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This filter’s unique feature is that different filter types are realized by injecting the audio signal at different points of the circuit. For this reason, the A-101-1 has three inputs with level control: one lowpass input which is normalized to the bandpass input, which itself is normalized to the highpass input. The level controls make it possible to mix the filters and to generate new filter types. e.g. with all three filter levels turned to maximum level you get a notch filter.
Furthermore, the cutoff frequency influences which filter type is “monitored”. This way you can blend from LP over BP to HP with increasing cutoff, known as “frequency scanning”. Interesting effects happen when three different audio signals are used because they are both morphed and filtered at the same time.
Vintage edition with black faceplate and custom knobs.
In contrast to the original circuit, the A-101-1 vactrols are used instead of diodes as variable resistors for frequency control
2 LEDs provide information on the currently set frequency and resonance
Width: 16 HP / 80.9 mm
Depth: 50 mm (measured from the rear side of the front panel)
Power requirements: +30 mA (+12 V) / -30 mA (-12 V)