A-138s is a simple but useful 4-in-2 mixing tool. It has four inputs available. Each input is equipped with an attenuator (Level) and a panning control (Pan) which is used to distribute the signal to the left and right output. In the center position of the Pan control the corresponding signal is distributed with equal levels to the left and right output (OUT L and OUT R). In fully CCW position the signal appears only at the left output (OUT L), fully CW only at the right output (OUT R).

Beyond stereo mixing it is equally suited to create variable parallel routings. For example: Any of the four inputs may be routed in variable intensity to feed two filters.

You may regard the A-138s as a smaller version of the A-138m Matrix Mixer.

Inputs and outputs are DC coupled, i.e. the module can be used for the mixing of control signals too.

Technical notes:
The amplification with Level fully CW and Pan at center is about 1.6 for both outputs.
The amplification with Level fully CW and Pan fully CW is about 1.9 for the right output and zero for the left output.
The amplification with Level fully CW and Pan fully CCW is about 1.9 for the left output and zero for the right output.