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Old 30th June 2010, 06:56 PM   #1
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Default Lm3886 grounding made easy(?)

Ok...i am a newby and i am building my first dual channel lm3886 amplifier.

On each pcb i have the signal in ground(sgn-in-gnd),the speaker out ground(spk-out-gnd) and the power ground(pwr-gnd).

other grounds that also exist(not on the pcb!) are the main power ground(main-gnd) and the pot ground(pot-gnd).

1)I connect (main-gnd) on the chassis
2) points (sgn-in-gnd) and (pot-gnd) into a single point,lets say point1
3)point (pwr-gnd) goes on another point,lets say point2.

Then i connect point1 with point2.
Is that correct?

Where should i connect th spk-out-gnd?point1 or point2?

Please answer with the names used above cause im really confused..

Thnks!
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Old 30th June 2010, 07:06 PM   #2
Dr_EM is offline Dr_EM  United Kingdom
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Speaker return ground connects to point 2, the high current grounding point. Sometimes the low current grounding point (with signal input ground and pot ground) are linked to the main ground by a low value resistor, say 10r. Try a direct link between them firstly
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Old 30th June 2010, 07:14 PM   #3
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Thaks so much!

My last question is:Point1 and point2 have to be connected with the chassis or they are floating on the air?

Sorry for the english..
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Old 30th June 2010, 07:20 PM   #4
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Thaks so much!

My last question is:Point1 and point2 have to be connected with the chassis or they are floating on the air?
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Old 30th June 2010, 08:42 PM   #5
Dr_EM is offline Dr_EM  United Kingdom
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For safety the chassis should connect to safety earth if it is metal, the exception is if the unit is powered from an external double insulated power supply.

You should join the grounds to the chassis, join it at the power ground point (point 2) and ensure this is a good connection as it too acts as a safety earth route should the transformer insulation fail (a possibility in a toroid). Joining the metal chassis to circuit ground does effectively shield the electronics which is nice.

However, the consequence of all this is that the ground is tied to earth potential, which becomes an issue if the amplifier is used with other earthed equipment, such as a desktop PC. You may then experience a ground loop. Most CD players will not cause issue if connected to an earthed amplifier. Look here for more details on this:

Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

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Old 30th June 2010, 08:50 PM   #6
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Hmm i lost you..

Main power ground will be joined with the chassis.then i should join point2 and point1 to the chassis too?or just point2?
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Old 1st July 2010, 10:48 AM   #7
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Anybody knows if point1 and point2 should joined with the chassis or not?
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Old 1st July 2010, 11:24 AM   #8
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Anybody knows if point1 and point2 should joined with the chassis or not?
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Old 2nd July 2010, 02:28 AM   #9
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Hi - I posted up an answer to another thread you started with the same question here:

lm3886 grounding made easy(?)
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Old 2nd July 2010, 02:48 AM   #10
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Hi and thnx for the reply,

I think that signal-in-gnd, speaker-out-gnd and pwr-gnd are indepedented on the pcb. But i will check again when i go home.

what about my last question?
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