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Discussion Starter · #1 ·
I have been able to remove virtually all traces of interference from dScaler. First I swapped out the an old WinTV card for an ATI TV wonder. This managed to reduce the noise but the interference was still evident. I have now replaced my Quiet PC PSU with a PowerPCcooling Silent 400 and the interference is gone. One word of warning though because even though this PSU is described as ultra quiet, it's not. To get around this problem I have replaced the PSU fan with a 12db Papst fan. I'm just glad that having spent $175 on a PSU and $20 on a replacement fan that it wasn't all for nothing!
 

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All the talk about the power supply causing video interference is leading me to think that it might be worth the effort to build a set of low pass filters for the power supply lines going to the mother board.


The basic filter would be an inductor in series with the supply line and a capacitor tied to ground. The values of the components determine the resonance frequency of the filter circuit and the slope of the filter.


But first, has anyone tried this approach? I know that Ken was working some power supply magic an the individual cards, but if you can attack it at the source, that may be a better overall solution. Of course, there may still be some noise from all the other components in the computer so, perhaps it would take some filtering on the individual cards to achieve the noise reduction we are all seeking.


 

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Is there some good objective way to measure power supply noise?


Cliff and some others have done very good things putting the output of sound and graphics cards on a scope.


Is that possible for power?


- Tom


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Getting started:
HTPC Faq , dScaler , Xcel's Links .
 

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Sure,


A DC source will be a straight line on the O-Scope. If you subtract off the DC component all you will be left with is noise. This can be done using a few op-amps to make a signal comparator. Most lab O-Scopes have this type of stuff built in, so it's not a difficult thing to do in general.


Now, you can run the noise through a FFT to determine the frequency components that comprise the noise spectrum of the power supply. Many digital O-Scopes will allow you to perform some signal analysis functions on the signal, but in order to do anything really fancy it takes either a Spectrum Analyzer or standalone PC software. Once you know what's the lowest frequency you have to deal with you can then design a low pass filter that blocks most of the higher frequency noise coming from the power supply.


Of course, there may be some component of the noise that has relatively low frequency. This type of noise is hard to filter effectively using passive components.




[This message has been edited by JoeFloyd (edited 05-11-2001).]
 

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Discussion Starter · #5 ·
Before settling for the Silent 400 I was in the process looking for a medical grade PSU, then I read a review somewhere on the net that had the Enermax 550W against the Silent 400 and a number of other PSUs. The Silent 400 came out on top due to it's 'clean power' attributes. It's a pity that I had to invalidate the 5year warranty by replacing the fan.


Jeff
 

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On my previous machine I used to think I got less video noise either because I had a PC Power and Cooling Silencer 275 power supply or because I had a pretty good WinTV-d TV card.


Now I've built a new machine with another Silencer 275 in it but a different TV card and I get a lot more noise. A major step backwards.


So ... either I need a different TV card (just got another one), a bigger power supply, or it's just that individual cards and supplies vary somewhat. I don't think I have enough data points to tell at this point, even if the new modded card does help (don't know yet).


- Tom


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Getting started:
HTPC Faq , dScaler , Xcel's Links .
 
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