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Old 31st October 2014, 01:55 AM   #1
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Default request REAL HOW TO : to kill hum noise !

Hi ALL !

I request a HOW TO from electronics tech and engineer on this forum, after read many many thread about hum noise without a real and clear solution.

Many people have big trouble with LM chip amp hum noise and ground loop trouble.

1st solution = star ground. (no amplifier company have this and her amp are no hum).
2nd solution = add AC ground on case (not amp company have AC ground).
3rd solution = AC Emi filter. (this have no effect on ground loop)

I wait for REAL tips and hints (clear and simple for idiot like me !)

THANKS IN ADVANCE

nicK
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Old 31st October 2014, 03:10 AM   #2
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There's not a simple solution to solving noise issues. It could be as simple as reversing the phase on an AC plug or a huge project like staking ground in earth for a building.

If you want a place to start, I suggest reading about conductively coupled noise, coupling through common impedance, and shielding techniques.

Understanding how high frequency noise and low frequency noise creep into your circuit is important too. Low frequency noise takes the path of least resistance and high frequency noise takes the path of least impedance.

This might help:

http://www.analog.com/static/importe...0828AN_345.pdf
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Old 31st October 2014, 09:33 AM   #3
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The leaking magnetic flux from the transformer is also a source of hum.

Gajanan Phadte
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Old 31st October 2014, 11:35 AM   #4
tomchr is offline tomchr  United States
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My advice: Read up on ground loops, capacitive coupling, and inductive coupling. Study a little electromagnetic field theory to work out how to minimize the coupling mechanisms.

Morrison, "Grounding and Shielding Techniques" is a pretty good place to start.

You can also try to dust up a copy of Ott, "Noise Reduction Techniques in Electronic Systems". I seem to recall Morrison's book dealing more with the electromagnetics and coupling mechanisms specific to grounding, though.

You may also find some useful bits on grounding in the Grounding section of my Taming the LM3886 Chip Amp Page. Right now, the page mostly deals with grounding the chip itself, including a star ground example and an explanation of why star grounding is a really bad idea. I do, however, plan to expand the page to touch on some of the subjects you mention.

~Tom
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Last edited by tomchr; 31st October 2014 at 11:48 AM.
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Old 31st October 2014, 02:14 PM   #5
johnr66 is offline johnr66  United States
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Step 1: Identify where the source comes from. Short the input to ground and see if the hum remains.That gives a good starting direction.
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Old 31st October 2014, 06:00 PM   #6
AndrewT is offline AndrewT  Scotland
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Audio Component Grounding and Interconnection - diyAudio
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Old 1st November 2014, 03:02 AM   #7
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What about a ground loop with an amp inside a computer? My little tda7297 amp is powered by the 12v rail of the computer psu. When the source is the onboard audio card I get massive interference and can actually hear the processor.

Could this be fixed by grounding the input signal(to the amp) onto the computer chassis(earth ground)?
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Old 1st November 2014, 10:40 AM   #8
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Strange problems rarely have strange solutions. Most commonly, the more bizarre the problem, the more basic the cause. As a quick example, before you spend $3,000 rewiring your house try replacing the bulb.

You have noise in an amp. Only when a CD player or other audio source is connected? Then look to your connections or connecting cables--or the player itself.

Otherwise, speaking only of the problem amp, have you followed the rule of keeping the audio signal separate from power supply voltages?

Power supplies hum, of course they hum, they couldn't work if they didn't hum. But the hum (and other noise) is supposed to be filtered out so that only clean DC comes anywhere near the audio signal.

Power supplies are one thing, audio circuits are another thing, don't let them get mixed in your mind or on your circuit board. I hope the below circuit might illustrate the point.
.
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