I had only one stereo filter in Eurorack, the Vult Freak. Freak is a versatile digital filter, but I wanted to get an analog stereo filter. Some searching brought me to the Patching Panda Moon Phase. I found a full kit at Modular Addict. This is a simple build on a single PC board with all the SMD parts pre-soldered.

After soldering just a few parts on the PCB all that remains is to insert all the panel parts, place the panel over them, secure and solder. There was one hitch. The two washers supplied for each pot were too thin to make everything line up properly, so I used some of my own washers over the pots.

I had enough spare Bananuts to decorate the panel. Gold for inputs, Black for outputs, Blue for CV inputs, and Silver for trigger inputs. The silver nut makes the MODE trigger jack stand out.

Why this stereo analog filter?

I was sold on it by watching the DivKid video linked on the manufacturer’s web page I linked above. He patched LFOs to all of the CV inputs and sort of went wild!

This is a somewhat unusual filter. It has eight combinations of Left + Right filter types, all 12db/octave slope:
LP + NOTCH,
BP + HP,
LP + BP,
BP + BP,
HP + HP,
LP + LP,
LP + HP,
NOTCH + BP

These types are selected by the middle button or by a trigger on the MODE input. Each button press/trigger advances to the next mode, which is indicated by a corresponding LED. The trigger input can be audio rate, as can any of the CV inputs. I found the audio rate modulation ability to be especially attractive, given that no DSP is involved.

The Controls

The typical filter controls are conjoined; Frequency, Frequency CV, and Resonance or Q affect both filters. But the Span control and CV spreads the center frequency of the two filters. The Span knob works as an inverting attenuator for any CV, but also spreads the frequencies with no CV patched.

The Stereo Imager is a unique feature that moves the sound around the stereo field. It has a non-attenuated CV input as well that can be audio rate modulated.