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Old 30th November 2005, 06:33 AM   #1
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Default Help, bad grounding

Hi,

Excuse me if this is not the most appropriate forum for this question, I felt I had the best chance of getting some real help posting this here.

The problem is the behavior of my pre amp, which is an 1820M EMU soundcard/audiodock.

I post this here so I don't have to hear the usual "have you checked your IRQ's? Are auto updates turned off" sort of junk.

Here's my problem:

It feeds line noise through to my amp, even when muted. The amp is dead silent without the inputs from the card connected, and my cheap powered computer speakers make the same noise (though not at heart attack level) when plugged into the card.

I've experienced this same form of noise with a cheaper audigy platinum pro when plugged into a receiver before.

That's what led me to believe it was a PC SMPS issue and I recently upgraded it to a 450W Asus unit with active PFC.

These things are hardly audiophile quality, it is a sin to run such a card off of one, I'll get around to addressing that some day.

But for now...

This isn't some sort of 60Hz ground loop hum, it isn't some form of faint RFI degradation... we're talking about heart attack level CRRRRRRACKS and such, intermittantly occuring, can be very frequent or not so frequency, and which can be induced at while by turning on/off lights/fans/appliances.... the fridge is a real heart stopper.

I'm thinking it's a bad ground, living in an apartment building there's not much I can do. The computer is plugged into fairly isolated branch to the breaker panel with nothing else on it that gets used.

I don't think further line conditioning or a UPS or DC filtering the HOT lead will solve it, if the DC is seen on the ground, I'm also very unwilling and unable to try those methods..... $$$.

BTW, I have measured DC on the ground, having read an incuded 90mV on the ground outlet to the nearest water pipe with my cheap DMM just by turning a fan on and off.

So, I was considering trying a "DC filter" on the ground of the PSU for the computer, consisting of nothing more than a few 6amp power rectifiers and a small value non polar cap, possibly consisting of two electrolytics in series (both negatives connected). Something like 4700uF and 25V each perhaps?

The questions are:

1. Do you think I'm target with the cause of this evil problem?
2. Do you think my intended cure is worthwhile trying on a PC? This isn't for the amp.
3. Do you think this is safe to try with a computer SMPS?
4. Any other advice or tree's I should be barking up?
5. Do you want to buy an 1820M? .... just kidding there, but if I can't solve this I have to dump the card and find an alternative with balanced outputs that I can't afford either.

I'd greatly appreciate any sound advice on this one, and hope I've described the problem adequatly.

Regards,

Chris
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Old 30th November 2005, 07:02 AM   #2
Nordic is offline Nordic  South Africa
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Funny you should mention these cracks, since I got larger Logitech speakers, I also notice this switching noise occuring every now and again... not very often, maye once every 2 hours or so, or maybe I just tune half of it out allready...
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Old 30th November 2005, 07:16 AM   #3
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Quote:
Originally posted by Nordic
Funny you should mention these cracks, since I got larger Logitech speakers, I also notice this switching noise occuring every now and again... not very often, maye once every 2 hours or so, or maybe I just tune half of it out allready...
Have you checked your IRQ's? No just kidding.

Seriously, when it's plugged into my power amp it's impossible for the neighbores to miss, but my cheapo powered PC speakers do the same, you just have to listen for it a bit.

Being line or as I'm assuming ground noise it is completly intermittent, it can seem every few hours for one day, every ten minutes for another, usually more randomly occuring. Sometimes I tried a small tweak to a PC setting and thought it was cured for an entire afternoon until later that night... CRACK..... CRACKLE.... POP..... ZZZZZZZZZZZT.

It can be dead silent for a whole day except for when my fridge turns on/off. Depends how hungry everyone else in the building is I guess or if they're doing laundry.

This is a problem there's just no ignoring for me, and asking anywhere else is only getting me babytalk where their solutions are the typical "buy this, buy that, disable your screensaver" .. It's at the point where I might be the one doing the cracking and snapping and not even know it

There's got to be others with this problem too!

Regards,
Chris
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Old 30th November 2005, 07:39 AM   #4
sangram is offline sangram  India
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It's pretty obvious it's a line issue and not related to only your hardware.

I would try an isolation transformer with some RF-level filtering on the secondary for your problem. I don't think a UPS will solve it as it normally connects directly to the mains when the mains is present.

You can't rewire? Sometimes it'll be an intermittent contact in one joint in the chain, that arcs when load is pulled.

