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Old 28th February 2009, 08:35 PM   #1
diyAudio Member
 
Join Date: Sep 2006
Location: Malta, Europe
Default Hum problem

I have built a phono preamp with a TL-783 regulated power supply in a separate box. I still have a slight hum which seems to be coming mostly from one of the speakers. I changed the position of the valves but the problem remains.

The first filter cap -ve is connected to mains earth via a 27ohm hi-watt resistor paralled by a 0.22uF film capacitor. From the first cap it goes to regulator -ve and from there to the phono central ground point. The first and second phono stages are also separate and they each go to the central ground point.

The thing which is nagging me is that the two phono channels both share the same Ov busline. Is this OK or should I have made separate ground lines for each channel?

Any help or pointers to solve the problem will be greatly appreciated.

Joe A
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