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How to prevent amplifier from picking up interference from computer?

post #1 of 50
Thread Starter 

For a long time now I have been trying to cure the buzzing that occurs at medium-to-high volume when the amplifier is connected to my PC. This is not a hum that sounds like the typical ground loop at either 50hz or 60hz. This is an electric hissing noise with occasional clicks, and a high pitch buzz whenever I move around the mouse on the desktop. The most terrible noise comes when I launch a 3D application, such as a game. Then a loud hum appears which is very audible even when the volume knob on the amp is turned to zero; this noise only occurs when the GPU is stressed, though I can't tell if the interference radiates from the graphics card or the power supply - or both. I highly doubt it is due to the PSU since it is of high quality and power: Corsair HX1000W...

 

In any case, I was wondering if any of you have any ideas of how to remedy this issue. Thus far I have done the following to try and resolve the problem (mostly treating this as a ground loop):

 

DID NOT WORK

1. Connect all devices to the same power outlet

2. Tried higher quality + double shielded RCA interconnect from Supra, which should enhance immunity to electro-magnetic interference.

3. Muted all unused channels for the mic input (NOTE: before I started using a USB mic, I had the same irritating sound whenever I used my analog mic)

4. Chassis grounding (though I'm speculating I made errors in this part)

5. Connecting all devices to the same high quality power strip with transient filter through an ungrounded power outlet.

6. Disconnect one device at the time, in this case PC and monitor. Monitor does nothing. Disconnecting PC while turned off and RCA connected to the RCA out on sound card removes the hum (when volume on max). As soon as the PC is connected again the hum resumes, and becomes louder when PC is turned on. Same happens when connecting RCA to 3.5mm jack on mobo (onboard device). Also tried this on another PC where the buzz became significantly worse. BUT! The same thing happens with the same noise, and buzz under GPU load, when the amp is connected to the monitor (my monitor has a headphone jack + 2x USB ports).

7. (This step is mostly here to confirm it being a ground loop issue and not a faulty amp or an interference issue) While the amp is powered on for a while and connected to the PC, listen intently to the buzz/hum (very audible when GPU is stressed) and then disconnect the power cable to the amp. The amp will still be on and process sound/music until its power supply capacitors run out. All buzz instantly stopped, which confirms the ground loop occuring when more than two power connects are made to the sound system.

8. A medical grade A/C isolation transformer is generally known to be an effective way to obtain galvanic isolation/separation, but it did not work in my case.

 

WORKED

9. Tried medium priced ground loop isolator at circa $60. This worked in eliminating the ground loop buzz but perhaps at the cost of some frequencies; which is something I want to avoid. Even the more pricey option with Jensen and Lundahl transformers will degrade the audio quality to some extent, though significantly less than a cheap transformer.

10. Another thing that worked was connecting an external DAC via optical S/PDIF. Optical is generally considered the best alternative to avoid noise from interference. Haven't tried Coaxial RCA yet.

 

Will a better brand/quality of RCA interconnects help prevent the amp from picking up the noise of the computer? I had planned to upgrade my current cables for the Signal Cable Analog II for better shielding and overall quality.

 

I also tried a fairly cheap ground loop isolator-transformator which eliminated every interference noise coming from my PC and left me with a slight white noise on maximum volume only (but at the cost of some frequencies, I fear; though not that audible.) I have considered buying the Jensen CI-2RR which is a renowned transformator of high quality which should not degrade the audio signal as other cheaper devices do. I understand computers are very noisy environments and not ideal for audio in the first place, but since I am no longer using an external D/A I have to rely on my internal sound card which I so much adore. There got to be something beside an expensive transformator that can fix this.

 

Please help!


Edited by Monir - 11/29/12 at 9:10am
post #2 of 50

Is it just an amp? As in in you're connecting it straight to your soundcard via RCA?

 

If so, the sound card is the problem. I'm guessing you might be using on board audio if you're getting processor interference. But if you are indeed using a soundcard, is it pressed right up to the GPU?

