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Old 15th August 2010, 07:45 AM   #1
liquias is offline liquias  Israel
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Default ground noise

Hi,
I am building an MP3 decoder player using the VS1011 chip.
the IC datasheet specifically mentions separating the grounds for digital and analog signals. If i follow this guideline everything seems to work fine.

However i am bound to using only one power source (a 12V battery).

If i am using headphones everything works like a charm. but when i am connecting the signal out to an amplifier I get tons of digital noise through the ground (zero , or common) wire.

it's a 12V DC power supply. using a 12V battery (3.5 A/Hr).

I am looking for some kind of circuit that will be able to simulate two separate power supplies from one power source.

any ideas ?

Last edited by liquias; 15th August 2010 at 07:55 AM.
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Old 15th August 2010, 02:26 PM   #2
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This is as good a staring point as you can find:

Henry Ott is the top reference.

Grounding of Mixes Signal Systems
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Old 16th August 2010, 11:33 AM   #3
marce is offline marce  United Kingdom
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And if you dont know what your doing dont split them!
A schematic would be useful.
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Old 16th August 2010, 12:31 PM   #4
liquias is offline liquias  Israel
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Default Yes,

I read the article and few other articles related (some by Mr. Henry Ott and some by others...) to the one offered by Speedskater (Thank you), and I understood that separating ground planes is wrong.

I cannot seem to get rid of the awful digital squeal for now, however this is not very surprising since the whole project is assembled on a conducting matrix and is far from being ideal at the moment.

I'll be sure to follow the guidelines offered in these articles when i'll design the PCB. I hope this will minimize (or even completely solve) my problems.

I can't figure out though why is it that when i'm using earphones I get no squeals what so ever.

As this is a system i'm still tweaking and tampering with i don't have the exact schematics written down just yet (i'm doing this project with a friend and we changed the CPU from one model to another...), however this project is based on the project by Mr. Rephael Abrams (the Sakura design) that can be found here:

Index of /~raphael/mp3/MMC_version

schematics (very close to what we're doing) can be found here :
MMC_mp3

Hope this helps ,
Liquias.
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Old 16th August 2010, 01:44 PM   #5
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I've had this problem using DC-DC converters --- oftentimes a inductor of a few microHenries on the power lines is going to help, you can also bypass the input of the amplifer with a 150pF capacitor to knock down RFI. In addition to the steps taken on the PCB, it's good to make sure that the chassis which surrounds your project is properly grounded. David Davenport's article is a great synthesis of Ralph Morrison's books on grounding technique: Audio Component Grounding and Interconnection
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