Oakley Sound Euro Rack Classic VCA User Manual
Oakley Sound Systems
Euro Rack Series
Classic VCA
Discrete Core Voltage Controlled Amplifier
User Manual
V2.2
Tony Allgood
Oakley Sound Systems
CARLISLE
United Kingdom
Introduction
This is the User Manual for the Classic VCA 3U module from Oakley Sound. This document
contains an overview of the operation of the unit and the calibration procedure
For the Builder's Guide, which contains a basic introduction to the board, a full parts list for
the components needed to populate the board or boards, and a list of the various
interconnections, please visit the main project webpage at:
http://www.oakleysound.com/vinvca.htm
For general information regarding where to get parts and suggested part numbers please see
our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf.
For general information on how to build our modules, including circuit board population,
mounting front panel components and making up board interconnects please see our generic
Construction Guide at the project webpage or http://www.oakleysound.com/construct.pdf.
The prototype Classic VCA module using a 10HP wide Scheaffer panel. Note that on this module the
sockets are on the right of the pots. The Krisp1 manufactured version has the pots to the left and fitted
with an 8HP wide panel. The functionality is the same however.
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The Oakley Classic VCA
This is a vintage voltage controlled amplifier design. It is based on the classic ARP4019 submodule which was used on the wooden case ARP2600P semi-modular synthesiser. The design
has a fully discrete core but uses a single high quality audio op-amp for output amplification.
The unit features both linear and exponential control voltage (CV) inputs. Both can be used
together or individually.
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 provides a DC block
to process only alternating frequencies. Both inputs can be used simultaneously and each one
features an input level control.
A gain control is also available to provide a fixed bias to set the initial gain of the VCA. This
way a negatively going CV can reduce the overall gain of the VCA. The gain pot can also be
used a volume control.
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