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Old 22nd December 2011, 03:25 PM   #1
maurycy is offline maurycy  United States
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Join Date: Dec 2005
Location: NJ
Default Need help with connections (Brian's LM3875 kit)

I have posted that in Chipamp forum and got over 50 views but no replies so I am trying here.

Long story short: I am moving once completed Brian GT's Rev C LM3875 chipamp to a new case and adding second PSU board and second torroid. I had everything working with one trafo and one PSU board and since my electronics knowledge is limited, I am hoping that somebody here could take a look at the attached connections schematic and let me know if I got everything correctly or not.


Because of the CT torroid, I have only four diodes in each PSU board and I have the necessary jumpers. They are just not shown here.

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Old 22nd December 2011, 06:50 PM   #2
AndrewT is online now AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
I can't tell.
The amp diagram does not show the ground connections on the PCB.

Locating the Main Audio Ground on the PCB works for a monoblock. It does not work for a two channel amplifier.

Have a look at the RCA to pot signal return wire.
You have two of them.
Have a look at the pot to SG signal return wire.
You have two of them.
Have a look at the speaker terminal return wire.
You have two of them.
Have a look at the PSU to PG- wire.
You have two of them.
Have a look at the SG to CHG wire.
You have two of them.

Do any of these grounding connections form a loop that impresses ground current on either of the Signal Return traces on the Amplifier PCBs?

Where is your Main Audio Ground?

Do any of the high current loops form a transmitting aerial that sends radiation to any of the loops in the Signal Flow and Return loops?
regards Andrew T.
Sent from my desktop computer using a keyboard

Last edited by AndrewT; 22nd December 2011 at 06:53 PM.
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