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jleaman 28th April 2006 03:33 AM

Ground Loop problem
Can any one suggest me some ideas / techniques for making some ground loops disappear. I have a stereo mon-block that a friend has built. It is a class a Mini a Both channels share a single CRC psu with a 300Va transformer. I have tried every thing I could possibly think of. When I connect a audio source via RCA it has a hum a low hum possible a ac ground.

I have connected my ipod to see if it was the source but it was not because I have tried many sources. IF I unplug one channel left/right input the hum goes away and it is dead quiet. I have tested the ac ripple on the dc psu and there is ripple there but my mini as that I have have the same amount of ac ripple on it. I seriously cant think of any thing to do with this thing any more.. I have access to a scope. Can any one suggest any ideas ? I can post pics if needed.

Things I have tried

Replaced the input rca jacks
Twisted cables for rca and speaker terminal
Put a copper piece of metal around the transformer
Put a thermister on the ac input ground

Mad_K 28th April 2006 07:05 AM

Post that pic, also it might be a good idea to draw a gound map ;)

jleaman 28th April 2006 07:20 AM

Here is a picture of the psu board.

It is setup as CRC with 3.oOhm resistors @ watt each.

jleaman 28th April 2006 07:26 AM

2 Attachment(s)
Here is a pic of the amp inside. I have the rca's mounted directly to the amplifier like how i had mine.. I still get the ground loop problem.

jleaman 28th April 2006 07:30 AM

2 Attachment(s)
Here is the amplifier board. It only has 2 fets on the output stage.

jleaman 28th April 2006 07:43 AM

And here is a link to my crappy drawing to how it is all connected.

Andypairo 28th April 2006 07:53 AM

In my (former) Aleph30 all the gnds (input and output) are taken from a star point at the power supply. This star point is connected with a single wire to the gnd of the boards.



jleaman 28th April 2006 07:59 AM

So, All the input and speaker grounds go to the same point ? Right where the dc is connected on the ps going to the main amplifier boards ?

Andypairo 28th April 2006 08:10 AM

That's indeed the idea.

If you want to use a shielded wire for inputs just connect the shield to one side only.



Mad_K 28th April 2006 09:40 AM

Are you using R0? What value?

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