These amplifiers require bipolar power supply +15 V.
In APS-3205 (APS-3203) such bipolar power supply is provided by the connection of output sockets of two different channels in order to get a general output (pic.1). Such a connection is very similar to the connection of two batteries to get a general power output (pic.2).
It’s recommended to choose tracking – control mode in the power unit. In that case supply voltage change will be made simultaneously in two channels of the power supply and voltage in two amplifier arms will be the same respectively.