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Loud Hum Coming From Main Outputs - Help Please

 
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MikeyB



Joined: 24 Jun 2020
Posts: 5
Location: Western New York, USA

PostPosted: Wed Jun 24, 2020 1:24 am    Post subject: Loud Hum Coming From Main Outputs - Help Please Reply with quote

I have owned my Krome 88 since 2015 and it has worked perfectly for me up until a few weeks ago. My wife and I have been recording worship music for our church's live stream, and a few weeks ago, I sat down to work on a new song. When I turned on the Krome and the rest of my gear, there was a very loud hum coming from the Krome whenever a cable is plugged into either main output (L/R 1/4" jacks). If I turn the volume up, the notes are clearly audible, but the humming noise is still so loud that the signal is useless. My Krome has not been out of my home office/recording "studio" in almost a year, so nothing has changed in the set up. All of the other equipment (mixer, drum machine, computer, monitors, DI for guitar/bass, etc) all appear to be working perfectly. I'm familiar with ground loops, so I added a ground lifter to the power adaptor's plug ... no difference. Since then, I have attempted to troubleshoot everything I can think of, but no luck. When I connect the Krome directly to any of my amps, the humming noise is there. I have tried different cables; I have unplugged every other electronic device in the room; I borrowed a power adaptor from another Krome (owned by our church) but it made no difference. Every other instrument (various guitars, basses, keyboards, effects) I own has been tested and is electrically "quiet" when plugged in, so I don't believe it is a wiring issue in my home.
The only way to get a clean signal from the Krome is through the headphone jack. In fact, the last couple of songs we have recorded have been been into the mixer via the headphone jack. Through headphones, my Krome sounds as good and clean as ever. Any ideas or suggestions would be greatly appreciated!
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voip
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Joined: 27 Nov 2014
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PostPosted: Wed Jun 24, 2020 8:06 am    Post subject: Reply with quote

It is curious that the headphone out is clean but the line outs aren't, since, generally speaking, the circuits for both share the same power supply and circuit ground. Is the hum a regular 60Hz hum, or is it different?
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MikeyB



Joined: 24 Jun 2020
Posts: 5
Location: Western New York, USA

PostPosted: Wed Jun 24, 2020 1:06 pm    Post subject: Reply with quote

voip wrote:
It is curious that the headphone out is clean but the line outs aren't, since, generally speaking, the circuits for both share the same power supply and circuit ground. Is the hum a regular 60Hz hum, or is it different?


Yes, it's a regular hum. My first thought was "ground loop", but I can't find the source. The hum is there whether or not the Krome is powered on, so long as there is a cable connected between the line out and the amp or mixer input, and the power supply is plugged in.
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voip
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PostPosted: Wed Jun 24, 2020 7:41 pm    Post subject: Reply with quote

Try running the Krome, mixer and amp from the same mains outlet, via a multiway extension, and keep the mains cables fairly close to each other. Avoid running the audio cables next to the mains cables, but keep them not too far away.

If the hum is still there, check that the audio cable ground is good, and the jack sockets don't show signs of being loose.

.
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Dan Stesco
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PostPosted: Sun Jun 28, 2020 8:24 pm    Post subject: Reply with quote

In certain situations (long plug or xlr-jack adapters) the soldering at the outputs may suffer and must be checked. It is possible the ground to be detached. In this situation is better to call Service.
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MikeyB



Joined: 24 Jun 2020
Posts: 5
Location: Western New York, USA

PostPosted: Thu Jul 02, 2020 1:44 am    Post subject: Reply with quote

voip wrote:
Try running the Krome, mixer and amp from the same mains outlet, via a multiway extension, and keep the mains cables fairly close to each other. Avoid running the audio cables next to the mains cables, but keep them not too far away.

If the hum is still there, check that the audio cable ground is good, and the jack sockets don't show signs of being loose.

.


I'm sorry but I dont follow everything in your suggestion, specifically "mains" cables vs. "audio" cables. But, I will take a closer look at the Jack sockets on the outputs. Thanks for your help.
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MikeyB



Joined: 24 Jun 2020
Posts: 5
Location: Western New York, USA

PostPosted: Thu Jul 02, 2020 1:46 am    Post subject: Reply with quote

Dan Stesco wrote:
In certain situations (long plug or xlr-jack adapters) the soldering at the outputs may suffer and must be checked. It is possible the ground to be detached. In this situation is better to call Service.


Thank you, Dan. I will check the output jacks. If I still can't determine the problem, my next step will be Service.
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voip
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Joined: 27 Nov 2014
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PostPosted: Thu Jul 02, 2020 10:57 am    Post subject: Reply with quote

MikeyB wrote:
voip wrote:
Try running the Krome, mixer and amp from the same mains outlet, via a multiway extension, and keep the mains cables fairly close to each other. Avoid running the audio cables next to the mains cables, but keep them not too far away.

If the hum is still there, check that the audio cable ground is good, and the jack sockets don't show signs of being loose.

.


I'm sorry but I dont follow everything in your suggestion, specifically "mains" cables vs. "audio" cables. But, I will take a closer look at the Jack sockets on the outputs. Thanks for your help.


In modern day living, there are many sources of stray electromagnetic fields, arising from things like mains distribution wiring, motors, and transformers, which will induce currents in cables in the vicinity. The fields will vary in strength around the room. Placing cables close together tends to result in similar currents being induced, by the above fields, in the ground conductors and audio cable screens, helping to reduce hum. There is much about the subject on the web. See e.g. section 4 of this link: https://sound-au.com/earthing.htm

Also: http://diyaudioprojects.com/Technical/Grounding-Shielding/

.
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