A-105-1 SSM 24dB Low Pass Filter

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The module is no longer in production.

The A-105 (or A-105-1, there is now the polyphonic A-105-4) is also reminiscent of famous models. An analog SSM2044 filter circuit is used here, which was already used in synthesizers such as the Korg Mono / Poly, the Fairlight II, PPG Wave 2.2 / 2.3 and last but not least in the first – and by many the most highly valued – Prophet 5 synthesizers . Then it can’t be really bad…

The A-105 module also has a “design brother” (with a completely different sound, of course): the A-122 module.

If a single A-105 seems a bit puny to you, you can reach for the quadruple A-105-4 (which can be used in a polyphonic context).

User interface

Inputs:

  1. Audio In: Audio input.
  2. FCV1: Control voltage input for the cutoff-frequency (without attenuator).
  3. FCV2: Control voltage input for the cutoff-frequency (with attenuator).
  4. QCV: Control voltage input for the resonance of the filter (with attenuator).

Outputs:

  1. Audio Out: Output of the filter.

Controls:

  1. Lev.: Attenuator for the audio input.
  2. Frq.: Controller for the cutoff-frequency.
  3. FCV: Attenuator for the control voltage input “FCV2”.
  4. QCV: Attenuator for the “QCV” control voltage input.
  5. Res.: Controller for the resonance (self-oscillation) of the filter.

One for all

This is one of those filters where you can hardly go wrong: the SSM somehow always sounds good and usable, is never obtrusive or difficult to handle (in contrast to the filter resonance of the A-102 diode filter, for example). The bass is not reduced quite as much when resonance is used as with other 24dB filters. Classic sound.

Tips

In addition to its “historical” sound, the filter becomes interesting due to the voltage-controllable resonance: Assign a track of a sequencer line to the “QCV” input, so that very lively accents can be set.

Sound examples

  • A-105 / Modulation of Resonance

    In this example, the sawtooth outputs of three A-110-1 VCOs are used, with one VCO transposed down an octave. The filter cutoff-frequency of the A-105-1 is modulated by an A-140 ADSR, the pitch of the VCOs and resonance of the filter (“Q”) are controlled by an A-155 sequencer. To demonstrate the (in my opinion) very pleasant overdrive of the A-105-1, the input volume is increased as the track progresses.

    Sequence with modulation of resonance.

Technical specifications

Width8 HP
Depth45 mm
Power requirements30 mA (+12V) / -20 mA (-12V)