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Old 8th September 2009, 08:04 PM   #1
preiter is offline preiter  United States
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Default F5 hum

One channel my my F5 clone (Peter Daniel's boards) is humming badly. The other channel is silent.

The hum happens only when I have a signal connected (whether or not signal ground is connected). I even get hum when I connect the signal in to star ground.

I measured the resistance between board ground and star ground at .2 ohms. There is only one ground connection between the board and star ground.

Any clues about how to go about diagnosing this?
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Old 8th September 2009, 10:15 PM   #2
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Try evaluating the noise with shorted inputs (hot to ground)
with the input grounds not externally connected to each other.

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Old 8th September 2009, 11:41 PM   #3
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The hum happens when there is no external connection and the right signal input is shorted to star ground.
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Old 8th September 2009, 11:51 PM   #4
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Then I would look for oscillation, if you have a scope.

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Old 10th September 2009, 02:44 AM   #5
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Quote:
Originally Posted by Nelson Pass View Post
Then I would look for oscillation, if you have a scope.

No such luck

Would oscillation be at 60 hz? I thought that was usually a high frequency thing.
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Old 10th September 2009, 04:36 PM   #6
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Yes, it's a high frequency thing. The hum or buzz is just
the part you get to hear.

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Old 10th September 2009, 06:47 PM   #7
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I think I found it. It's just a poor ground connection. The crimp-on ring connectors I used to connect all of the wires to star ground aren't making a very good electrical connection.

To find it, I connected a wire to the working channel's signal input and probed around with the other end to find out what wires hummed and what didn't. In the absence of a scope you have to get creative.
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Old 3rd June 2012, 12:49 PM   #8
Charly1 is offline Charly1  Australia
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Even my problem is similar. U use cilvier F5 board and Jims 2 power boards for each channel. When there is no input its great no noise at all ver clean. As soon as connect CD player or preamp it start humm. Any practical experience on this and solution?
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Old 3rd June 2012, 12:58 PM   #9
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Are the rca jacks isolated from the chassis?
A picture would help though
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Old 3rd June 2012, 01:07 PM   #10
Charly1 is offline Charly1  Australia
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Melon. U refresh my brain. I made two amplifiers one raw allumium RCA ground was touching the ground it does not make the noise. Seems you give a vauluble point m second amplifiers I use proper box from Modushop. I think that RCA is not touchning the chasis. tmrw I will check that point. Highy appriciate ur feedback.
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