Marsupial is a Dual AS3350 Voltage-Controlled Filter from SetonixSynth. I don’t use filters often in Eurorack, but I built this one for my Noise Rack (next post). I like the functional design of Marsupial and it sounds great too.

Marsupial User Manual

Audio goes into the Marsupial via the two jacks labeled “A-Audio In-B”. If audio is patched to the A input, it will be normalized to the B input. Each audio input is routed to a discrete single-supply JFET buffer pre-filter. The buffers will introduce a subtle saturation/clipping sound to the audio inputs once the signal level reaches approx. 8Vp-p, providing some nice added harmonic material for the filters when driven. If a clean sound is desired, simply turn the input level down using a passive attenuator; a higher Resonance setting will reduce the filter’s amplitude somewhat as well.

The outputs of each buffer are routed to the Marsupial’s two separate filters, referred to on the panel as “A” and “B”. Each Filter has an Control Voltage input with attenuverter, unattenuated 1V/Oct control input, and Bandpass and Lowpass outputs. The Global Cutoff and Resonance knobs provide master control over the cutoff and resonance of both filters respectively, while the B Offset knob positions Filter B’s cutoff relative to that of Filter A, providing an offset of approximately 2.5 Octaves on either side of center. The LEDs labeled “A” and B” are purely cosmetic and indicate substantial audio output from the Lowpass output of the corresponding filter.

Arrows on the panel between each input indicate normalization from Filter A to Filter B, with any signal inserted into a Filter A input automatically being routed to the corresponding input on Filter B unless the normalization is broken by the insertion of a separate Audio or Control Voltage signal for Filter B.

As an added performance feature, the Series/Parallel switch changes the input of Filter B between its Audio Input jack and the output of Filter A. The Filter A output routed to the Series/Parallel switch is selected via the rear 3-pin header. For maximum available bandwidth, we recommend using the Lowpass output.

The Kit and Build

I bought a full kit from Modular Addict. I could have sourced the parts, but decided to save myself the trouble. This is another very easy kit to build, the PC board already having all SMD parts installed. You just solder the trim pots, power header and one jumper header on the back, and then all the panel parts on the front.

If I had had a pair of B100K 9mm Alpha pots on hand, I would have tried substituting them for the trimmer type pots used for the CV attenuators. I still might swap them in the future, because the plastic pot shafts are flimsy and I put Dark Red Davies 1900 clone knobs on them.

The trim pots on the back are for 1V/octave calibration.

I keep a supply of 10-pin keyed headers on hand to swap in — if there’s room — when a kit comes with an unshrouded header. It worked for Marsupial, even though the header shroud sits on top of some SMD components.