Constructional Difficulty: Quite Hard. Large number of parts and calibration required.
An excellent sounding and popular VCO (voltage controlled oscillator) module. The design was originally inspired by the classic sound of the Mini's VCOs with the central core of the oscillator being somewhat similar. However, a great many things have been added and changed to make it more suitable for a modern modular system.
Four output waveforms are provided simultaneously; falling ramp sawtooth, triangle, pulse and sinewave. Output levels are 10V peak to peak, in common with most modular systems.
Apart from the usual fixed 1V/octave modulation input, a fully variable exponential input is available as well as a fully variable linear modulation input.
Slave synchronisation is easily obtained by inserting a falling sawtooth waveform into the SYNC input. This input is level sensitive to allow different strengths of synchronisation. A front panel pot is provided to control the depth of the effect.
The pulse waveform can be modulated in two ways. You can have either 'centred' or 'edge' modulation styles. The former will modulate both edges of the pulse output. The latter modulates only one edge. This can have a profound effect on audio rate PWM. The selection is implemented by a simple switch on the front panel.
The pulse output features a useful method of maintaining average output level. This means that fast sweeps of pulse width no longer produce any audible clicks as they do on other VCOs you may have used.
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 Oakley VCO in a natural finish 2U panel showing an issue 6 main board with issue 5 socket and pot boards. All pots are 16mm Alpha/Alps types
The main board size is 108mm (deep) x 144mm (high). As with all Oakley projects the PCBs are double sided with through plated holes, have tough solder mask both sides, and have bold component legending for ease of construction.
The VCO module features uses a three PCB set. Each PCB can be puchased individually. The three board method allows all the wiring to be done with a special socket PCB, special pot board PCB and 0.1" flexible connections. The VCO electronics are housed on the main board. The interconnection between the main board and pot board is via a 8-way preformed jumper interconnect. If you are building this module this system will reduce assembly time by at least an hour and a half!
Some people will wish to use this Oakley design in a non standard format, such as fitting it to another manufacturer's rack or one of their own invention. This is perfectly easy to do. Simply do not purchase the socket board or pot board and wire the main board to the sockets as per usual.
Sound Sample Downloads
Some MP3 samples of the Oakley VCO in action. The VCO was controlled by a midiDAC-2. Its output was fed into an Oakley ADSR/VCA and then onto the desk for recording. Only one VCO output is being heard, although for the sync'd samples, another VCO was required to provide the master frequency.
vco-sin.mp3 Sinewave output. Short sequence with light reverb. 85KB
vco-pwm.mp3 Pulse output. Same short sequence with EG sweeping the pulse width. 90KB
vco-pw.mp3 Pulse output, manually swept from 10% to 90%. Short sequence with light echo. 257KB
vco-sync.mp3 Sawtooth output. The VCO you are listening to is synchronised to a second VCO via its 'sync' input at a fixed frequency. The first VCO is now a slave VCO. The coarse frequency pot of this slave VCO is swept manually up and then down. 209KB
Click here for how to order.
VCO main board issue 6 PCB............................................... 19GBP
VCO socket board issue 5 PCB
VCO pot board issue 5 PCB ................................................... 3GBP
VCO pot bracket kit .................................................................. 1.25GBP
1K +3500ppm/K temp co resistor ........................................... 5GBP*
The VCO pot bracket kit contains five Alpha pot brackets. The brackets are used to hold the PCB mounted Alpha pots safely to the PCBs.
*1K +3500ppm/K parts are only available to purchasers of the PCBs. They are not available to buy separately.
All other parts can be purchased from your usual electronic component supplier.
All prices include VAT at UK rates. Shipping and postage is additional to these prices. Click here for full price list and ordering details.
Ready made VCO modules in both MOTM and MU formats are available from Krisp1.com.
VCO User Manual
Issue 6 VCO 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
Links to schematics are available to purchasers of the PCB or module 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 in traditional black
5U format in natural silver
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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