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Old 20th August 2007, 09:04 PM   #1
sts9fan is offline sts9fan  United States
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Default another Hum issue LM3875

So I have built up the first channel for my stereo LM3875 kit from audiosector. I decided to test it out and see if it works and it does but it is also humming like crazy. I currently only have the safety ground hooked up. The signal ground is not connected. It also has the hum with no source connected. I tried a cheater plug (not to use just as a test) and the hum was still there.
Now I generally have no idea what i am doing so I am not sure how to test this thing. I am not sure where to take measurements to see if I am getting proper voltage etc. Any help would be great.
Thanks
Kris
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Old 21st August 2007, 12:33 AM   #2
BWRX is offline BWRX  United States
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The source/signal ground needs to be connected to the power ground.
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Old 21st August 2007, 02:48 PM   #3
sts9fan is offline sts9fan  United States
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thanks I will try that today
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Old 21st August 2007, 03:00 PM   #4
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You may find some info how to wire the kit here:
http://www.diyaudio.com/forums/showt...20#post1108820
http://www.diyaudio.com/forums/showt...773#post787773
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Old 21st August 2007, 03:23 PM   #5
sts9fan is offline sts9fan  United States
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Looks like the only thing I have different is I don't have the chassis ground connected. Could this be the cause of the hum? If I connect it and it is still humming what should I look at next?

thanks
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Old 21st August 2007, 05:48 PM   #6
Nordic is offline Nordic  South Africa
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Make sure input RCA sockets are isolated from case...
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Old 22nd August 2007, 04:36 AM   #7
traw is offline traw  United States
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take a snapshot of your connections - it will be easier to see. lack of chassis connection likely not cause, the center tap or shared ground from the transformer anchors the 0V.
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Old 22nd August 2007, 12:56 PM   #8
sts9fan is offline sts9fan  United States
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will do thanks. The transformer I am using is a AnTek AN-3222
http://toroid-transformer.com/
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Old 28th August 2007, 09:02 PM   #9
sts9fan is offline sts9fan  United States
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Here are some pictures. Hopefully they can help.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Thanks for any help!

Kris
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Old 28th August 2007, 09:41 PM   #10
sts9fan is offline sts9fan  United States
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http://travel.webshots.com/photo/222...86056042namwJw
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