Low-Pass Filter 6 / 12 / 24 / 48 dB
Module A-108 is a completely new voltage-controlled low pass / band pass filter based on the well-known transistor ladder (Moog ladder). The module has an internal 8-stage low-pass filter with different slopes to select from: 6, 12, 18, 24, 30, 36, 42 and 48 dB per octave. Of these 8 available levels, only the outputs of levels 6, 12, 24 and 48 dB are routed to outputs. These appear to us to be the most useful setting arrangement, as the differences are clearly audible. For example, the difference between 24 dB and 32 dB, or between 42 dB and 48 dB is hardly audible. If, however, you need one of the other filter stages to be available as an output, this can be changed internally.
Note: Only 4 output stages are available, which are set in the manufacturing process to the filter levels 6, 12, 24 and 48 dB. By changing the internal connections (jump wires), each of the filter stages can be set to an output, but only four at any one time. A multiway switch could be used, but the preinstalled factory settings (6 / 12 / 24 / 48 dB) represent the best combination – For example: having as simultaneous outputs the slopes 36, 42, and 48 dB make little sense from a music standpoint.
The resonance (or emphasis) can be adjusted manually right up to self-oscillation, in which case the filter will behave like a sine wave oscillator. An external input (feedback) is available for the resonance, which is fed internally to the 48 dB output if no cable has been plugged into the feedback socket. Any other modules can be looped into the feedback path (e.g., a VCA for voltage-controlled resonance or phaser-/ frequency sliders for phase / frequency shift effects).
The frequency is manually controlled (frequency control), via 3 control voltages (CV1, CV2, CV3), whereby separate attenuators are available for CV2 and CV3.
The audio input is sensitive enough that distortion is possible even at normal A-100 levels (e.g., VCO output). In the case of excessive distortion levels and simultaneous self-oscillation (sine oscillator), the self-oscillation will start to decline. This can also be implemented for additional stylistic means.
In combination with the A-135 voltage-controlled mixer and the A-144 morph controller, a filter with a voltage-controlled slope of 6 … 48 dB can be achieved.
- Low-pass: 6 / 12 / 24 / 48 dB
- Width: 12 HP / 60.6 mm
- Depth: 75 mm (measured from the rear side of the front panel)
- Power requirement: +40 mA (+ 12V) / -40 mA (-12V)
