The IRP PA-Series Power Amplifiers are comprised of building-block modules. Each power amplifier module is constructed as a ½ of 1-RU device. Consequently, each dual channel (bridgeable to one mono channel) amplifier occupies only ½ of 1-RU. Two such modules mounted in a single (1.75 x 19 inch) rack space can provide four (4) audio output channels, 2 monaural (bridged) outputs or combination thereof. The ‘T’ version of these power amplifiers incorporate a built-in, internal mounted, tordial-wound constant voltage output transformer capable of driving either a 70.7 or 100 volt transmission line. The building-block concept of the IRP PA-Series amplifiers provides the capability, with minimum wiring configuration, to drive selected output channels at constant voltage while simultaneously operating other channel(s) at voice coil impedances.