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ground loop problem

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omri

New Member
hello,
i am building a portable music speaker that has two main components:12v audio amp and 12v radio/BT/line-in module. they both get the power from the same supplier (can be 12v battery or 220v to 12v ac adapter). when i powered it i heard a buzz and when switching to BT mode i heared a buzz and periodic beeps that changed when connected/not connected/played music.
when they get power from 2 different sources everything works fine.
i also found out the when i disconnect the (-) power from the radio module it keeps running! or when i disconnect the (-) from the audio signal it still playes music without any decrease in sound quality or volume.
after searching the internet i learned that its called ground loop. i baught a passive filter that seats on the audio signal between the module and the amp and that didnt help at all.
i need your help on this, how can i overcome that serious ground loop?
omri
 

JimB

Super Moderator
Most Helpful Member
Quick question, what is a BT ?

JimB
 

audioguru

Well-Known Member
Most Helpful Member
If the radio module has a single positive supply and ground as its negative supply then the ground is for power and for audio signal. If you disconnect the power ground then the audio ground will power it.
hum or buzzing could be caused by stray pickup by unshielded audio cables. Use shielded audio cables.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Quick question, what is a BT ?

JimB
Presumably BlueTooth?.

However, as far as the OP's problem goes he really needs to post a picture of how he's built it - as the answer might be obvious then - but a simple answer is usually to disconnect the screen from one end of the connecting wire between source and amplifier.

I've no idea where he got the idea of a 'passive filter' from, it wouldn't help a ground loop in any way - a classic way would be to use an isolation transformer (but removing one screen is simpler and cheaper :D)
 

dr pepper

Well-Known Member
Most Helpful Member
Connect the ground wire from each module to one point and at that point connect your power supply ground, also put the blutooth module away from the rest of the kit by 12" or more if you can, also the cables leading to the rf module you could salvage a ferrite from an old vga cable or computer cable and wrap the supply and audio cable around it a couple of times.

It sounds like some of the noises you hear are rf bleeding over into the audio, liek when you put a mobile phone near a radio receiver, the amplifier would filter out the rf but you'd still hear noises as the rf usually has some audio content from the modulated carrier.

On publicperformance equipment it was, maybe still is popular to put a resistor in the ground line from the audio source, but this osnt something to try unless you really know what the problem is.
 

omri

New Member
hi guys,
this how it all looks, pretty tight.
IMG_3868.JPG
when i said passive filter i meant it has no power supply.
as you can see all the grounds are connected together.
i tried to take the componnents away from eachother-didnt help.
when i connected the RF module to my aux input in my car and powered by the car's battery it made the same noise.
what about that resistor option, what should i do?
 

dr pepper

Well-Known Member
Most Helpful Member
I see theres a transformer isolator on the input to your amp, the resistor solution no longer applies if thats the case.
 

omri

New Member
the transformer isolator is what i called passive filter. i added it as a solution to the ground loop problem but it didnt help at all. what is your best offer to overcome this issue? i can take it out if needed. as i said it had no influence on the ground loop.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
My cooments are:
The audio connections should be shielded.
it would be Best, if they were shielded at one end only.

Sometimes loops can be broken, if a small resistor like 2.2 ohms is used for the music input ground side.

You really need to post a diagram of your connections and what devices you used.

Loops, generally means if you break the loop, the noise goes away. Breaking what connection causes the noise to disappear?
So, you did say that with two supplies, it works. So, is it possible to use a small isolated switching converter to power the BT module?

The rules are:
Use shielded cable for audio.
The best would be twisted pair shieleded with a differential line driver/receiver, but that won't happen. That like the XLR system for professional audio.
Single return line.
Shields at one end only. If you need the audio return then use a 2.2 ohm resistor to your star point for the audio return.
 
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