A1439 Voltage Controlled Quadrature LFO/VCO
Module A1439 is a derivative of Doepfers planned thruzero 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 270 degrees is nothing but the inverted cosine. The frequency range is from some minutes to moderate audio (a few kHz) with three ranges selected by a toggle switch.
Two 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! Two LEDs display the positive and negative share of the sine output.
The core of the module is a socalled quadrature circuit that generates a sine and 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.
Typical applications:
 External sine/cosine oscillator for the frequency shifter A126
 Modulations with pure sine/cosine waveforms
 quadrature/barberpole effects
 experimental sine/cosine VCO

Many users suggested to add a common output level control, i.e. four VCAs with one common control (manual + CV without attenuator + CV with polarizer) for the output levels. This is why we also designed the Quad VCA module A1322 with the possibility of an internal default connection to the four outputs of the A1439 (no soldering required, short 10 pin flat cable with removable connectors on both ends).
The A1439 is also a meaningful addition for the Frequency Shifter modules A126 or A1262. It enables frequency shifting even below 50 Hz generating e.g. these mellow beat sounds with a few Hz frequency shifting only. The following document describes how to connect the old A126 and the A1439: A126_A143_connection.pdf. The new Frequency Shifter A1262 has sockets at the front panel available.
The thru zero version of the A1439 with temperature compensation is the module A1104.