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Old 26th May 2010, 01:58 AM   #1
semi932 is offline semi932  United States
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Default Confusion about star grounding?

I'm trying to understand this cause I've got a hum problem trying to run two 3886 boards. One per channel with two 3886's per in bridged mode.

But my real objective is understand the star grounding to solve my own problem.

Each board can be run in stereo mode and when done singly they are fine.
Bridged mode is where the trouble begins.

I've searched a lot of threads on this subject and my concrete brain isn't very pourous.

Q's
When using two bridges with one trafo, what is the 0 volt line?

When using one bridge should the 0 volt live be connected to case?

Do the filter caps get connected at the 0 volt point to the star ground?

I've been using this pic the LM38758 layout diagram from the mimimised decibel dungeon page.

I'm new and having a hard time grasping this so all info is appreciated.

Be gentle.
Thanks
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Old 26th May 2010, 02:27 AM   #2
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When using 2 bridges, the blue line in the picture is the 0 volt line.
When using 1 bridge, if you have a center-tap transformer, connect the center-tap to the 0 volt line.

In both cases you should connect the 0 volt line to the chassis/safety earth.
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Old 26th May 2010, 03:36 AM   #3
semi932 is offline semi932  United States
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Quote:
Originally Posted by Redshift187 View Post
When using 2 bridges, the blue line in the picture is the 0 volt line.
When using 1 bridge, if you have a center-tap transformer, connect the center-tap to the 0 volt line.

In both cases you should connect the 0 volt line to the chassis/safety earth.
Thank you a lot for enlightenment.

I was really confused about the differences in bridge choices and earth grounding of O volt line.

I'm sure I'll have more questions but those answers clear my mind at this point.

Chow
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Old 26th May 2010, 07:56 PM   #4
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If you have hum after connecting like above, you can try a ground loop breaking circuit consisting of a bridge, capacitor and resistor between the safety earth and the 0 volt line.
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Old 26th May 2010, 11:02 PM   #5
infinia is offline infinia  United States
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Quote:
Originally Posted by semi932 View Post
I'm trying to understand this cause I've got a hum problem trying to run two 3886 boards. One per channel with two 3886's per in bridged mode.

Q's
When using two bridges with one trafo, what is the 0 volt line?

When using one bridge should the 0 volt live be connected to case?

Do the filter caps get connected at the 0 volt point to the star ground?
The junction of the big filter caps is usually considered ground star "heaven" for all power amps. This point is the return for the following

1) power return (from minus speaker connector and chip amp power)
2) signal ground (from amps input RCA barrel and feedback DC block cap)
3) to chassis (usually through a resistor or network) see link here

It's same star point If you have 2 bridges and one XFMR. see link
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Old 27th May 2010, 04:45 PM   #6
semi932 is offline semi932  United States
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Quote:
Originally Posted by Redshift187 View Post
If you have hum after connecting like above, you can try a ground loop breaking circuit consisting of a bridge, capacitor and resistor between the safety earth and the 0 volt line.
Thanks for your help.
I've seen that on the dungeon site.

Turns out specific problem was in one circuit board. Finally tracked it down and still have to fix it.

Take care
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Old 27th May 2010, 04:47 PM   #7
semi932 is offline semi932  United States
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Quote:
Originally Posted by infinia View Post
The junction of the big filter caps is usually considered ground star "heaven" for all power amps. This point is the return for the following

1) power return (from minus speaker connector and chip amp power)
2) signal ground (from amps input RCA barrel and feedback DC block cap)
3) to chassis (usually through a resistor or network) see link here

It's same star point If you have 2 bridges and one XFMR. see link
Good link.

There is so much info on that site.
Wish I was in need of products from him.
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