Oakley DCR320 – Classic Stereo Chorus Module
Constructional Difficulty: This is
a large and complex project with a great many parts. An
oscilloscope is required for calibration.
A completed DCR320 fitted into a 1U high
250mm deep rack. The front panel and legending is a printed metal
overlay made by Schaeffer.
The Oakley DCR320 is a stereo ensemble unit designed
to mimic the behaviour of a well known stereo chorus rack effect
used in countless audio productions since the early 1980s. The
original unit, and its various clones, have only four preset
buttons on the front panel which limited the amount of control
the user had on the effected sound. The Oakley DCR320 has no such
buttons but instead allows full control over the most important
parameters.
The DCR320
now provides controls for the wet/dry mix, the amount of left
right cross processing, the modulation speed and depth, the
modulation waveform and phase, and the delay time.
Input and output
level control pots are also provided to allow maximum flexibility
in dealing with a variety of input signal levels. Both the stereo
input and output connections are balanced but can be used with
unbalanced connections if desired. A mono/stereo switch is
available on the front panel to allow just a single input to be
processed in stereo.
In the DCR320’s
classic mode the unit features the original tonal equalisation
and companding noise reduction circuitry which keeps unwanted
noise levels to an acceptable level while also adding a ‘vintage’
sound of its own.
In the DCR320’s
clean mode the unit now gives a sound more reminiscent of the
chorus units used in classic analogue synthesisers. The clean
mode has no companding circuitry, no noise shaping EQ, and the
effected signal has a wider bandwidth. Intermodulation distortion
is significantly less in this mode which means pad sounds remain
clear. However, the downside, like the original chorus units the
clean mode tries to emulate, is that the audio outputs have a low
level of swishing white noise that comes from using BBD devices.
A four LED level
meter helps you keep signal levels at optimum ensuring the best
signal to noise ratio without clipping.
Two
3207 BBDs run from +9V act as the delay elements.
The unit is designed to be built into a 1U high full width 19” rack
and uses no difficult to get parts. The unit can be powered from an external Yamaha PA-20
‘line lump’ type mains adapter, or, if you know how use high
voltages safely, an internal mains transformer.
An
optional input/output board has been designed to go with the DCR320
main board. This features space for four Switchcraft 114BPCX
sockets (or equivalents) and has a relay controlled muting
circuit to reduce thumps on the audio outputs when the power
supply is switched on and off.
The DCR320’s main board can be wired to its sockets
directly if desired but an optional I/O board is available which
makes wiring easier and also has a relay based anti thump circuit.
The
main DCR320 PCB is 280mm (width) x 153mm (depth) and is a four
layer design using only through hole components.
The
power to the unit should be a regulated split supply of +/-15V.
Power is admitted onto the main circuit board via a five way 0.156
(2.96mm) header of MTA or KK type. Power consumption is around +190mA
and -140mA at +/-15V. An optional power supply module has been
created for the DCR320 called the RPSU. This is designed to be
run from an external AC output mains adapter such as the widely
available Yamaha PA-20. However, an internal mains transformer
can be used with the RPSU if you have sufficient knowledge on how
to install one safely. The RPSU PCB is 150mm x 51mm.
The
RPSU designed to power the DCR320 main board circuitry with +/-15V.
This is a big and complex project with a large
number of parts there are over 190 resistors alone. Proper
calibration can only be done with an oscilloscope.
Sound Samples
This is a six part sample set of the Oakley
Sound Systems DCR320 stereo chorus. Each part starts with the
unprocessed sound.
In the first part you will hear a raw
sawtooth Dm chord being processed by the DCR320 to introduce
stereo vibrato at a variety of LFO speeds. The second part gives
an example of the clean chorus sound at a variety of LFO speeds.
The third part is of the DCR320 in classic mode with the balance
control central and the LFO speed slightly changed towards the
end of the sample.
The fourth part is a simple filtered
sawtooth sequence in clean mode to give a stereo chorus – the LFO
speed is varied througout the sample. The fifth part is the same
sequence this time in classic mode – again the LFO speed is
varied througout the sample. The final part is a different
sequence using two VCOs and with the DCR320 in clean mode.
The first prototype uses an internal mains
transformer. The case is a 250mm deep 1U high 19″ rack case.
Prices
DCR320 issue 1 PCB
……………………………………………. 36GBP
SREIO issue 2 PCB
………………………………………………… 8GBP
RPSU issue 2.1 PCB
…………………………………………….. 12GBP
DCR320 Pot Bracket Kit
…………………………………………. 1.75GBP
3-pin power socket for external PSU
………………………… 2.50GBP
The DCR320 pot bracket kit
contains seven special pot brackets. The brackets are used to
hold the PCB mounted Alpha or ALPS pots safely to the PCBs. They
are not required if you are using different types of pots or hand
wiring any pots to the board.
Most of the other parts should be able to
be purchased from you usual electronic component supplier. Please
see the Builder’s Guides for more details.
See the Oakley Sound ordering
page for ordering information, shipping charges and payment
methods.
All prices include VAT at UK rates.
Shipping/postage is additional to these prices. See also the FAQ page.
The three pin power socket for use with
external PA-20 power supplies.
Downloads
Construction
Guide Our handy guide to building
Oakley DIY projects
Parts
Guide Our handy guide to buying
parts for Oakley DIY projects.
DCR320.fpd Frontplatten Designer file of the suggested panel
overlay design. You can edit this to suit your own panel design
or print it out to use as a drilling template.
RPSU
shim.fpd Frontplatten Designer file
for the suggested heatsink shim plate.
Use ‘save as…’ button to
download and view the files.
The schematic is provided only
to purchasers of the printed circuit board. This will be sent to
you as a PDF file with your shipping confirmation e-mail.
To read the
Frontplatten Designer files you will need a copy of ‘Frontplatten
designer’ from Schaeffer. The program
also features on-line ordering. The company are based in Berlin
in Germany and will send out 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.
For technical support on all Oakley
projects please refer to the knowledgeable and helpful Oakley Sound Forum
which is hosted at ModWiggler.com. Tony
Allgood does not provide official building support for Oakley
projects, but he and many others are usually available for help
via the forum.
The 2 mm thick printed overlay is fixed to
the front of the rack case to provide a neat front panel.
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