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Old 25th March 2012, 01:23 AM   #1
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Default bluetooth boombox noise problems... help!

I've poked around on this site for my problem, my apologies if this is already covered.

My boombox design starts with a cctv li-ion battery with usb and 12v output.

When I connect the bluetooth receiver (using the battery's 5v USB) and the class d amp (using the 12v), I get some major noise with digital clicks and static.

If I use a rca jack input, and only touch the internal prong to the female amp jack, leaving the outer rca shielding free from the amp, it makes the noise. If I shove it all the way on, there is no difference with the noise.

All components work properly on their own. Its only when the amp and the bluetooth are powered from the same battery.

I can only find one affordable usb powered bluetooth receiver, and only one li-ion battery with usb/12v output, so unfortunately I can't vary those. But I've tried 5 different amps, all with the same results.

Can anyone help steer me in the right direction?

parts express Stereo Bluetooth Module
Lepai 2020 amp
ebay cctv usb 12v li-ion battery


Thanks So much, Tor
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Old 25th March 2012, 02:25 AM   #2
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It's a ground loop problem. Only 2 solutions (you'll not like either)

1) run 2 separate batteries

2) add a fully insolated DC-DC for one or the other part, probably the USB device.
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Old 25th March 2012, 03:15 AM   #3
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Why won't I like the dc to dc thing? What does that entail?
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Old 25th March 2012, 09:38 AM   #4
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Quote:
Originally Posted by torclausen View Post
Why won't I like the dc to dc thing? What does that entail?
Loss of efficiency and considerable extra cost. Probably cheaper to get an extra battery than a fully isolated dc-dc converter.
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Old 26th March 2012, 07:10 PM   #5
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I'm being told I can filter it out. (no luck yet though, its very loud). I have a hard time believing that every bluetooth boombox on the market has two batteries running the amp and the bluetooth. I must be able to do it.

http://musicalfurnishings.com/diagrammm.jpg

Noise - YouTube

Tor
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Old 27th March 2012, 01:14 AM   #6
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Its strange, but I haven't seen a single homemade, diy Bluetooth boombox on the internet, yet there are numerous one sold in target, because they are amazing. I think what I am doing is very difficult.

Parts Express had nothing to offer when I called their tech.

I wished I could remedy this easily ~

Tor
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Old 27th March 2012, 05:52 AM   #7
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You can. See post #2 above. Your problem is that you're using 2 separate devices. Each with their own ground plane. When you connect these from the same battery you will have ground loops.

Had it been designed as one single unit it would natually not have the same problems.
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Old 27th March 2012, 05:05 PM   #8
gmarsh is offline gmarsh  Canada
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How about something like this:

http://www.amazon.com/Stinger-SGN20-...p_ob_e_title_2

A lot cheaper than an isolated DC/DC or extra battery.
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Old 27th March 2012, 08:54 PM   #9
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In Further thinking, how does a bluetooth car deck do it? Obviously both using the common car battery. Or a small bluetooth boombox at retail stores, one battery right?. Or quiet car 12v cigarette powered bluetooth receivers with aux out like the giffin bluetrip? Do they all have expensive dc to dc converters?
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Old 27th March 2012, 10:13 PM   #10
Eva is offline Eva  Spain
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Use either one audio 1:1 transformer or one balanced input op-amp stage per channel to break the ground loop.
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