Module A-121-3 is functionally nearly identical to module A-121-2. Only the distances between the controls and sockets are smaller and rubberized, small rotary knobs are used. Therefore the front panel width is only 4HP compared to 8HP of the A-121-2. In the first place it is planned for applications where only limited space is available. The only functional difference compared to the A-121-2 is the missing attenuator for the resonance CV input CQ.

These are the most important features of the module:

- Voltage-controlled multi-mode filter with a cut-off slope of -12 dB / octave (identical to the filter of the Dark Energy II / III but has been expanded by the voltage controlled resonance feature)
- Four simultaneous outputs are available, each with different characteristics: low-pass (LP), high-pass (HP), band-pass (BP) and notch (N)
- Manual control Frequ. for the cut-off frequency of the filter (the cut-off frequency determines the point at which the respective filter effect appears)
- Two inputs for frequency control by means of external control voltages (frequency modulation, e.g. by ADSR or LFO):
- Control voltage input CV1 without attenuator, about 1V / octave sensitivity
- Control voltage input CV2 with attenuator FCV2 for the adjustment of the modulation depth of input CV2
- Frequency range about 10Hz ... 20kHz
- Manual control Q for the resonance of the filter
- Control voltage input CQ without attenuator for voltage control of the resonance
- Resonance up to self-oscillation, in which case the module will behave like a sine wave oscillator even without audio input signal
- Audio input In with attenuator Level for the adjustment of the filter input level (beyond about pos. 5 clipping / distortion occurs with typical A-100 audio levels)