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How to remove ground loop hum
How to remove ground loop hum
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Old 23rd June 2019, 09:02 PM   #1
mike99mac is offline mike99mac  United States
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Join Date: Nov 2015
Location: NY
Default How to remove ground loop hum

Hi, been making boomboxes for a while, but still far from an audio expert. If I can append a picture to this append, you should see a first build of a box with a Raspberry Pi (running volumio) with a "DAC hat". Good news is it basically works!he first from left is a switch which only controls a small 12V 2.1 amplifier fourth from left. Second from left is a headphone jack. In the middle is of course the RasPi. To complete the setup, the farthest right is a pot controlling the amp's bass. The output off the DAC hat above the RasPi is RCA jacks. The input to the amp is a 3.5mm jack. So I soldered a trio of RCA jacks to aux cord to three small wires soldered to the headphone jack. The bad news is there is a terrible ground loop hum. I can listen to the amp with a hum. I can turn off the amp and listen to the headphones with a hum. I then unplug the trio cable and plug in a RCA male to 3.5 mm male into the amp. The ground loop is gone. So I can listen to the boom box, but not the headphones. How to remove the ground loop and have both a boombox and headphone amp? Any help will be appreciated.
Trying to add picture - hmm, cannot seem to add jpeg, so I copy it to my Google site: RasPi boombox - Mike MacIsaac
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Old 23rd June 2019, 10:24 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by mike99mac View Post
I soldered a trio of RCA jacks to aux cord to three small wires soldered
to the headphone jack. The bad news is there is a terrible ground loop hum.
Can you post a photo of the cable?
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Old 23rd June 2019, 11:39 PM   #3
mike99mac is offline mike99mac  United States
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Join Date: Nov 2015
Location: NY
Default How to remove ground loop hum

Thanks for the quick reply.
Hmm, trying to insert images - seems the only way is to first upload to google sites - OK uploaded - here they are:

https://sites.google.com/site/mike99...e/IMG_1533.JPG
https://sites.google.com/site/mike99...e/IMG_1532.JPG

Cut an 'aux cord' in half (three wires), cut an old RCA input jacks patch cord in half (with ground as separate strands around signal wire), got three pieces of 24 AWG wire - soldered all together. Soldered three separate strands to 3.5mm jack.
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Old 24th June 2019, 12:33 AM   #4
rayma is online now rayma  United States
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Join Date: Apr 2011
Quote:
Originally Posted by mike99mac View Post
Thanks for the quick reply.
Hmm, trying to insert images - seems the only way is to first upload to google sites - OK uploaded - here they are:

https://sites.google.com/site/mike99...e/IMG_1533.JPG
https://sites.google.com/site/mike99...e/IMG_1532.JPG

Cut an 'aux cord' in half (three wires), cut an old RCA input jacks patch cord in half (with ground as separate strands around signal wire), got three pieces of 24 AWG wire - soldered all together. Soldered three separate strands to 3.5mm jack.
Could there be switched wires, hot for ground?
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Old 24th June 2019, 12:44 AM   #5
mike99mac is offline mike99mac  United States
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Join Date: Nov 2015
Location: NY
Rayma, thanks for the quick replies - will check for switched wires - will test all connections with multimeter...
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Old 24th June 2019, 01:19 AM   #6
rayma is online now rayma  United States
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Quote:
Originally Posted by mike99mac View Post
Rayma, thanks for the quick replies - will check for switched wires -
will test all connections with multimeter...
Unplug all ends of the cable when doing this.
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Old 24th June 2019, 03:47 PM   #7
mike99mac is offline mike99mac  United States
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Join Date: Nov 2015
Location: NY
I got the hum out. Rather than debug, I just cut the RCA jack to the DAC hat wire out. I then had left a wire soldered to the headphone 3.5mm jack with a 3.5mm male connector on the other side. I got a cable with RCA males on one end and 3.5mm jack male on the other and plugged the RCAs into the DAC hat. I also got a 3.5mm "Y cable" with one male and two females. All of those plugged together and let me split the signal. So less soldering and more plugs and versatility. Hopefully it doesn't degrade the audio quality.
Thanks Rayma for your help.
Now I can't control the headphone volume with Volumio, but that's a different problem )
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