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Device for cleaning up monitoring signal
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audiodef



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PostPosted: Wed Dec 30, 2015 6:54 pm    Post subject: Device for cleaning up monitoring signal
Subject description: Is there?
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I have a pair of Mackie Onyx mixers, and JBL and KRK monitors. When I want to turn things up, there's a bit of "turn up hum". It's actually not appreciably noticeable until I turn it up to a level that's uncomfortable, but I'd like to try to eliminate it.

Is there any device I can insert between my mixer's output and my powered monitors to clean up the signal?

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DES



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PostPosted: Fri Jan 01, 2016 10:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hum can be generated in several ways...ground loops, defective gear (noisy internal power supplies or bad grounding), induced noise from transformers, light dimmers, etc. There are power isolation boxes..I believe Triplite and Monster make some...that help reduce AC line noise. Also hum eliminators for audio signals. You need to do a search for these but I think Whirlwind and maybe Radial Technologies had some. These usually work by isolating the ground betweeh audio devices using transformers.

Do you know where the hum is originating from? Best thing to do is unplug every input from the mixers and then turn up the volume to see which mixer/speaker/amp is causing the hum. Probably best to do it one set at a time...mixer to speakers. Use the same speakers and try the other mixer. Same thing but use the other speakers. Important...dont change where these are getting there power from - yet. If any of these combinations are giving you hum, try changing where they are plugged into and see if that eliminates it. If so, then don't use the offending power outlet, if possible.

If the combos above all seem good, start connecting gear, one piece at a time and raising levels till the hum returns. When it does try changing the offending gears power source and see if that helps. If not that piece may just be noisy or require service to replace components..caps, etc. Something else to take note of...cables. Always use shielded for audio and balanced if possible. Between the mixers and powered speakers this shouldn't be a problem. From keyboards, effects, etc. most likely you will be using unbalanced though a lot of rack mount effects have balanced i/o.

If you find where the hum is actually coming from then you can look into the correct fix for it. BTW laptop power supplies can cause a lot of noise...using an isolator on their power may help...

As for something between the mixers and speakers...balanced cable should do it. If not make sure the mixers and speakers are plugged into the same power outlet/strip. If you still have hum, an audio engineering trick would be to disconnect the audio cables shield at one end on each cable between the mixers and monitors. To be clear about this...take a balanced audio cable and unscrew the cover at one end. There will be three connections - two wires that go to tip and ring (or to two pins on an xlr) and the shield which is most likely braided wire. Disconnect the braided wire from the plug and either tape (yuk) or heat shrink (yea) over it so it can't touch anything. Put the cap back on and plug this end into the powered speaker. Do the same for the other cable(s). This helps to isolate the ground circuits between the mixer and speakers. The two wires that are connected still allow audio to pass.

You can use audio hum eliminators as mentioned earlier which will insert transformers in line, but it will cost a lot more the method mentioned. And, if the method doesn't work, you can reconnect the shields and try hum eliminators.

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audiodef



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PostPosted: Sat Jan 02, 2016 9:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, Dave. That's very useful advice. Smile
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egw
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PostPosted: Sat Jan 02, 2016 10:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Excellent advice Dave!
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