Doepfer A-101-1 Vactrol Steiner Filter

Doepfer A-101-1 Vactrol Steiner Filter

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The module A-101-1 is a special multimode filter based on an idea by Nyle A. Steiner from 1974. The design is based on the standard single-feedback (non-inverting) filter standard circuit, where the different filter types are created by injecting the audio signal at different points on the circuit. Therefore, this filter has its own input for the low pass (LP), bandpass (BP) and high pass (HP)(!) and a common output, where all three input signals appear simultaneously. It is thus possible to simultaneously feed 3 different audio signals into this filter, which are summed up at the output and appear in different filtering (lowpass / bandpass / highpass).

In contrast to the original circuit, the A-101-1 uses Vactrols instead of diodes as variable resistors for frequency control. Due to the "crooked" characteristics of the Vactrols, the filter does not have a precisely defined control characteristic (eg V / octave). The inevitable tolerances of the Vactrols will also make each module sound a bit different and show a slightly different resonance behavior. The resonance control is also executed with Vactrols, so that this parameter is also voltage controllable.

Brand new with warranty.


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