Journeyman

Diode Ring Filter

This is a 6HP wide four pole dual mode filter module capable of either -12dB/octave low pass or -6dB/octave high pass responses.

The Journeyman's nonlinear signal behaviour and discrete circuitry gives it a unique sound of its own. Partially modelled after the classic Japanese Traveller filter design from the mid to late 1970s, the Journeyman can be configured in either -6dB/octave high pass or -12dB/octave low pass modes by a switch on the front panel. When two of these VCFs are used in series, one in HP and the other in LP, then the effect is astounding.

The filter core is made entirely from a single ended discrete design and uses a ring of four diodes (actually the base-emitter junctions of four high quality matched NPN transistors) as the control elements. The filter behaves very differently depending on the input signal level hence the usefulness of a 'drive' pot on the front panel. Turning this up allows the filter to be overdriven, without changing the output volume, and dramatically changes the sound at higher resonance settings. At high resonance the filter will self oscillate across most of the audio band.

Two control voltage (CV) inputs are available on the front panel. CV1 offers the standard 1V/octave control over the cut-off frequency. While CV2 has a depth control which can be varied from off to up to 0.5V/octave, and has additional switch that can invert CV2 if negatively going sweeps are desired.

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