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Old 24th May 2006, 07:49 AM   #1
diyAudio Member
Join Date: May 2006
Post Lm1875, Emc Protections

Dear Friends,

I am the hardware engineer in the company and I have not too much experience in sound designs!!

I have testing the single supply circuit that is inside the lm1875 datasheet, and it sounds ok.

I have to put all the circuit in a box with and speaker and we have to test that this box is acording EMC rules.

Do you know if there is any input/output EMC filter to add in the single supply circuit above mentioned?

What is the best way to desing the properly Heat Sink for the LM1875?

Thanks in advance!!!

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Old 24th May 2006, 12:37 PM   #2
joensd is offline joensd  Germany
diyAudio Member
Join Date: Dec 2001
Location: Germany
Are you talking about interference or susceptibility?
For lowering conducted susceptibility(+interference) you could add one of those "AC-input-filter":
Those sometimes can be had quite cheaply at buyouts.

For improved susceptibility I´d definitely put it in a metal case,
that is properly grounded.

Otherwise you just have to finetune your PCB-layout and schematic so that the chip doesn´t oscillate.
(see datasheet and/or check the forums)

Don´t see many other problems that could occur.
The chip has a good PSRR and seems quite easy to handle.

PS.: Don´t know about EMC rules being different in other countries so maybe you could kindly ask other commercial amp designers here.
You should find some searching around ;-)
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Old 24th May 2006, 02:32 PM   #3
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Join Date: May 2006
Can your recommend me one "AC-input-filter"?

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Old 24th May 2006, 05:07 PM   #4
joensd is offline joensd  Germany
diyAudio Member
Join Date: Dec 2001
Location: Germany
Can your recommend me one "AC-input-filter"?
Unfortunately not.
I´ve got some around but wouldn´t know exactly what to look for.
Guess they all damp those interferences to a certain extent...

That said: there are quite a few amplifiers out there without those,
so passing EMC norms shouldn´t depend on those filters.

Get the circuit properly working; metal case, proper grounding
and do some tests.(oscillations?, conducted EMI-tests)
If there´s any problems go from there.

What do you mean exactly with EMC protections?
Do you know which tests the amplifier has to go through?
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