The CGS757 Bi-N-Tic Filter is a strange mixture of a VCO and a switched capacitor filter based on the filter presented by Jan Hall in Electronotes. If you are after something different, this fits the bill. After all, how many filters have a sync input?
A VCO drives a pair of analog switches, switching two banks of eight capacitors across op-amps, creating a multi-passband or comb filter at f0, f1, f2, etc. Two controls are provided within the structure of the filter - damping and bandwidth. Not all combinations of these two are actually valid, some resulting in silence, but none the less, quite an array of variations is possible.
The VCO is connected via a signal processor to the input of a binary counter, creating divisions. The first three divisions are used to drive the pair of analog switches. The remaining divider outputs are also available via the Feedback rotary switch. This is passed through a level knob and fed back into the input of the filter itself, thus giving the filter an excitation signal that is perfectly in sync with its operating frequency. This causes the filter to become a very unusual oscillator, giving quite complex waveforms or even simple waveform sequences (ringing bursts). There is also an "Excite" input for using external signals to excite the filter, select X on the Feedback switch to engage it.
- Logarithimic FM (1V/Octave) Input
- Linear FM Input
- Sync Input
- Coarse Tuning Knob
- Fine Tuning Knob
- Feedback switch: Selects excitation signal to be fedback in to the filter
- 6 Feedback modes: Choose between 5 different divisions of the VCO frequency or an external signal
- Feedback level knob
- Damper control knob
- Bandwidth control knob
- Excite (X) input: Input external excitation signal to be used by the feedback section
- Signal Input
- Signal Output
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- Eurorack Module
- 15 HP Wide
- +12V: 5 mA current draw
- -12V: 5 mA current draw
- 11.2 cm deep