Saturday, 11 February 2012

webby makes a ground loop isolator

This is a follow on from my previous post in which I made a vague effort to stop my mp3 player/phone making noise when it was connected to my car radio while charging.

While the linear regulator helped reduce the noise, it was still audible.
Time for a ground loop isolator!

For the uninitiated, a ground loop is where the ground/shielding/0v connections form a loop (hence the name). In theory this wouldn't be a problem, except that devices within a ground loop usually want to be at different potentials and throw tantrums if they can't have it their way. Or something like that... See wikipedia for a real explanation.
In my case the phone, radio and charger form a loop and I end up with lots of whiney noise coming from the speakers.

To the workshop shed basement desk that I use for everything!
Step 1: order parts
2x 1:1 audio transformers

1x box (optional, but only if you like police bomb squads)

1x shielded audio cable (I used the leftovers from the previous phone bodgery)

Step 2: Tea
Tea is the most important part of engineering, closely followed by hotglue and shiny things.

Step 3: Draw really easy to interpret diagrams
This should really be the first step, but it's a really basic project.

Normal audio cable:
From carphone2
Ground loop isolator cable:
See! dead simple! From carphone2

Step 4 make it happen:
note: 2 of the 4 cores on the 4 core cable are connected to
 ground. From carphone2

Should have made the wires longer...  From carphone2
From carphone2

No more noise!
I think I'll order some longer wire for it so I can hide it under the dash a bit more at some point. There's no degradation in audio quality (none that you'd notice over the MP3 compression and weedy speakers anyway...)
All in all, I'm quite pleased with the result

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