A power transformer that has a 120VAC rms primary and a secondary voltage of about 11.3VAC rms (about, to allow for two diode voltage drops), a diode bridge rated to handle tens of amps of currnet and some large electrolytic and film filter capacitors will make a basic 14.4VDC power supply. A power switch, fuse, and indicator light for the primary of the transformer would be nice also. A safe case, with venitlation, would be nice, too.

Beings this basic supply is not regulated (a suitable regulator circuit will add a lot to the cost), significant ripple voltage will exist on the DC voltage. This ripple voltage will increase as the load on the supply increases (playing the amp and speakers louder).

In order for this ripple voltage to not be heard as a hum in the speakers, the amp's DC-to-DC converter (to generate the higher DC voltage(s) that the amp circuit itself needs) needs to have a good (high) power supply rejection ratio (PSRR), which is the circuit's ability to reject variations in the input 14.4VDC and just do it's job. The amp itself should have a high PSRR, and probably will if it is a high feedback design.

Paul