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 new issue 4 VCO PCB set in the 2U panel showing all three PCBs and their interconnections. All pots are now high quality Spectrol 248 types
The Issue 4 PCB set
The VCO module features a three PCB set. Previously, older Oakley modules have had the sockets, switches and extra pots wired to the board by individual wires. The new method allows all the socket wiring to be done with a special socket PCB and MTA solderless connections. The electronics are housed on a main board and an auxillary board. The interconnection between the two boards is via a 8-way preformed jumper interconnect. If you are building this module in the standard MOTM and Oakley format this new 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
Issue 4 User Guide for the current issue VCO module
Use 'save as...' button to download and view the file. IE users need to right hand mouse click and then choose 'save as'. Links to protected schematics are available to purchasers of the PCB or module and will be sent via e-mail when the board(s) are shipped.
Parts lists for US builders
Builders based in North America can now find full parts lists, complete with order codes, for many of the Oakley modules. Larry Hendry kindly provided the web space for customers to upload parts lists. Go to www.wiseguysynth.com for full details.
Front Panel database
A Schaeffer front panel can be made for the VCO module. The databases can be found here:
Issue 1 & 2 panel or Issue 3 & 4 panel
Earlier issues can use either database, but issue 3 and 4 boards will only fit in the Issue 3 & 4 panel design. 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 PCB set of three boards............................
25GBP
1K +3500ppm/K temp co resistor
.................................... 5GBP
VCO pot kit
........................................................................
21GBP
VCO pot bracket kit
............................................................ 7GBP
The VCO pot kit now contains seven Spectrol 248 pots sufficient to make up one 2U wide panel. No knobs or switches are provided. The VCO pot bracket kit contains seven Oakley pot brackets and seven extra pot nuts. The brackets are especially made for us to hold the PCB mounted Spectrol pots safely to the PCBs and cannot be purchased anywhere else.
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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