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Topic: TS-22 Pentode Filterbank

Jack Hertz

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TS-22 is unlike any other "filter" or "filter bank" offered on the market. It consists of four simple vacuum-tube bandpass filters. Their center frequencies are offset by 1 octave from the previous filter. Each filter is independently sweepable with panel knobs; or they are all sweepable in unison, using either a panel knob or in external source of control voltage, such as an envelope generator or LFO. (A special optoisolator does the job.)

The TS-22 Pentode Filterbank contains four independent bandpass filters, made of simple "twin-T" circuit designs. They are each based around a pentode vacuum tube, giving a unique sonic effect. (They pass some of the raw signal through to the output, so your bass notes will be audible. Unlike those rigorously-designed solid-state filters, the TS-22 was designed to sound musical, not like a laboratory instrument.)

All four filters mix down to another pentode tube, which is used as a VCA (optionally). This is another design which was little used in the past--by applying the control voltage to the "screen grid" of the pentode, its gain can be varied--from total cutoff up to a gain of 100 or more. (It doesn't cut totally off, you might hear a very very low signal when you envelope is not triggered--this is normal. If total cutoff is demanded, which is not usually a requirement, the TS-22 may be followed by a noise gate.)

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