Voltage Controlled State Variable Filter

PCBs for this project have been discontinued.

The SVF in our 1U 'filter core' format.

This is a two pole multimode filter capable of high pass, low pass, band pass and notch output modes. All four outputs are available simultaneously. This new version of the very popular Oakley design is based around the classic two pole state variable filter topology as used in a variety of vintage synths including the Oberheim SEM and OB-X. At high resonance the Oakley SVF will oscillate over the whole of the audio band and is temperature compensated.

The design is intended to fit into a 1U wide 'filter-core' module or a more fully featured 2U wide panel with seven control pots.

The 1U 'Filter Core' format is our way of handling filter modules. Although the 1U module can be used as a filter module on its own, it is expected that users will make use of external mixers to control CV and audio levels going into the filter. In this way, you will be able to have a collection of space saving 1U filter cores that can be used with any generic mixer module. The Oakley Multimix is an ideal choice for a handy mixer module.

The SVF in the suggested full 2U format.

For the 2U design three audio inputs are provided each with its own attenuator. Three CVs can control the cut-off of the filter. One is fixed at 1V/octave, the other two have input attenuators. CV1 features a reversible type attenuator with inverting/non-inverting properties.

For DIY builders of this module it is possible to purchase the Sock8 circuit board which is available separately. This little board speeds up the wiring of the eight 1/4" sockets and reduces the chances of any wiring errors.

Power (+/-15V) is provided to the board either by our standard Oakley 4-way header or Synthesizers.com header. Current consumption is approximately 30mA per rail.

The issue 5.2 board size is 104 mm (high) x 99mm (deep).

The 1U version behind a natural finish Scheaffer panel. Note the use of the optional Sock-8 board to make wiring the socket field much easier.

Sound Samples

All the following samples recorded with a small set up comprising of two sawtooth VCOs, one SVF filter, two ADSR/VCA and a midiDAC to control them all. All the sounds were recorded without any effects added.

Using the low pass output. Two simple one note hits with the SVF set to medium to high resonance.

Using the band pass output. Two more simple one note hits with the SVF set to medium to high resonance.

Using the -12dB/octave low pass output. Simple 16th note sequence with an input from the sawtooth output of a single Oakley VCO. The filter is manually being swept via the 'freq', 'resonance' pots and altering ADSR sweep depth.

Using the notch output to give a phaser type effect. The SVF is driven from a triangle wave output from a VCO, first fast, then slow and then fast again.

This one may make you jump - watch your volume levels. This sample is using the low pass output and with the SVF set to full resonance to give self oscillation. The SVF is modulated by a swept sawtooth VCO and an ADSR.

Project Downloads

User Manual

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 filter core module in traditional black

5U format filter core module in natural silver

5U format full width module 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.

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Copyright: Tony Allgood.
Last revised: May 23, 2023.