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Radio Modifications

Realistic DX-394

Realistic DX-394

Power Supply Mods


Introduction

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.

Circuit Diagram
DX-394 Power Supply Modifications


Parts List
Component Type Value Quantity
Ceramic Capacitor 0.1uF (104) 50V 2
Electrolytic Capacitor 2200uF 25V 1

The small blue capacitors are resin-dipped high quality multilayer plate ceramic.

Procedure
Power Supply Modifications

Mounting the Reservoir Capacitor
Power Supply Modifications

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.

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