• 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 center 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 center 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 center position) or signal C (between center and cw position). In the center position no signal appears at the output. Similar to the two-way crossfader but without signal in the center 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 center position a mix of the signals A and B appears at the output. In the center position only signal B appears at the output. Between center 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 center position a mix of the signals A and B appears at the output. In the center position only signal B appears at the output. Between center 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 center detent and center terminal are used as controls.

Sub-unit 4 can be used optionally as a summing unit for the outputs of the devices 1-3. For this an internal jumper is available that connects the outputs 1-3 to the input of unit 4. The jumper connected to JP3 (factory setting) has to be removed and put on the pin header JP2. Then unit 4 becomes a mixer for the outputs of unit 1-3. For this application the switch of unit 4 has to be set to the left position or the control of unit 4 has to be moved to a position between B and C. Alternatively an A-138a/b mounted next to the A-138e can be used as summing unit for all four sub-units (2 wires have to be soldered to the A-138a/b). This document describes this option: A-138e_A138ab_connection.pdf

Applications:

• Attenuation of audio and control voltage signals
• Polarizing of audio and control voltage signals
• Two-way crossfading of audio and control voltage signals
• Three-way crossfading of audio and control voltage signals
• Two-way crossfading and polarizing of audio and control voltage signals
• Changing filter characteristics (e.g. lowpass to highpass)