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Old 3rd November 2011, 04:35 PM   #1
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Default Noisy PC output

On my PC, im using the on board 6 channel sound to play music through to a stereo system.

when played through a Sony stereo, there's no noise, however, when played with my STA540 setup, I get the noise.

If I unplug the PC from the STA540 setup, the noise stops. If I plug in my Minidisk player into the STA540, it's fine so the problem is with the PC itself.

Also, I tried using a piece of wire going from one of the rings on the 3.5mm terminal to the input on the STA540 and the noise was there and thats without the ground connected.

Aside from buying a PCI 6ch card, I can't think of what else to do, any ideas?
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Old 3rd November 2011, 05:33 PM   #2
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Describe the noise. Hum? Hiss? Distortion? Also, did you build the STA540 from a kit?
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Old 3rd November 2011, 05:58 PM   #3
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see, I'm waiting on a new DSO Nano V2 from Seeed studio, if I had that I could tell you what freq it is.

It sounds like a square wave, about 1 - 2khz.

It isn't there when the computer FIRST starts up, it only starts the noise once into windows which makes me wonder whether its a driver problem.

and no, the STA540 was built from scratch including 5532 preamp, power supply, DS1802 uPots, LM3914 bar graph, Picaxe, and PWM fan speed control.

When there's nothing plugged into the STA540, it's near as damnit to being silent so the noise can only be coming from the PC
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Old 3rd November 2011, 06:13 PM   #4
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This must be a grounding problem. And most probably a new PCI soundcard could barely solve this issue.

I suppose both the PC and the STA540 amplifier have protective earth, so a ground loop is formed, which can easily lead to hum or noise.

Nevertheless, inside a PC the ground of the soundcard is connected to the housing/protective earth by a cable, which has huge currents over it (ie: cable harness between motherboard and PSU). If once the ground loop is formed, this (mainly 50Hz + switching PSU, or 'digital' -like) noise can be fed to the imput of your amplifier thru the protective grounding.

You do not have this problem with the PC+Sony stereo or in case of Minidisk+STA540, because no ground loop is formed.

There are a few soultions for this... Eg.:
-Using Loop-breaker circuit in your amp. (Earthing (Grounding) Your Hi-Fi - Tricks and Techniques)
-Connecting devices with balanced links.
-Removing PE from one device (REALLY NOT SUGGESTED because of safety)
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Old 3rd November 2011, 06:20 PM   #5
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KiKiKaKa is giving good advice. His link to the Elliott Sounds article is a good read. It could be as simple as changing where the STA540 is plugged in. Could be house wiring.
Try plugging the amp into the same outlet as the computer. Avoid outlet strips if possible.
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Old 3rd November 2011, 06:32 PM   #6
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I have had plenty of problems with noisy soundcard outputs and have found it is largely dependent on the make and model of the computer. Even though the chip that handles the sound I/O may be quite high spec, the way it is integrated may not be. This leads to output that is generally quite noisy, changing sounds as you perform different tasks on the computer and is overall quite a pain.

My experience of this has been with computers that are intended for environments where speakers will not be used-generally office PC's and business models. The sound output quality is most of the time an afterthought and no real consideration will go into the designing of the circuitry around it.

For example, the I used to have two Dell Optiplex's-office computers. Even with the computer volume on full (so none of the SNR is lost in the volume control), a pair of very inefficient speakers and the amplifier volume at a normal level, the strange sounds of the computer could still be heard. These resembled a strange background noise that was always there and ones that would appear and disappear depending on what the computer was doing (funnily enough, minimising windows and hard drive seeking seemed to make the most noise-and the latter WAS through the sound card!).

Switching to my desktop which I use daily (albeit with a different speaker system), no noise could be heard whatsoever. The internal sound card is nowhere near the best but not the worst either, and uses pretty much the same chip and codec as the other two computers (almost all Dell's use Analog Devices SoundMAX series). It is designed for home use as well as business use, so a bit more care has been taken when designing the sound I/O stages.

In most cases (as with my Dell's) it is not a case of the chip being a bad one. Most of the AD all-in-one solutions have respectable figures. Most of the time, it is down to how well this chip is integrated. Far from the input and output jacks, what components it is next to, how well filtered its power supply is etc.
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Old 3rd November 2011, 07:29 PM   #7
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Quote:
Originally Posted by kikikaka View Post
This must be a grounding problem. And most probably a new PCI soundcard could barely solve this issue.

I suppose both the PC and the STA540 amplifier have protective earth, so a ground loop is formed, which can easily lead to hum or noise.

Nevertheless, inside a PC the ground of the soundcard is connected to the housing/protective earth by a cable, which has huge currents over it (ie: cable harness between motherboard and PSU). If once the ground loop is formed, this (mainly 50Hz + switching PSU, or 'digital' -like) noise can be fed to the imput of your amplifier thru the protective grounding.

You do not have this problem with the PC+Sony stereo or in case of Minidisk+STA540, because no ground loop is formed.

There are a few soultions for this... Eg.:
-Using Loop-breaker circuit in your amp. (Earthing (Grounding) Your Hi-Fi - Tricks and Techniques)
-Connecting devices with balanced links.
-Removing PE from one device (REALLY NOT SUGGESTED because of safety)
There is no mains earth in the STA540 as it is double insulated and was built as such.

How could it be a ground loop between the STA540 and the PC when I tried with just a single wire straight from a single output channel on the PC to a single input channel on the on the STA540? There was no ground connected between the 2. That must mean that the noise is generated by the PC and perhaps the Sony stereo has some filtering circuit on the input?

The switching idea sounds plausible although I don't know what the rate of switching is, however, why does the sound only appear once the computer has loaded into windows? whilst booting it's fine.

Even when the windows jingle plays, its fine.

Got me baffled
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Old 3rd November 2011, 07:42 PM   #8
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"There is no mains earth in the STA540 as it is double insulated and was built as such."
You should have a mains earth to prevent just this problem. Try taking a wire from the ground in your little amp and connect it to the chassis of the computer.
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Old 29th November 2011, 12:09 PM   #9
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Try this,turn volume up on yor amp (not too loud !!!) if you hear a mouse movement or hard disk r/w high pich noice you may have problem wih interconection cable 3.5mm to rca stereo.I have the same noice problem with Onkiyo amp and Asus Xonar D1 and X-Fi Titanium audio card with expencive int.audio cable (3.5 to RCA jack).When I replace them with low cost cable noice just disapeard,wierd thing!
sorry for my bad engl.
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Old 29th November 2011, 12:54 PM   #10
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Sorry, I should have updated this.
I checked my power supply to the amp with a scope and its near at perfect as it can get.

I found out in the end that the noise only comes from the front jack output. When I plug it into the rear jacks, it works fine, theres no audible noise!

This in itself is fine because I have to use the rear jacks for the surround sound anyway so it's all good!!
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