Power Supply Mods
When listening with headphones you can hear a constant low level hum in
the background. The hum is caused by AC ripple superimposed on the main
DC power supply, which is because of a lack of decoupling. This can be
corrected by adding a reservoir capacitor across the positive DC output
of the bridge rectifier D27, see circuit diagram. Additional high
frequency supply decoupling is provided by two small ceramic capacitors.
|0.1uF (104) 50V
|The small blue capacitors are
resin-dipped high quality multilayer plate ceramic.
Mounting the Reservoir Capacitor
Fitting the Ceramic Capacitors
Using a double layer of 'Quick Stick' pads mount a 2200uF 25 Volt
electrolytic capacitor at the position shown in the photo. With its
negative lead to the negative connection of the bridge rectifier D27 and
its positive lead to the outher side. Place a 0.1uF(104) ceramic
capacitor across D27 and C144.