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Old 3rd June 2003, 12:59 PM   #1
JCoffey is offline JCoffey  United States
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Default How to get rid of hum?

I have an amp that I purchased about 6 years ago for around $100, that is a really nice sounding little amp made for Computer sound systems( although it makes a great little integrated, with a bypass for the EQ). I just found out last night that it uses 2 LM3876 chips. Problem is, it hums. It's not very quiet at all. I really like the sound, but dont like the noise. I snapped some pics of it last night, and was wondering if some of you gurus can look at the pics of the layout, wiring and topology and come up with suggestions of things to check. I looked at the grounds a couple years ago, and tried to clean them, but it do any good. Any other suggestions?
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Old 3rd June 2003, 01:05 PM   #2
JCoffey is offline JCoffey  United States
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Here's the front. Aint pretty, but it works.
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Old 3rd June 2003, 01:07 PM   #3
JCoffey is offline JCoffey  United States
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Heres the topology. They transformer makes this little thing weigh a ton.
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Old 3rd June 2003, 01:09 PM   #4
JCoffey is offline JCoffey  United States
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Heres the pair of LM3876TF chips
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Old 3rd June 2003, 01:10 PM   #5
JCoffey is offline JCoffey  United States
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Herss the Preamp, eq section.
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Old 3rd June 2003, 01:12 PM   #6
JCoffey is offline JCoffey  United States
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Here are the inputs.
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Old 3rd June 2003, 05:10 PM   #7
JCoffey is offline JCoffey  United States
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Anyone?
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Old 3rd June 2003, 05:17 PM   #8
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I have one suggestion for you...unscrew that input board at the back and look for some cold solder joints on the bottom.....I had a sony A/V receiver that was humming every once in awhile.....I touched up all the joints and never had a problem again


Cheers!!The DIRT®
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Old 3rd June 2003, 06:54 PM   #9
JCoffey is offline JCoffey  United States
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at the risk of sounding like a NOOB, What do you mean by a cold solder? I notices that night that one of the 4 blue caps by the ICs, is loose on the board. I need to fix that right away. i'm just curious if all the little gizmos, like the output level leds, the eq, the eq bypass, Sub out Mike in, etc is causing too much interference.
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Old 3rd June 2003, 07:03 PM   #10
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I was referring to a cold solder joint...it can happen after repeatively plugging in and out at the back.....if you have a loose capacitor then definately solder that.....while your at it inspect the rest of the bottom of the board and touch up any joints that dont look good....its just something simple causing your noise....the amp is definately worth fixing it has a hefty power supply

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