Oakley Modular Euro SVF (State Variable Filter)

The Oakley SVF is a 10HP wide two stage multimode filter module capable of high pass, low pass, band pass and notch output modes. All four outputs are available simultaneously. The module is a stand alone version of the filter in the Oakley ASV 5U module which 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.

The module has two audio inputs, each with its own mini level control, which are mixed together before being sent to the filter core. The mixer can be operated in either ‘clean’ or ‘soft clip’ modes. Clean mode will simply mix the signals together and feed them cleanly into the filter core. Soft clip mode will gently limit the maximum voltage output of the mixer rounding off the top and the bottom peaks of the audio signal. In soft clip mode the asymmetry control allows you to force the mixer’s output harder into the negative soft clipping zone distorting the audio in an interesting way.

The module requires +/-36mA at +/-12V.

The SVF module comprises of two printed circuit boards (PCBs) connected together with six 0.1 (2.54mm) single in line (SIL) headers and sockets. The main board on the rear of the module houses the power input and conditioning, the filter core, exponential convertor and output circuitry. The pot board has the pots, switch, and sockets that are attached to the front panel, as well as the mixer, soft clipping circuit, and
CV summing circuit. The main board is a four layer design, while the pot board is a two layer design. Each board is the same size;
49 mm x 107 mm.

The majority of the components are surface mount parts. The ICs are SOIC, and the resistors and surface mount capacitors are 0805.
The two transistors are SOT23, and the PNP matched pair is a SOT457. All components are standard parts.