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Old 9th April 2003, 07:38 AM   #1
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Default PC Power supply noise problem with sound cards - need help

I have an active PFC type power supply (Enermax 465AX-VE) which is causing electrical noise on both of my sound cards at the frequency of the mains (50 Hz) and multiples of that.

I have already tried the normal "tricks" suggested by many sites:

- move the cards furthest away from the PSU
- use an UPS (damn the good ones are acoustically noisy!)
- use grounded mains outlet (I'm running that as we speak)
- only have single ground contact (yes, always)
- shield the card with tinfoil wrapping (tried it, didn't affect
my readings)
- try another sound card (have tried RME DIGI 96/8 PAD and
Creative Audigy 2 Platinum eX, both of which some other
people have been able to make more immune to mains noise)

Is there something else I can do?

I'm sorry that I'm not an electricity guru and am at my wits end trying to solve this on my own.

I can't afford to have a separate regulated mains line installed at my home "studio" and to be honest, I don't even know if that would help.

I'd really like to hear other people's ideas on this, especially if you've tackled PC based electrical noise sources before.

best regards,
Halcyon
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Old 9th April 2003, 08:02 AM   #2
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Other than opening up the powersupply and adding some filtering of your own, i really dunno...

I once had a cd unit that was very noisy when playing audio. The solution? I built a small molex extension cable with decoupling for both the +5v and +12v rails Worked wonders! Something like that could do it, but soldering on your beloved soundcard would be insane...
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Old 9th April 2003, 08:13 AM   #3
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Default Re: PC Power supply noise problem with sound cards - need help

[QUOTE]Originally posted by halcyon
[B]I have an active PFC type power supply (Enermax 465AX-VE) which is causing electrical noise on both of my sound cards at the frequency of the mains (50 Hz) and multiples of that.

---------------------------------------------------------

I have the Enermax and have no problems. Seeing what you have tried, I wonder if the PS is faulty. Look at the ripple on the PS to assess. Otherwise why not try another PS; they are cheap compared to the sound card.
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Old 9th April 2003, 08:21 AM   #4
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Indeed. It would be pretty strange, since Enermax are supposed to be quality PSUs'. But still, it'd be cheap to try.
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Old 9th April 2003, 10:36 AM   #5
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Hi!

What is your soundcard connected to? Active Speakers or amplifier?

Try using a headphone, is the noise still there? If not, you probably have a ground loop in your chain.

Always try to use the same power line for all the components on the chain (computer, amplifier, speakers...)

If you use an amplifier, try disconnecting all other sources from the amp (when I used a normal - not DIY - integrated amp, I had two computers hooked to the amp, and as long as both were connected - even when not turned on - the running computer produced noise because of ground loops)...

I must not necessarily be the power supply....


Bye,

Arndt
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Old 9th April 2003, 02:08 PM   #6
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I need to fill in some more details, I was too sparse in my original post

The noise is not easily audible, it's still -80 dB below signal, but it is very annoying for trying to do archive quality recording for later processing, when you know that your hardware is capable of better (that's why it was bought) and that other people get 20 dB better rejection with the same sound card

I guess I will try another power supply.

Are there any special features or abilites I should be on the look for?

Like total metal casing (no fans)?

non-switched mode psu (are they even possible for PCs)?

something else?

Should I try decoupling the sound cards from the case, so that they have contact only to the motherboard and not to the casing back panel?

How about mu-metal shielding (expensive)?

regards,
Halcyon

PS It's not a ground loop. Single ground contact. However, our house wiring is old and the grounding is done via the neutral wire, so there might be potential fluctuations in the neutral wire.
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Old 9th April 2003, 06:38 PM   #7
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[QUOTE]Originally posted by halcyon
[B]I need to fill in some more details, I was too sparse in my original post

The noise is not easily audible, it's still -80 dB below signal, but it is very annoying for trying to do archive quality recording for later processing, when you know that your hardware is capable of better (that's why it was bought) and that other people get 20 dB better rejection with the same sound card

---------------------------
You should do much better. Why not do a spectral analysis of the output of your PS and compare this to your soundcard output.
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Old 9th April 2003, 06:46 PM   #8
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Hmm…

It is not necessarily your PSU. If it is digital noise, your mainboard also plays a major role. On many mainboards the low CPU voltages are taken from the +12V by switching regulators. I am using an MSI mainboard now and it generates a lot (20dB) less noise than my old Abit board with the same PSU (el cheapo Powerman).

Also take into account that mains cables generate a lot of EMI. Keep your audio cables far away from it. Preferably route them straight away along the sides of you PC. Use good screened cables.

To get some idea what the performance of your card is really is, download a program like “Audiotester”. Make a loop through cable of 10cm between input and output and see what you see. Also take some FFT’s with longer cables. You will be amazed what the influence on routing is concerning induced mains related noise.

Cheers
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Old 9th April 2003, 06:49 PM   #9
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Maybe the power supply isn't the souece of the noise. Maybe it's a grounding issue, or something? Have you tried other outlets in your house? Is the noise present with no input connected to the card?

The reason I suggest this is that it's unlikely that you would get 50Hz noise from a switch mode power supply, I think. The way they work is to rectify the mains, create a high frequency (KHz) wave, then rectify it again. It seems unlikely that the 50Hz mains frequency would make it through this process.
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Old 10th April 2003, 08:29 AM   #10
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Lightbulb Even more data

Ok, here's an RMAA 5.0 test of my sound cards non-balanced outputs to non-balanced inputs. The cable was shielded and 5 centimeters long. No mains cable nearby (I also have a very good shielded Supra mains cable).

There is nothing connected to my sound card during the testing, no amp, no speakers, no headhpones. Only the soundcard is connected to itself via the external outputs/inputs.

Of course I have KB, mouse and monitor connected. Monitor is in the same ground contact as my computer. I have tried only two outlets that I have in my room, but the results are the same.

http://www2.uiah.fi/~samu/rmaa/RME_digi_96-8_pad.html

As you can see, there's quite a peak at 50Hz and then less so at multiples of that (mains frequency).

My other sound card is slightly more immune to this noise and produces slightly better results.

Unfortunately I don't have equipment to measure my power supply noise characteristics directly (no scope).

Maybe it's not PSU noise, I'm not sure anymore. I still welcome additional ideas on how to proceed & debug.

And please forgive me if I*m a little slow on the catch up. I may not have the usual level of knowledge people in this forum seem to have

regards,
Halcyon
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