The suggested front panel design for the
Classic VCA
This is a
voltage controlled amplifier module inspired in part by a classic
vintage design. The Oakley Classic VCA is based on the ARP4019
sub-module which was used on the wooden case ARP2600P semi-modular
synthesiser. The design has a fully discrete core but uses op-amps
for input summing and the output drivers.
Two signal
inputs are provided, one DC coupled and the other AC coupled. The
former allows audio and low frequency signals to be processed.
While the latter has a high pass filter so that it can be only
used to process alternating frequencies. Both inputs can be used
simultaneously and each one features an input level control.
Two control
voltage (CV) inputs are provided. CV1 is linear and is provided
with a standard attenuator pot that can control the sensitivity
of the input. CV2 can be operated in either exponential or linear
mode.
CV2 features a
reversible attenuator. When the pot is turned right of its
central position, the pot acts as a normal attenuator; increasing
the sensitivity of the CV input. Left of centre, the pot will act
in inverting mode and the CV will be tipped upside down so that
increasing positive voltages will decrease the gain of the VCA.
When no input
jack is inserted into the CV1 input, the CV1 pot becomes a gain
control. This allows the pot to be used as a simple volume
control but when set high it also allows CV2 to turn the VCA off.
The 5U version
of the Classic VCA has two outputs. OUT A is the standard output
of the VCA. OUT B, gives you the difference signal between the
sum of the two inputs and the final output of the VCA. This is a
sort of anti-output; when the VCA output signal goes up in level
this output goes lower. You can use it as a ring modulator (with
gain pot set to max) or in conjunction with OUT A as a voltage
controlled pan.
Power (+/-15V) is provided to the board
either by our standard Oakley 4-way header or Synthesizers.com
header. Current consumption is approximately 35mA per rail.
The main PCB is 89mm (deep) x 126mm
(height). As with all Oakley projects both PCBs are double sided
with through plated holes, have tough solder mask both sides, and
have bold component legending for ease of construction.
The prototype Classic VCA module using a
natural finish Scheaffer panel. Note the use of the optional Sock6
socket board to help keep the wiring to the sockets neat and tidy
.
Project Downloads
5U
Classic VCA Builder’s Guide
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 and will 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
Classic VCA module in traditional black
5U format 1U wide
Classic 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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