Module A-138e contains four identical units that can be used for different crossfading, mixing and polarizing applications:

Polarizer: only input A is used, inputs B and C are unconnected. In this case the sub-unit works as a polarizer. In the CCW position of the control the signal connected to input A appears at the output, in the CW position the inverted signal, in the centre position no signal appears at the output

Two-way Crossfader type 1: Two different signals are connected to the inputs A and C, switch is in the left position (switching contact of input B is open). In this case the sub-unit works as two-way crossfader between the two signals connected to the inputs A and C. In the centre position both signals appear with the same level.

Two-way attenuator: Two different signals are connected to the inputs A and C, switch is in the right position (switching contact of input B is connected to GND). In this case control is used to attenuate signal A (between CCW and centre position) or signal C (between centre and CW position). In the centre position no signal appears at the output. Similar to the two-way crossfader but without signal in the centre position.

Three-way Crossfader: Three different signals are connected to the inputs A, B and C. In this case the sub-unit works as three-way crossfader. In the CCW position only signal A appears at the output. Between CCW and centre position a mix of the signals A and B appears at the output. In the centre position only signal B appears at the output. Between centre and CW position a mix of signals B and C appears at the output. In the CW position only signal C appears at the output.

Two-way Crossfader / Polarizer type 2: Two different signals are connected to the inputs A and B. In the CCW position only signal A appears at the output. Between CCW and centre position a mix of the signals A and B appears at the output. In the centre position only signal B appears at the output. Between centre and CW position a mix of signals B and inverted signal A appears at the output. In the CW position only the inverted signal A appears at the output. Useful for CV mixing: e.g. signal A = ADSR, signal B = LFO. In this case one can fade between ADSR ... LFO + ADSR ... LFO ... LFO - ADSR ... - ADSR.

In addition, the inverted signal of input A is available as a separate output. Potentiometers with centre detent and centre terminal are used as controls.