Doepfer A-126-2 Frequency Shifter Eurorack Module

The A-126-2 CV Frequency Shifter II from Doepfer is a completely analog frequency shifter. Even though the module is specialized in changing frequencies, it has nothing in common with a pitch shifter. The Frequency shifter shifts all frequencies of the incoming audio signal to the same frequency. For example, if the shift frequency is 200 Hz, 1000 Hz becomes 1200 Hz, 2000 Hz becomes 2200 Hz, and so on. The frequency range of the internal quadrature VCO is about 8 octaves and can be used as an external VCO if required.

The A-126-2 is a complex circuit consisting of a preamp, quadrature oscillator (sine & cosine), envelope follower, dome filter, two ring modulators, inverter, comparator and several VCAs. The Squelch knob controls the modulation of the main VCA between envelope follower and open. Mix sets the ratio of the frequency shift down respectively up. For the oscillator frequency, Mix, VCA as well as sine and cosine there are separate CV inputs, two of them have their own attenuators.