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Old 4th March 2007, 06:01 AM   #1
Arx is offline Arx  Canada
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Question 2 stars per channel, or per amp?

I'm building a 6 channel LM3875 amp

I can think of 3 alternatives for grounding. Which one is best?

1. A signal ground star per chip, and a power ground star per chip.
They're tied together at the chip.
All 6 combined grounds go to a star at the power connector.

2. A signal ground star per chip, and a power ground star per chip.
all of the signal ground stars go to a main signal ground star
all of the power ground stars go to a main power ground star
they join at the power connector.

3. One signal ground star, and one power ground star for the whole amplifier.
All of the signal grounds go to one big star
all of the power grounds go to another big star.
the two stars connect at the power connector.

-Nick
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Old 4th March 2007, 11:11 PM   #2
BWRX is offline BWRX  United States
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How will the 6 chips be powered - 1 supply for 6 chips; 2 supplies, 3 chips/supply; 3 supplies, 2 chips/supply; full mono?
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Old 4th March 2007, 11:25 PM   #3
Arx is offline Arx  Canada
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One supply,
3 pin power cable to the amp. (Ground, V+,V-)
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Old 5th March 2007, 07:34 AM   #4
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I'd say both power grounds and amp grounds all go to one star.
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Old 5th March 2007, 12:52 PM   #5
AMV8 is offline AMV8  United Kingdom
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Hi
I assume you are powering all the channels from one power source. If so my normal approach is a star ground per channel and a signal ground per channel. All channel grounds meet at a star and all signal grounds meet at a star. All connect at the power supply centre tap or ground.
Don
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Old 6th March 2007, 03:05 AM   #6
Arx is offline Arx  Canada
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Don: Sounds good. I was thinking that might be the best way to go.

My other amp I just didn't worry about it and it worked perfectly, but I think expecting the same on 6 channels would be pushing my luck.

-Nick
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Old 7th March 2007, 11:14 AM   #7
digi01 is offline digi01  China
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the physical star was set up for avoid mess unbalanced passive signal input.
one supply for 6ch is a good idea.this way is simple.
all of the signal grounds go to one big star
all of the power grounds go to another big star.
the power star connect at the power connector.the signal star connect a break resistor to the power connector.

Zang
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Old 9th March 2007, 08:49 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
in a multi-channel power amp, all the star connected grounds do not form any hum loops, as long as no ancilliary equipment is connected to any of the inputs. It is star connected by definition.

If two or more inputs are plugged in that have a common ground in the source, anywhere, then that creates a loop = hum problem.

The solution, that I see and it works for two channel, is to create an exclusive floating audio ground for each channel and use a disconnecting network to connect each channel back to safety earth.
With this arrangement all source equipment connected to the inputs will create those same loops but every loop will have the disconnecting network separating each one.
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Old 12th March 2007, 02:44 AM   #9
digi01 is offline digi01  China
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Quote:
Originally posted by AndrewT

The solution, that I see and it works for two channel, is to create an exclusive floating audio ground for each channel and use a disconnecting network to connect each channel back to safety earth.
With this arrangement all source equipment connected to the inputs will create those same loops but every loop will have the disconnecting network separating each one.

Can you draw the details?thank you advance.

Zang
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Old 12th March 2007, 03:21 AM   #10
BWRX is offline BWRX  United States
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Quote:
Originally posted by AndrewT
If two or more inputs are plugged in that have a common ground in the source, anywhere, then that creates a loop = hum problem.
That's one reason why most prefer a dual mono configuration versus an integrated stereo configuration. A differential input (like the one I used on my instrumentation configuration) will also allow you to "remotely" sense the signal ground and will not form a ground loop, regardless of the number of channels used with a single supply.
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