60Hz buzzing

[Salas]

So you have a PSU ground and no signal ground to chassis. Please get crocodile clips and a 10 Ohm resistor. Attach one clip to an input RCA ground side and through the 10R attach around to chassis and see what happens. Do L&R channels test zero R when you probe L & R input RCA ground sides?

 

[jrevillug]

(unless of course you are in Europe or using 240 where they are both hot.
[/B]

Here in Europe, despite using 240V, only one of our lines is hot- we don't have the + and - 120v and ground thing going on that you have in the states, IIRC.

 

[Colt45]

Here in Europe, despite using 240V, only one of our lines is hot- we don't have the + and - 120v and ground thing going on that you have in the states, IIRC.

ding ding

 

[whitelabrat]

Once again thanks everyone for their help!

I double checked the polarity going into the power transformer. Oll Korrect there.

I then connected a 20ohm resistor to the input ground and then to the chassis. Most of the buzzing disappeared. Just a very low warm hum remained.

 

[whitelabrat]

This is an interesting discussion on ground loops.

http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm

I suppose I should hunt for a voltage drop somewhere in the circuit? Should I ground the inputs to the earth via resistor? I'm not sure about the latter, but I think I need to check the voltage in the circuit?

In the circuit, could a bad capacitor cause this sort of problem?

 

[EC8010]

It's a very sharp buzz rather than a mellow hum. Not that it makes a difference.

Oh yes it does. A sharp buzz suggests problems with reservoir capacitor current pulses producing voltages where they shouldn't. There should be one loop connecting the reservoir capacitor to the rectifier and the load should be connected across the capacitor - never anywhere inside the loop.

 

[Salas]

Once again thanks everyone for their help!

I double checked the polarity going into the power transformer. Oll Korrect there.

I then connected a 20ohm resistor to the input ground and then to the chassis. Most of the buzzing disappeared. Just a very low warm hum remained.

Way to go! Ground loop Zzzz nailed. Now hunt around that PSU ground related hum. Is there any connection to chassis from negative post of 1st smoothing PSU cap?

 

[whitelabrat]

Further tests show that connecting a source and attaching the input ground to the chassis cuts the buzz and provides a good clean signal. The multimeter shows 13Vac moving over the ground. I couldn't get a current reading with my meter. Very good!

 

[Salas]

See what is best. Test 0R, 3R3, 6R8, 10R also. Maybe the 20 Ohm you used already proves best, maybe there is better.