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Author Topic: Noise in monitors - impedance issue?  (Read 2478 times)

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Offline Ultfris101

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Noise in monitors - impedance issue?
« on: January 28, 2015, 10:53:51 AM »
I've narrowed down my problem with noise in my JBL LSR305s when using unbalanced connections to feed them. I'm way out of my depth regarding impedance and whether that's the issue or not. Looking for input on what to try to confirm that's the issue before taking next steps.

The noise I'm hearing sounds kind of like telemetry with some regular patterns of variance. Not static. I'm also not able to find input impedance data for the JBLs yet. Is that something I need to know here to sort this out? The Audioengine D1 works with both low impedance and high impedance headphones just the high impedance is a lot quieter.

Another data point: the behavior outlined in the scenarios below seems to be consistent whether I'm running through the sub or not

My goal is to use my Audioengine D1 via the RCA out if I can.

Scenario 1: balanced connection to JBLs - no noise:
  - Playback chain: PC > USB > SD USB Pre 2 > balanced XLR (500 ohms) > JBL 310subwoofer > JBL 305 monitors

Scenario 2: unbalanced RCA connection to JBLS from SD USB Pre 2 - no noise:
  - Playback chain: PC > USB > SD USB Pre2 > AUX RCA (2000 ohms) > JBL 310subwoofer via 1/4" > JBL 305

Scenario 3: unbalanced RCA connection to JBLs from Audioengine D1 - NOISE:
 - Chain: PC > USB > Audioengine D1 > RCA (45 ohm per a review online) > JBL 310 subwoofer vie 1/4" > JBL 305

Scenario 4: unbalanced 1/8" from PC to JBLs - NOISE
 - Chain: PC > 1/8" from soundcard out > JBL 310 subwoofer via 1/4" > JBL 305  (I don't have the impedance of my soundcard out handy)

Scenario 5: unbalanced 1/8" from Audioengine D1 - no noise:
 - Chain: PC > USB > Audioengine D1 > 1/8" headphone jack (10ohms) > JBL 310s via 1/4" > JBL 305

So when I go via the headphone jack in the D1 I don't get the noise. If this was simply low impedance on the D1 I'd expect that to be an issue for both the headphone jack and the RCA but they must have different properties.

Is the fact that I can go unbalanced from the USBPre2 AUX RCA outs which are 2000ohms to the JBLs without noise an indication that matching the impedance out of the D1 better should solve this?
« Last Edit: January 28, 2015, 10:58:23 AM by Ultfris101 »
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Offline schoepsnbox

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Re: Noise in monitors - impedance issue?
« Reply #1 on: January 30, 2015, 01:00:13 AM »
Sounds like a ground loop..is it a hum your hearing?  If so try lifting the ground on the gear that has a third prong with one of those adapter 3 prong to 2 and see if that helps.
Usually ground loops occur when gear is plugged into different outlets with difffering voltage potential.  If possible all gear in the chain should be plugged into the same circuit tho this is not always possible.  Hope this helps!

Offline schoepsnbox

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Re: Noise in monitors - impedance issue?
« Reply #2 on: January 31, 2015, 01:09:28 PM »
I was offering a troubleshooting input not a long term fix...I didn't see anyone else offer any suggestions.

 

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