understanding star grounding

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#101
davemar73 said:
...................I've tried to scribble this in the diagram.
Click to expand...
the lower diagram is correct, but the NFB lower leg also returns to the signal ground.
I now prefer to see the signal ground taken from the RCA barrel/ground tag to the main Audio Ground (Star Ground). This seems to be more resistant to inducing hum/buzz than all the other ways I have tried.
 
#103
AndrewT said:

That describes double insulated equipment.
We do not have the expertise to design and build and test equipment to this standard.
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Designing and building double-insulated equipment is actually easier than earthed equipment. In some German forum it is highly advocated, because of that.

The handicap lies in testing. Mains voltage inside the amplifier (or any other equipment) must remain isolated from all metal parts that can be touched without the use of a tool. And it has to remain that way even during and after a defined mechanical impact, which is what DIYers usally cannot guarantee.

On the other hand, which DIYer can do the obligatory earth resistance and insulation tests to guarantee the safety of his earthed, self-made equipment? Must work carefully and hope for the best outcome.
 
#104
The Live and Neutral must both be considered as mains and treated as equally dangerous.
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I have been following this thread as this is a concern of mine as it should be for all. But I have never hooked my neutral to my chassis. For the very reason quoted above. I have had no issues with hum ever. Mind you I am no expert. I feel as though I build very solid equipment and "I" feel safe in "my" designs. There are extreme "very good to very bad" levels of design, engineering, and execution with DIY. I have personally seen some very scary wiring and chassis layouts. Lets just keep it safe and keep this thread going to educate more people. 🙂
 
#105
hello

which one is the best variant in interconection

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connect the cable shield at one end or both ends
 
#107
avyrez said:
hello

which one is the best variant in interconection

attachment.php


connect the cable shield at one end or both ends
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The best (and correct) variant is to connect the shield on both ends. Leaving the shield disconnected at one end is a means to interrupt hum loops. If you prepare cables like that
a) mark them, so you do not use them for anything else.
b) be aware that you are curing the symptoms instead of the disease.
 
#109
Anthony C Smith said:
many of the ideas in this thread appear lethal!
I went to a very good seminar by Bill whitlock od Jenson transformers at the AES in London, follow this link for the papers:
http://www.jensen-transformers.com/apps_wp.html

the second paper for students is good safe information.
regards
Click to expand...

A 2 hour audio version of the Bill Whitlock London seminar is available at:

http://www.aes.org/sections/uk/meetings/a0705.html

You will need to have a printed copy of the "2005 Generic Seminar Template" paper in front of you, just to follow along.
 
#111
AndrewT said:
Pacific,
would you care to comment?
Click to expand...

Hi, Andrew,

My post answered post #105 and its attached schematic, not #108.

Post #108 is one example, where the poster must find the best compromise whether the advantages of shielding the signal wires are bigger than the disadvantages of increasing the capacity between signal wires and ground. Or maybe the increased capacity is also an advantage, because it could accidentally create a convenient RF-filter. There is too little and too imprecise data to decide that from a distance.

Although there is a small possibility that this schematic could lead to hum. If there is a star-point for signal return on the PCB (signal ground, IN- or whatever it is called there), the potentiometer's gound wire and the RCA's ground wire should go there individually and both be connected to that point.

From the feedback circuit's point of view it is also better to connect the speaker return to the PCB's ground. That entails however sufficiently big traces one the PCB for the current involved.

Regards
David
 
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#113
Hi,
if the diodes are doing their job to pass peak and fault currents then the cap should never see more than a few volts.
I have used both ceramic 50V and MKT 100V in this location. It seems to make no audible difference and I cannot see a safety issue with using 25V here.
 
#114
A ceramic or normal film capacitor will be sufficient as long as the bridge rectifier is either working normally or internally shorted. If the unlikely event of a phase to amplifier ground short ocurrs at the same time as the even more unlikely event of an internally open-circuited bridge rectifier, the 10 Ohm resistor will go up in flames anyhow and it doesn't matter, if the capacitor does the same or not.
 
#115
pacificblue said:
....as long as the bridge rectifier is either working normally or internally shorted. If the unlikely event of a phase to amplifier ground short occurs at the same time as the even more unlikely event of an internally open-circuited bridge rectifier,........
Click to expand...
I bit the bullet and tested a similar arrangement to the ESP Disconnecting Network.
Wired the mains Live from the fused IEC socket to the network with the other side of the Network to Safety Earth.
I blew the fuse holder apart when I switched on. The majority of the glass and copper fuse disappeared with a big bang.
The Network components measured as unaffected by the Fault current and looked unaffected.
 
#116
Yes, I didn't want to give another impression. It is so unlikely that four high current diodes go open circuit at the same time, even Murphy's Law may not apply anymore.

If the rectifier is internally shorted, there is virtually no voltage across the resistor and capacitor, so any resistor and capacitor would probably live forever on that condition.

And if the rectifier is in working condition you will get 1 or 2 V across them until the fuse reacts. You could probably even get away with a 1 W resistor and a 6 V capacitor there.

A 35 A bridge rectifier usually survives several 100 A of short circuit current per diode, before it fails. This circuit is as safe as you can reasonably design one.
 
#117
#118
the first is wrong it shows the Safety Earth going to a terminal block and from the Terminal block to chassis.

The second is correct but misleading.
It shows the Safety Earth going straight to chassis but the diagram implies it could come off the terminal of the rectifier.

All exposed conductive materials must be permanently connected to Safety Earth.

Take the Safety Earth wire direct to chassis with a short robust mechanical fixture, or even welded but not soldered.

From above the permanent fixture take a connection from the Safety Earth to the Audio Ground. This can be a direct wire connection or as shown in fig2 of ESP through a Disconnecting Network.
BUT,
that connecting wire and/or Disconnecting Network must survive longer than it takes the mains fuse to rupture and for the arc to extinguish. This fault current can run to kA.
The bigger the mains fuse the longer it takes to disconnect the fault.
 
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