A-143-9

Voltage Controlled Quadrature LFO / VCO

Module A-143-9 is a derivative of our planned thru-zero quadrature VCO. It is a voltage controlled sine LFO with 4 outputs. The phase shift between the outputs is 90 degrees. The sine shifted by 90 degrees is also called cosine, the sine shifted by 180 degrees is nothing but the inverted sine, and the sine by 90 degrees is nothing but the inverted cosine.

The frequency range is from some minutes to frequencies beyond audio with three ranges selected by a toggle switch:

switch position H: about 30 Hz ... 3.5 kHz with the manual frequency control ("Frq."), beyond 20 kHz with additional external CV
switch position M: about 1 Hz ... 150 Hz with the manual frequency control ("Frq.")
switch position L: about 0,1 Hz ... 10 Hz with the manual frequency control ("Frq."), down to several minutes with additional external CV
Two exponential frequency control inputs are available: CV1 without attenuator and CV2 with polarizer. Consequently the module can be used even as an experimental sine VCO but does not feature an exact 1V/oct CV input! The precision CV input will be left to the thru-zero quadrature VCO.

Two LEDs display the positive and negative share of the sine output.

The core of the module is a so-called quadrature circuit that generates a sine a cosine signal with very low distortion. The quality of the sine/cosine signals are much better than those generated by a waveform converter with a sawtooth or triangle signal as starting point.

The output levels are about 5 Vss (+/-2.5V) but can be adjusted internally by a trimming potentiometer (P5 "Shape").

http://www.doepfer.de/a1439.htm