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Grove Audio has announced the GMS-294a VC Low Pass Filter – a faithful recreation of the classic Moog 904a 4 Pole Transistor Ladder filter.

The filter incorporates the same audio path and transistors used in the original filter, designed by Robert Moog. The GMS-294a adds an attenuator on the audio input and an attenuated CV input as well as a 1 Volt/Octave frequency control input.

The manual resonance control causes a peak in the low pass response and if increased to near maximum will cause the filter to go into sine wave oscillation.

The GMS-294a VC Low Pass Filter

The 1 MU wide module is available either assembled or in kit form, as shown here.

The kit comes complete with all the parts and with the potentiometer and jack leads pre-assembled. Even the solder is included. All the builder needs to assemble this kit is a narrow-tip soldering iron, long nose pliers, diagonal cutters, a small flat blade screwdriver to secure the knobs and a small or medium Phillips screwdriver. A wrench for tightening the pot and jack nuts is also recommended.

This kit includes complete instructions for assembly and is recommended for builders with intermediate kit building skills. Some calibration is required after assembly and minimally requires a voltmeter although a waveform display of some kind is helpful.

Pricing and availability for the Moog filter is TBA.