Module A-138i is a four channel mixer with an additional mute switch for each input. On top of that it is equipped with two types of single outputs and a dual mix output.  All inputs and outputs are DC coupled. Consequently the VCAs can be used to mix both audio and control voltages.
Each input is  - apart from the mute switch - equipped with the usual attenuator.
The single outputs offer the attenuated and possibly muted signal of the channel in question. Two version of single outputs are available:

• Single Output A: If a plug is inserted into the single output "A" socket the channel in question is removed from the sum signal.
• Single Output B: If a plug is inserted into the single output "B" socket the channel in question is not removed from the sum signal. This type of single outputs is available only for the channels 1 and 2.

The output is twice available (two sockets, hard-wired like a multiple).