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Joined 2002
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 can’t 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
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 can’t 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
Member
Joined 2002
Here is a picture of the psu board.
It is setup as CRC with 3.oOhm resistors @ watt each.
It is setup as CRC with 3.oOhm resistors @ watt each.
An externally hosted image should be here but it was not working when we last tested it.
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Joined 2002
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Joined 2002
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Joined 2002
And here is a link to my crappy drawing to how it is all connected.
http://jleaman.ath.cx/aleph/testing-psusm.jpg
http://jleaman.ath.cx/aleph/testing-psusm.jpg
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.
Cheers
Andrea
Cheers
Andrea
Member
Joined 2002
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 ?
That's indeed the idea.
If you want to use a shielded wire for inputs just connect the shield to one side only.
Cheers
Andrea
If you want to use a shielded wire for inputs just connect the shield to one side only.
Cheers
Andrea
Member
Joined 2002
jleaman said:
-IN should be connected to SG, but that's not creating a ground loop.
R0 should be 3R3@3W (according to A30 sch) or jumpered. 😉
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Joined 2002
Mad_K said:
I don't understand. and my other mini a's not in this chassi work 100% with out any hum only this one in a chassis.
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Joined 2002
Ok i did what you suggested MAD_K but there is still hum. It sounds like it is more lighter but less deeper now. Now to test and see if i should be shielding the interconnect cable now from the pcb to the rca jack..
So what value did you use for R0?. Also, do you use a 10R/5A thermistor from GND (on psu board) to the chassis/Protective Earth? Both of these components are used to supress ground loops.
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Joined 2002
Mad_K said:
R0 is = 3.0Ohm @ 3 watt
and i have a thermister on the ac side of the ac plug but not on the gnd i could try one there but i doubt it will do any thing. I have tried removing the ac gnd from the circuit and it does nothing.
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Joined 2002
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