 

Simply buying a 3 to 2 prong adapter for the amp should take care of any ground loop issues. Those are like 50 cents. But what you've got here is a problem with the source, not the amp.

post #3 of 50
Thread Starter 

Hi,

 

It is not on board audio but a dedicated sound card (Essence ST). And yes, it is connected via RCA. If I unplug the amp and plug my headphones into the HP out 6.3mm I have no interference noise whatsoever, even at highest volume.

 

The sound card is fairly close to the GPU also, and I can't really move it to another slot since it's a PCI card, and I only have 1x PCI slot on my motherboard. The other 4 slots are all PCI-e and I have tried moving the GPU to the slot farthest down/away with no positive results.

 

A prong adapter/cheater plug is something I would shy away from generally since I have read it involves dangerous risks going by such procedures? Also, since I live in Continental Europe I can't use 3-to-2 prong adapters since we have different power outlets. I don't know if there are any cheater plugs for European power outlets.

post #4 of 50

Hm, I've never heard it was dangerous using one of those plugs. I mean Schiit recommends them for ground loops. But yes some Googling confirms it's not exactly the safest thing to do....

 

It would be odd if you were picking up interference at all with the ST, especially if the GPU is multiple slots away. It's a shielded card. Have you tried using a headphone out to RCA adapter? Perhaps there's something wrong with the line out of the card. 

 

Also, if it was the RCA cables, you can get good double shielded cables for less than 10 bucks. Really the most important thing in interconnects is the build quality. I use GE Prograde RCA cables to connect my STX to my Asgard and I get zero interference.


Edited by chewy4 - 11/2/12 at 5:06pm
post #5 of 50
Thread Starter 

It's not just the line out. I have also tried 6.3mm - RCA cable through the HP out to the amp and I'm getting the same issue.

 

I have also tried high quality interconnects called Supra DUAL RCA 2m. Which are also double shielded and a bit more expensive, too. I borrowed them though to test; retail price is $74.

I was planning on buying the famous Signal Analog II cable http://signalcable.com/analogtwo.html but if I still have the buzz and hiss even with quality shielded interconnects I might have to invest in a transformator before I can upgrade cables. Which I want to avoid doing..

 

I could try your cables from Amazon, but I doubt they will make any difference for me. It boils down to many things, I think. One might be that you don't have a ground loop in your system, other reasons could be that my rig creates/emits more interference than your rig. I can't say much though since I don't know what components beside amplifier and source you're using.

 

Also, I won't be able to change any significant components in my rig. They were really expensive when I bought them, and I hand-picked them so that they will work best together. The mobo especially will be hard to replace since it is LGA 1366, and I won't be upgrading to, say, 2011 socket any time soon since my overclocked i7 920 will last a good while longer.


Edited by Monir - 11/2/12 at 5:37pm
post #6 of 50
Quote:
Originally Posted by boyyo View Post

It's not just the line out. I have also tried 6.3mm - RCA cable through the HP out to the amp and I'm getting the same issue.

 

I have also tried high quality interconnects called Supra DUAL RCA 2m. Which are also double shielded and a bit more expensive, too. I borrowed them though to test; retail price is $74.

I was planning on buying the famous Signal Analog II cable http://signalcable.com/analogtwo.html but if I still have the buzz and hiss even with quality shielded interconnects I might have to invest in a transformator before I can upgrade cables. Which I want to avoid doing..

 

I could try your cables from Amazon, but I doubt they will make any difference for me. It boils down to many things, I think. One might be that you don't have a ground loop in your system, other reasons could be that my rig creates/emits more interference than your rig. I can't say much though since I don't know what components beside amplifier and source you're using.

 

Also, I won't be able to change any significant components in my rig. They were really expensive when I bought them, and I hand-picked them so that they will work best together. The mobo especially will be hard to replace since it is LGA 1366, and I won't be upgrading to, say, 2011 socket any time soon since my overclocked i7 920 will last a good while longer.

You're right, trying new cables won't work if you've already tried double shielded.

 

I did have a slight ground loop(using headphone out to rca made it worse,especially with GPU running), but I'm currently using a 3 to 2 prong adapter with my amp which fixes for me. If you can find a European one for cheap I would recommend trying that first just to see if the problem is caused by a ground loop before trying more expensive options. Although I would likely say that it is a ground loop if you're not getting it when plugging directly into the ST.


