Brian Powell Audio

Crimson 640 Power Amplifiers

First produced in 1999, these are mono blocks with a 175W output power in to 8 Ohms. They feature two large toroidal transformers and PCB with 4 hefty power devices.

There is a small internal fan which improves cooling by 25%. Due to an oversight and the UK being so cold there was a slight oversight on fan operation. The internal thermostat switch can permit the fan remain on permanently in error if used in a hot environment. The fan switch was originally a 40/25 C degree one. It should be replaced with 60/45 C one.. This switch is of the normally open type. Fan ballast is a power resistor from the +60v rail. The cooling of the finned heatsink is further assisted by an aluminium heat coupler plate to shunt heat to the outer aluminium sleeve.

Early 640s had matched transformers and a single rectifier. Later ones had dual rectifiers.

Mains voltage is hard wired, but the transformers do have twin 115V primaries.