Constructional Difficulty: Quite Hard. Large number of parts and calibration required.
An excellent voltage controlled oscillator (VCO), and now improved, for modulars and fixed architecture synths. But don't take my word for it...
"This VCO rocks!" A very satisfied customer
"The VCO is an excellent design" Another satisfied customer
This design was originally inspired by classic sound of the Mini's VCOs.The basic core of the oscillator is very similar, but many other things have been improved upon. For example, the exponential convertor uses modern day parts and the temperature compensation is provided by a high quality +3500ppm/K resistor.
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 inputs, 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.
The latest version of the module accomodates either our standard Oakley/MOTM power header or a Synthesizers.com power header.
The issue 5 VCO PCB set in a natural finish 2U panel showing all three PCBs and their interconnections. All pots are now 16mm Alpha/Alps types
The Issue 5 PCB set
The VCO module features a three PCB set. Early issue Oakley VCO modules have had the sockets, switches and extra pots wired to the board by individual wires. This method allows all the socket wiring to be done with a special socket PCB and 0.1" flexible connections. The electronics are housed on the main board and an auxillary pot board. The interconnection between these two boards 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 use the socket 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
Project Downloads
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
To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier to buy your panels from Scheaffer.
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.
Prices
VCO Issue 4 ready made 2U
module............................. 210GBP
VCO Issue 3 ready made 2U module............................. 185GBP
VCO Issue 5 PCB set of three boards............................
25GBP
VCO pot kit
.........................................................................
7GBP
VCO pot bracket kit
........................................................... 1GBP
1K +3500ppm/K temp co resistor
.................................... 5GBP
THAT300P quad NPN transistor array ............................ 6GBP
Issue 3 and 4 ready made VCO modules are still available for a limited period. The main differences between the modules are mechanical, but for a full account of the changes made between issue 3, 4 and 5 modules please see the User Manual.
The VCO pot kit now contains seven 16mm Alpha pots sufficient to make up one 2U wide panel. No knobs or switches are provided. 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.
All other parts can be purchased from you usual electronic component supplier.
See the prices 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.
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