I would just DIY a couple of mains extensions with mains-rated cable, and bring up a fresh line form the distribution block or the nearest known good switchboard and see if that helps.
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Old 30th November 2005, 07:46 AM   #5
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Quote:
Originally posted by sangram
It's pretty obvious it's a line issue and not related to only your hardware.

I would try an isolation transformer with some RF-level filtering on the secondary for your problem. I don't think a UPS will solve it as it normally connects directly to the mains when the mains is present.

You can't rewire? Sometimes it'll be an intermittent contact in one joint in the chain, that arcs when load is pulled.

I would just DIY a couple of mains extensions with mains-rated cable, and bring up a fresh line form the distribution block or the nearest known good switchboard and see if that helps.

Right on, I agree it's something to do with the mains, and thanks, that's the kind of thinking I was after.

Rewiring is absolutely out of the question.... I rent this place, bad enough I painted it for free.

I've been able to induce 90mV on the ground, measuring from the ground of a GFI outlet to a nearby water tap, just by turning a fan on and off. I've got myself all but convinced it's bad grounding, which I can't fix at the source.

So I'm looking for the most effective and cheap bandaid that will solve this.. and so I arrived at "lifting" the ground with a DC filter for the computer. I dont' know how good that would be for the SMPS of the PC though.

BTW I've plugged the PC into a different branch.... same junk.

Regards,
Chris
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Old 30th November 2005, 09:04 AM   #6
sangram is offline sangram  India
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What's the configuration of the PC? Any special cards etc. connected except for the 1820 (seeing you had the same issue before).

I do get a little pop from the starting of my fridge from all my audio stuff, so I don't think much of it. No bad buzz like yours. Fridges dump a lot of trash on a line.

I don't think you should attempt any funny stuff at the input of your SMPS. I still think isolation is the key. If you're having problems all over your house (old wiring?) then a nice 1KVA isolator will do the trick for you.
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Old 30th November 2005, 09:28 AM   #7
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No No No!

Let's stick with the assumption it's not my computer, we were on the right track, honestly I dont' even want to humor that anymore.

For the cure you just recommended, it may as well have been to build my own generator outside. The buck stops at the new power supply.

I promise this is one time audioland is going to see a $5 cure, or less! If not I dump this card right along with the idea of ever having a soundcard as the source of an audiophile system.

Cheers,
Chris
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Old 30th November 2005, 09:52 AM   #8
sangram is offline sangram  India
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dibs on your 1820 then.

If you plan to sell it mail me using the button below.

My Delta 66 has no problem at all, even using a generic off-the-shelf-supply.

If you want a tip, try using a PSU from a PSU maker. Like PC Power & Cooling, Fortron/Sparkle etc. (Not Asus, Antec or OCZ, those are all rebranded).
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Old 30th November 2005, 12:28 PM   #9
ilimzn is offline ilimzn  Croatia
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Your problem is actually quite simple - the PC chasis is connected to the earth return, which also (indirectly) makes the card output grounds connected to it (this is actually incredibly stupid but now that it's a standard, what is done, is done). It is sufficient to connect it to any device that has no earth (but derives it's own local shielding using a capacitive difider from L and N, this is very typical!) to create a ground current. It will be low for 50/60Hz mains frequency (hence hum) but higher (much higher!) for switching transients because the ground return impedance, being inductive, is much larger for a step transient (because it is full of HF harmonics). You can also get a LOT of hum if you have two earth returns connected to the system somewhere, that come from very different points in the power grid (typically this will happen iof you gave a cable box connected to your audio system or the PC).
You should be able to solve your problem in one of two ways:
1) Isolation transformer for the PC, and you also need to lift the earth line for the PC. In theory, the latter should be enough but I would be weary of losing the protection! You may, however, have a problem with the isolation transformer - a PC's switching power supply, unless it's a power factor corrected one, creates a very non-sinusoidal current, which means you get a lot of transformer losses - so your isolation transformer would have to be overdimensioned considerably (VA rating double or more of the PC PSU W rating).
2) Use interstage/isolation audio transformers on the audio lines!
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Old 30th November 2005, 12:31 PM   #10
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Assuming that the PC system is consistent in itself, meaning that the PC card outputs - referred to the PC ground - might be error-free, did you try to lift the ground on the power amp? You MAY be creating a ground loop from the PC ground through the power amp ground. Try also to plug the power amp in the same outlet as the PC, trying to rotate one plug 180degrees to find the best solution.

Jan Didden
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