Brian Powell Audio

Crimson 620 Power Amplifier

The 620 is a stereo power amplifier with a power of 40W+40W into 8 Ohms and some 60w + 60W into 4 Ohms and a sensitivity of 800mV. The 620 has mass of 4kg. PCBs in the early 620s were type 5, V, VI or VII. Early 620s have a captive mains cable but later ones have an IEC inlet. The 620 in the photo above shows a rebuilt 1980s unit with a refinished sleeve in fine crackle black powder coat.

After 2002, 620s were fitted with an inverter PCB to make better use of the power supply. These inverters had a fade-in mute like the 610 preamp. Some of the early inverters had no mute and were rather nasty at power up and power down. Some 620s had the extremely unsuitable DNM cable fitted as signal cable which should always be replaced with a twisted pair of 7/0.2.

Main PCBs were type VIII issue 1 up to VIII issue 4. Of late the PWR PCBs have been fitted.

Early 620s had red LED power indicators which later were changed to green as red came to indicate a standby condition or fault condition. Since 2004 the LED indicators have been bicolour. Normally green, these flash red at clip overload.

The output to the speakers was fuse-less but since 2021 speaker protection PCBs have been fitted in every case. If the amplifier is shorted the electronic shutdown operates and the output is muted. To reset, remove the mains for 10 minutes.

All 620s will shutdown to no LED indication at all if the heatsink reaches 70C. This will self-reset at 55C.

Mains voltage selection was hard wired but since 2023 some 620s will become available with 110/230 V switching. See photo below. It is intended to add a power outlet to run a small external fan once the heatsink reaches 60C. Later 620s have a coupling plate to shunt heat to the outer cover and so reduce the heatsink temperature.

The latest PCBs will give a massive upgrade to the 620s and this can be done with some small engineering changes to the heatsink inner surface.

Picture shows freestanding pluggable fan for full power operation into hard loads. It sits just in front of the heatsink vanes and plugs into the rear panel socket. Cooling is enhanced fan a factor of greater than three.