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60Hz buzzing
60Hz buzzing
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Old 17th May 2007, 06:45 PM   #21
Salas is offline Salas  Greece
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60Hz buzzing
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?
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Old 17th May 2007, 07:24 PM   #22
jrevillug is offline jrevillug  United Kingdom
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Quote:
Originally posted by frank754
(unless of course you are in Europe or using 240 where they are both hot.
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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.
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Old 17th May 2007, 09:47 PM   #23
Colt45 is offline Colt45  Serbia
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Quote:
Originally posted by jrevillug

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
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Old 18th May 2007, 02:28 AM   #24
whitelabrat is offline whitelabrat  United States
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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.
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Old 18th May 2007, 06:38 PM   #25
whitelabrat is offline whitelabrat  United States
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This is an interesting discussion on ground loops.

http://www.dself.dsl.pipex.com/ampin...s/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?
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Old 18th May 2007, 06:44 PM   #26
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by whitelabrat
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.
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Old 19th May 2007, 02:37 PM   #27
Salas is offline Salas  Greece
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60Hz buzzing
Quote:
Originally posted by 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.

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?
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Old 21st May 2007, 06:37 PM   #28
whitelabrat is offline whitelabrat  United States
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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!
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Old 21st May 2007, 08:23 PM   #29
Salas is offline Salas  Greece
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60Hz buzzing
See what is best. Test 0R, 3R3, 6R8, 10R also. Maybe the 20 Ohm you used already proves best, maybe there is better.
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