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Old 25th November 2011, 10:26 PM   #1
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Default Need to clean up computer p/s noise

Hi,

I am building a arcade system and am trying to use the computers power supply to provide the +12v that I need to run a chip amp I have built. I'm using the TDA8561q that I pulled from a car stereo and the amp sounds great when connected to my ipod. However, when I connect it to the computers sound card output I get all kinds of "digital noise". I tried using a couple of small isolation transformers on the amps inputs and that has cleaned most of the noise up. However, when I'm running a game I still get alot of buzzing that is very annoying. Without trying to squeez another small power supply into this cab, I would love a solution to this problem.

Any help would be greatly apreciated.

Here is the link to my chipamp...I'm using the BTL setup.

http://www.nxp.com/documents/data_sheet/TDA8561Q.pdf

Thanks,
Wade
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Old 25th November 2011, 11:43 PM   #2
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Switch mode supplies are notoriously noisy. First try a big choke in series with the 12v.
Doc
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Old 26th November 2011, 01:04 AM   #3
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Quote:
Originally Posted by thaumaturge View Post
Switch mode supplies are notoriously noisy. First try a big choke in series with the 12v.
Doc
Thanks for your reply...I don't know what you mean by large but I found the largest one I had and connected it and it didn't make a difference.

and other suggestions?
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Old 26th November 2011, 05:07 AM   #4
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Noise might be RF coupled. Try putting a ferrite block around your PS leads (Like the round blob on computer cables. Has a hunk of ferrite in it that blocks RF noise.) After that a secret weapon noise supressor is a hundred ohm resistor in series with various values of caps conected across the supply leads. Start with say a .1uf and work up. Different combinations will filter different noise characteristics.
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Old 26th November 2011, 06:30 AM   #5
sandyK is offline sandyK  Australia
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Try a large value low ESR electro after the choke as well..
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Old 26th November 2011, 08:06 AM   #6
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Hi
What sound card does the computer use. If it is an integral one what chipset does it use. the reason i ask is i have tried lots of diffrent sound cards motherboards and psu's over the years and have found some sound cards are noisey as hell. And more so when running extensive graphics applications .

Regards Ian

Last edited by madtecchy; 26th November 2011 at 08:09 AM.
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Old 26th November 2011, 08:15 AM   #7
jitter is offline jitter  Netherlands
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I agree with madtechhy. If the buzzing is already in the audio signal, you can try and clean up the PSU as much as you can, but it will only make a difference for PSU noise.

I don't use the analogue output of the integrated soundcard of my PC, every action of the PC is heard (even something like moving the mouse!) in the sound as very soft and short beeps. The SPDIF output is unaffected, so I use that on an external DAC.

Last edited by jitter; 26th November 2011 at 08:25 AM.
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Old 28th November 2011, 11:35 AM   #8
marce is offline marce  United Kingdom
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Its not just the PC power supply that is noisy, (in fact SMPS's can be very very quiet, is designed correctly and not underspecified for the job), the PC its self geberates a lot of noise through such mechanisms as simalteneous switching noise. The big problem is most PC's have to be designed at a cost otherwise we wouldn't buy them, and work excellently as a PC, when inerfacing to the analogue world though some sort of isolation is best, and isolation that wont couple noise.
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