when
the board(s) are shipped.
Front Panel database
A Schaeffer front panel can be made for
this module. The databases can be found by downloading the
following links:
5U format 1U
wide Dual VCA module in traditional black
5U format 2U
wide Quad VCA module in traditional black
5U format 1U
wide Dual VCA module in natural finish
To read, edit and print these
files you will need a copy of ‘Frontplatten Designer’ from Schaeffer. Panels can be ordered via the program using its
secure online ordering system.
Schaeffer are based in Berlin, Germany and
can send panels to anywhere in the world. Delivery to the UK
normally takes around ten days. For North American users you can
also order your Schaeffer panels from Front
Panel Express.
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