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audio production powered by DC-DC??

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bluelaser

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Hi,all:
I make an audio production powered by DC-DC circuit. the specication of dc-dc is : input:8vDC---12VDC ,output:13.5VDC. the max current is 1A.
the chip is Max1771.
now I meet the problem:
a)when the speaker use the same ground with this unit. I can hear the noise. the frequency of noise is the same as the frequency of DC-DC.
b)when the unit boot up, I can hear the noise come from the motor of hard
disk .
Do you think whether it is suitable to use dc-dc power in the audio productio. or these problems are caused by the wrong pcb layout?

I hope your help !!!


Thank you!
bluelaser
 

Marky

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Use additional filter on output voltage (coil+capacitor). If you can, show schematic you use (only part of DC-DC). In application note, Maxim suggest inductor about 22uH and low ESR capacitor. And working freq is about 300kHz (you can't hear it 8O at normal operation)
 

bluelaser

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this is the schematic.
 

shanren

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hi,i have some experience:
1:13.5v output need a big capacitor,such a 2200u-10000u elec capacitor;
2:do not use a low ESR capacitor of c2,it is easy to cause unstabiliable;
3:use more large elec capacitor parallel a low ESR,such as a 2200u-10000u+1u MKT,it is good for audio;
4:separate the power amp ground from motor,it will reduce the noise from motor;
5:parallel a low esr cap in the motor,can also reduce the noise from motor.
hope this can help you.
 

bluelaser

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Thank you!
Now ,I try your methods at once.
 

Marky

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DC-DC

check working freq of DC-DC also. If is below 20000 Hz, you have to change it. Are you using 22uH coil ?? (rather bigger size for this current with ferrite core - not power iron ).
 

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