Edited by chewy4 - 11/2/12 at 7:29pm
post #7 of 50

Cheater plugs can be used, though yea, they're somewhat dangerous. Proper shielding of cables is a must, but won't always be a solution.

One thing that's surely to eliminate noise would be a isolation transformer.

post #8 of 50
Thread Starter 

I could try a cheater plug, but I have to overweigh the idea of being electrocuted to DEATH and having my equipment destroyed over eliminating ground loop noise etysmile.gif

 

I also saw somewhere that the Jensen ISO-MAX CI-2RR is not recommended for some since it kills the bass? and the highs? I guess the Lundahl LL6810 cables (with built in transformers) are a viable option as well since they offer wider frequency response bandwidth; but they, too, come at a price: more expensive (since you have to buy 2x of them, about 100 euros ea) and they only make them in 2m, and for my system I need at least 3m, unless I have to move around my entire set.

post #9 of 50
Quote:
Originally Posted by boyyo View Post

 

I also saw somewhere that the Jensen ISO-MAX CI-2RR is not recommended for some since it kills the bass? and the highs? 

 

Where did you hear that? I was thinking about getting one of the Jensen's myself.

post #10 of 50
Thread Starter 
Quote:
Originally Posted by chewy4 View Post

 

Where did you hear that? I was thinking about getting one of the Jensen's myself.

http://littledot.net/forum/viewtopic.php?f=3&t=2397&sid=54e1daddd02744843549d2317a62e4d3#p7360

post #11 of 50

 

Subjective impressions should be taken with a grain of salt, especially since the transformer also makes the sound quieter (which has the psycho-acoustical effects of exactly what that forum post describes). According to the data sheet, the bass roll-off is not significant, but there is a small amount of treble roll-off (~-0.2 dB at 10 kHz, and ~-0.6 dB at 20 kHz). In any case, it hardly "kills" the highs. It should be noted, however, that due to the low and reactive input impedance, and the high output impedance, the transformer may interact with specific equipment in a way that results in further frequency response issues. There is also a some bass distortion, although it is not really significant compared to that of a typical dynamic headphone, and is probably not audible at a 2 Vrms input level.


Edited by stv014 - 11/3/12 at 9:40am
post #12 of 50

Boyyo.

As a long (long) shot.

Have disabled the motherboard's on-board audio, in the bios?

Try installing the 'Unified Xonar Drivers" from the website Brainbit.

post #13 of 50
Thread Starter 
Quote:
Originally Posted by PurpleAngel View Post

Boyyo.

As a long (long) shot.

Have disabled the motherboard's on-board audio, in the bios?

Try installing the 'Unified Xonar Drivers" from the website Brainbit.

I have had the onboard audio disabled since I purchased my sound card, and I'm also using the Unified drivers; none of which seems to help in this case.

 

Quote:
Originally Posted by stv014 View Post

 

Subjective impressions should be taken with a grain of salt, especially since the transformer also makes the sound quieter (which has the psycho-acoustical effects of exactly what that forum post describes). According to the data sheet, the bass roll-off is not significant, but there is a small amount of treble roll-off (~-0.2 dB at 10 kHz, and ~-0.6 dB at 20 kHz). In any case, it hardly "kills" the highs. It should be noted, however, that due to the low and reactive input impedance, and the high output impedance, the transformer may interact with specific equipment in a way that results in further frequency response issues. There is also a some bass distortion, although it is not really significant compared to that of a typical dynamic headphone, and is probably not audible at a 2 Vrms input level.

What would you say for the LL6810 then? I have less knowledge about transformers.

Here's the datasheet for the model: http://www.lundahl.se/pdf/6810.pdf

post #14 of 50

1) What kind of amp are you running? 

2) Do you have an open PCI-E slot? Could be worth ordering a Xonar STX and trying it. If it works, then sell your ST. STXs seem to be cheaper than STs at the moment. You might recover almost all of the cost of the STX. 

post #15 of 50
Thread Starter 

I have already tried the STX version and PCI-E does not help, plus it's a downgrade from the ST which should prevent jitter and has the upgradable 7.1 extension whenever I want to connect my 5.1 speakers for watching movies.

 

I'm using the tube amp LDMKIII.

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