This stereo power amp produced 40W per channel into 8 Ohms and 60W per channel into 4 Ohms. Gain was approx. x 30, requiring just under one volt RMS for full power.
- phono inputs
- 4mm binding post speaker terminals
- thermal cut-out 70C
- Fuse-less output with electronic shutdown if shorted
- captive mains cable 1.2m
- small frontal area 100mm high by 80mm wide
- minimum load 2.7 Ohms
- Re-wireable for 115V.
- PCBs fitted 35-01 issue 5
The later plastic power type PCBs (even PWR18 of 2024) can be retrofitted if extra holes are tapped into the heatsink.
Care needs to be taken with wiring to avoid magnetic field (hum) from the basic E-I type transformer. Due to magnetic field emissions, this unit needs to have least 150mm spacing from a Crimson preamp with a disc stage (further if an MC stage is used).
520 Updates
- It would be ideal to replace the transformer with a toroidal type. However, there will be acceptable residual hum if wiring is done correctly and the wire routing is optimised on test for minimum hum at the speakers.
- Replace the reservoir capacitors due to ageing
- Replace the PCBs. The later ones are much better sounding.
- Replace all connectors with gold flashed types.
- Brace the front heatsink to stop it being pushed back; the later amplifiers had the edges turned up to stiffen them.
- Add speaker protection PCBs to “crowbar” the output if the amplifier PB fails (and produces DC which rapidly does blow speakers).
- The rear switch is no longer a nuisance as a smart power socket (e.g. Alexa) can be used to power the amplifier on/off. The power switch can thus be left “on”. The rotary switch can be updated to a rocker which is more robust, but this is difficult.
- Replace the LED.
- The captive mains cable could be replaced with an IEC power socket but this is difficult.
- Float the signal ground from the chassis ground. Add a rectifier safety clamp. Break the internal ground loop with low value resistors. This is only needed if another piece of connected audio equipment is also mains grounded.