CGS Bi-N-Tic voltage controlled filter/oscillator (previous version): Difference between revisions

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A VCO drives a pair of analog switches, switching two banks of eight 0.047uF (47nF) capacitors across op-amps (effectively creating multiple integrators), and this a multi-bandpass or comb filter is created at f0, f1, f2 etc.. The overall filter configuration itself should be easily recognized. 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.
A VCO drives a pair of analog switches, switching two banks of eight 0.047uF (47nF) capacitors across op-amps (effectively creating multiple integrators), and this a multi-bandpass or comb filter is created at f0, f1, f2 etc.. The overall filter configuration itself should be easily recognized. 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 section has been re-vamped, based on the well known [http://www.synthsource.com/ens76/vco.html Electronotes ENS-76 VCO Option 1]<ref group="note">''ENS-76 VCO Option 1'' by Hutchins, Bernie,Terry Mikulic, Electronotes No. 75, March 1977, pp. 6-9. and fig. 4-9, p. 94</ref> as used in the [http://rubidium.dyndns.org/~magnus/synths/friends/stopp/ ASM-1], etc. This core was an obvious choice due to the amount of information, lists of suitable substitutes and so on that are available on the web. In this case, a cut-down version is used as its purpose was simply to drive the analog switches. The VCO is connected via a signal processor to the input of a 4024 binary counter. The first three divisions are used to drive the address lines of the 4051 analog switches.
The VCO section has been re-vamped, based on the well known [http://www.synthsource.com/ens76/vco.html Electronotes ENS-76 VCO Option 1]<ref group="note">''ENS-76 VCO Option 1'' by Hutchins, Bernie,Terry Mikulic, Electronotes No. 75, March 1977, pp. 6-9. and fig. 4-9, p. 94</ref> as used in the [https://web.archive.org/web/20190429023311/https://rubidium.dyndns.org/~magnus/synths/friends/stopp/ ASM-1], etc. This core was an obvious choice due to the amount of information, lists of suitable substitutes and so on that are available on the web. In this case, a cut-down version is used as its purpose was simply to drive the analog switches. The VCO is connected via a signal processor to the input of a 4024 binary counter. The first three divisions are used to drive the address lines of the 4051 analog switches.


While not shown on the circuit diagram, the remaining divider outputs are also available. They are not buffered, and are thus not suitable for connection to panel jacks, but they can be wired to a rotary switch, followed by a level pot, 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. When configured like this, the filter becomes a very unusual oscillator giving quite complex, waveforms or even simple waveform sequences (ringing bursts).
While not shown on the circuit diagram, the remaining divider outputs are also available. They are not buffered, and are thus not suitable for connection to panel jacks, but they can be wired to a rotary switch, followed by a level pot, 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. When configured like this, the filter becomes a very unusual oscillator giving quite complex, waveforms or even simple waveform sequences (ringing bursts).
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