Speakers picking up a lot of RFI

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dparm

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At my computer I have a pair of JBL Professional LSR2325 monitors. They sit on the desk, and the PC sits on the floor. The PC is connected to a USB DAC, which outputs the sound to the two speakers via Belden stereo-audio cables (3.5mm RCA style). The speakers are connected to the matching JBL LSR2310SP subwoofer via Belden XLR cables. In other words, all the cables are fairly-well shielded.

Over the past year I have been getting a lot of audible RFI from the speakers, typically in sync with periods of heavy activity from the PC (heavy network traffic, SSD read/writes, moving the wired mouse around, etc). It's audible as very faint and high-pitched modulating squealing and hissing.

Here's what I've done to try and fix it:

1. Switched out all cables (USB, RCA, XLR, power)
2. Replaced AC adapter on DAC
3. Moved DAC to different spot on desk
4. Re-tightened all PC motherboard/grounding screws
5. Swapped power strips
6. Moved speaker power cords to other end of power strip
7. Bypassed the DAC entirely
8. Plugged the power strip into a different outlet

I cannot get the sound to stop. It's driving me crazy.

I'm fairly convinced it's just [censored] power in my apartment building, as the APC power strip will occasionally indicate a "site wiring fault".

Any other things worth trying? Photo, for relevance:



IMG_7173_zps9e53c9f6.jpg
 
Site wiring faults are usually bad grounds I'd start there. Maybe run an extension cord to another room that has a good one?
 
Capacitors on the motherboard, Videocard or Sound card.

Bet you can hear it from the PC itself even with the speakers not connected.

Welcome to made in China.
 
To elaborate, the whole circuit/ chain you've been plugging into is the same. Run an extension cord to the one behind the washer (for testing); that is by code a single device circuit.

Also, could it be a motherboard resources glitch? Like the system bus is doing something and can't pay attention to USB for 1/100000 of a second?
 
Originally Posted By: eljefino

Also, could it be a motherboard resources glitch? Like the system bus is doing something and can't pay attention to USB for 1/100000 of a second?



Doubtful, as this identical setup did not have this issue when I lived somewhere else.

It's not that sound ISN'T being played, it's that the speakers themselves are playing back some sort of interference.
 
Originally Posted By: 123Saab
Capacitors on the motherboard, Videocard or Sound card.

Bet you can hear it from the PC itself even with the speakers not connected.

Welcome to made in China.



That would be disappointing if that's the case, as this is a fairly expensive eVGA motherboard and I've had nothing but excellent luck with them over the years. It carries a 10 year warranty, but how do you even prove the caps are flaky?
 
Stress on Caps develops over time, I still stand by what I said.

And probably even listen to your Power supply on the PC under load.
 
Add:

I had a EVGA videocard that was super loud under load, Like a whistle.

Old 6800GT.

Took it a year to develop that.
 
Sound card. I would start there. Hit the one on Ogden, you may see me in there. lol
 
Originally Posted By: Fluids
who makes your power supply?



Thermaltake. It's going on 4 years old.
 
Originally Posted By: lugNutz
Sound card. I would start there. Hit the one on Ogden, you may see me in there. lol


The USB DAC is fine -- as I stated above, the sound can be heard even when you bypass the DAC.
 
Originally Posted By: dparm
Originally Posted By: lugNutz
Sound card. I would start there. Hit the one on Ogden, you may see me in there. lol


The USB DAC is fine -- as I stated above, the sound can be heard even when you bypass the DAC.
Sorry about that. I forgot you mentioned that when I was reading everyone else's posts. I'm going to jump on your bandwagon of [censored] wiring. It sounds like it could be a ground loop issue caused by the PS, especially if you are getting the faults as you mentioned. Keep us updated!
 
It's probably your PC Power supply. I had a really really terrible quality power supply once. It had zero filtering stage and whenever I had it turned on it would cause RFI interference and buzzing on speakers plugged in.
 
Originally Posted By: Quest
if your speaker input is USB based, and you've tried snapping on ferrite clamps on your speaker's USB input cable to no avail, then your power supply filtering capacitors (or mobo part also) needs attention.

If you have a fresh new ATX power supply handy, try swapping it out and see if there's improvements?

Nice speakers BTW.

http://www.radioshack.com/product/index.jsp?productId=2103222

Q.



The USB cable going to the DAC has a ferrite suppressor built in, and I even swapped for a different cable.
 
A few Q's:

1. How old is your confuser? Are the components the same age or have you updated various parts when they needed to be?
2. If your sound card has an optical out and your external DAC has an optical in, you can use that to break any (potential) ground problems.
3. Plug headphones into the audio out jack on the sound card. Hear any noise?
4. If you own an oscilloscope, you can check for the presence of AC on the power rails.
5. Weak/poor quality/cheap PS electrolytic caps going bad, allowing noise to get through. (I had to replace a (formerly) nice Antec PS due to several bad caps).
6. Bad caps on the MB and or sound card.
7. Noisy switching transistor...
8. Poor connection somewhere....

Sounds to me like it's source related, thus internal to your machine. Do you have a LT you can swap for your DT?

#3 above will quickly tell you.
 
Can you use the speakers on another computer like a laptop to see if the problem is in your pc or in the speakers?
 
Likely you can also use something like an iPod or similar device to test the speakers as well. Doesn't have to be a laptop.

If the speakers are powered, the interference could enter via that power supply.
 
does it do it with an ipod/mp3 player type device with the computer turned off?

if so its most likely the speaker power supply.
 
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