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understanding star grounding
understanding star grounding
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Old 14th July 2014, 10:43 AM   #581
warrjon is offline warrjon  Australia
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Quote:
Originally Posted by AndrewT View Post
the Ground (Earth of Protective Earth (PE)) have NOTHING to do with Audio circuits.

The ONLY reason for adding in the PE is to stop us killing ourselves.

The signal connection whether it is the micro-volts from an FM aerial, or the mVac from a source, or the many volts from a power amplifier is ALWAYS a TWO WIRE connection.

You must know that.
Sorry you are WRONG sort of, a 2 wire connection is needed. BUT the return can be through PE. You do not need 2 wires in the signal cable.

Connect your oscilloscope scope to power (assuming you have 3 wire power) and probe a signal without connecting ground from the probe. You WILL see the same signal with or without the probe ground. The scope return is through the power.

If the signal is conected to the chassis and the Chassis of both amps is connected to PE then you DO have a path for signal through PE.

This is where the OP has a problem he has TOO MANY paths to ground and not all are terminated at the same point.
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Old 14th July 2014, 10:47 AM   #582
AndrewT is offline AndrewT  Scotland
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I say again.
PE is for SAFETY only.

All audio equipment will operate without a PE.

I work at my bench with the transformer towards on end and the isolated LV stuuf near the middle.

I have no PE during the build and testing phases.
I have an amplifier under test at the moment without a Chassis. It has no PE. It works just fine.

BUT !!!!
break one wire of a two wire connection for the Signal Route and the audio will not work.
Quote:
You do not need 2 wires in the signal cable.
This cannot work. A connection MUST allow current to flow around a route.
Break that route anywhere and the current stops. The audio stops.
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Old 14th July 2014, 11:08 AM   #583
DF96 is offline DF96  England
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Using PE as the ground return for the signal may sometimes accidentally happen at LF, but it seems perverse to deliberately do it. Why put your signal return right next to a power conductor carrying incoming noise and outgoing rectifier spikes - lots of scope for induction?
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Old 14th July 2014, 11:15 AM   #584
warrjon is offline warrjon  Australia
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Guys were are off track here the point is to help the OP.

PE can be return for signal but I never said this was ideal. In fact it causes noise.

Back to the original question.

You need to star ground the power amp. You have multiple paths to ground in your setup see pic 2.

If this was me I would connect the ground bar to the chassis and wire like in picture 1
Attached Images
File Type: jpg Signal1.jpg (154.2 KB, 335 views)
File Type: jpg Signal.jpg (178.2 KB, 338 views)
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Old 14th July 2014, 11:25 AM   #585
AndrewT is offline AndrewT  Scotland
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Warrjon,
your use of PE is confusing the issue.

The OP does not need to break his/her signal connection.
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Old 14th July 2014, 11:27 AM   #586
AndrewT is offline AndrewT  Scotland
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I repeat again
The shield of the coax is a signal return route.
It must not be broken at the RCA socket and it must not be broken at the amp PCB.

The signal connection is a two wire connection.
Both those wires must be unbroken throughout the whole route from Source to Amplifier.
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Old 14th July 2014, 03:24 PM   #587
Sagen is offline Sagen  Norway
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Hi

Tanx for the interest ( :

Im not gone use the PE, only using two wire powercable.
The signalcable is a two wire connection, signal and return connected at the amp PCB.
On the RCA, signal connected to centerpin. Return and shield connected together at RCA chassi.
Cut one wire and there will be no sound.
So what I ask is.
Must I isolate RCA?
Must I have stargrounding?
If so, the one and only chassi connection will be at the stargrounding?
Can I disconnect the cable that goes from groundrail to RCA chassi?

I have rerouted the amp GND cable to groundrail, before it was connected to the zero volt on the capicitors, this helped reduse the hum by say 25% at left canal and 50% at right canal ( listen at the speakers with zero volume ).

Frank
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Old 14th July 2014, 04:08 PM   #588
marce is offline marce  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
I repeat again
The shield of the coax is a signal return route.
It must not be broken at the RCA socket and it must not be broken at the amp PCB.

The signal connection is a two wire connection.
Both those wires must be unbroken throughout the whole route from Source to Amplifier.
I second this the coax cable must carry both the signal and its return to the amp board, the GND should go to the amp board only.
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Old 14th July 2014, 04:33 PM   #589
rayma is offline rayma  United States
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Quote:
Originally Posted by marce View Post
I second this the coax cable must carry both the signal and its return to the amp board, the GND should go to the amp board only.
Yes, this is absolutely correct.
Some shielded cables have a twisted PAIR of wires inside the shield. Probably not yours, though.
If the RCA jack is isolated from the chassis, the shield MUST be connected at both ends, unless there is a separate "ground" wire inside the shield that IS connected at both ends.
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Old 14th July 2014, 06:02 PM   #590
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by rayma View Post
.................
Some shielded cables have a twisted PAIR of wires inside the shield.....
Then not coaxial. Screened twisted pair is not a coaxial, the second wire of the twisted pair is the signal return. One would never dream of breaking that return wire.
A coaxial has only the flow wire up the geometric centre of the coax. The screen forms the signal return.
That screen connection must not get broken.
Quote:
If the RCA jack is isolated from the chassis, the shield MUST be connected at both ends, unless there is a separate "ground" wire inside the shield that IS connected at both ends.
H.Ott tells us to not use a drain wire version of a screened cable. Instead use a coax that has more copper in the screen.
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