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Old 18th January 2008, 08:43 AM   #11
digi01 is offline digi01  China
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Quote:
Originally posted by Paswa
Why need the break resistor of 6 ohm??
because when the equipments are interconnected,there are big earth loop caused by the common earth terminal on the wall IEC socket.
the 6 OHM is not a regular value.and the break resistor is not the only way.it is just simple.

Zang
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Old 18th January 2008, 08:59 AM   #12
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Quote:
Originally posted by gainphile
Thank you....thank you...

I think one of my mistake is not isolating the input RCA grounds. They are connected to the chassis!

I Had problems finding a isolated panel mount rca connector for my projects , But this really is a very most important thing.

I built a 5 channel surround amp with each channel in its own enclosure and one enclosure for my powersupply , so basically i have a small star ground in each of the 5 amplifier enclosures. Luckily i have now hum.

tang
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Old 18th January 2008, 09:46 AM   #13
AndrewT is online now AndrewT  Scotland
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Hi,
I prefer the post7 grounding layout as it gives more consistently low hum compared to post5 for two channel amplifiers.

I also find that when using multichannel amplifiers that separating the PSU grounds helps as well. This requires the use of dual rectifiers for each PSU and then connecting the zero volt line from the smoothing caps to the star ground.

Finally, there is a safety issue that has been overlooked with the layouts posted.

The 6ohm disconnecting resistor between Safety Earth (chassis) and Audio Ground (Star Ground) does not comply with the mains safety requirement of most countries.

The exposed conductive parts must be permanently connected to the Safety Earth.


The reason for this requirement is to ensure that the mains fuse blows quickly, if the mains live lead during a fault condition contacts and/or connects to other low voltage parts of the equipment.
If fault current prior to the fuse blowing passes from Live to Audio ground then through the 6ohm resistor to Safety Ground back to distribution board earth the voltage appearing on the audio ground will be high enough to kill anyone that happened to touch the equipment at the wrong time. Further, fault current passing through the resistor will more likely blow the resistor before it blows the fuse, leaving the Audio ground at Live voltage and no effective connection to Safety Earth.

I recommend either of two solutions.
The first and safest is direct connection from Safety Earth to Audio Ground. This generally gives rise to hum loops in most connected equipment.
The alternative is to use a Disconnecting Network between Audio Ground and Safety Earth. This Disconnecting Network can consist of a parallel combination of:- Power resistor, inverse parallel coupled Power diodes, Power Thermistor, HF capacitor.
The Disconnecting Network MUST survive LONGER than it takes the mains fuse to rupture and for the arc to extinguish.
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Old 11th May 2008, 06:24 AM   #14
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Quote:
Originally posted by digi01
the attached is another idea.
it is useful when you build an integrated amp with pieces single channel pcbs.
connecting all pcb's ground track via a strong wire.i use 4mm diameter copper wire.this wire is your amp's common ground.then connecting all RCA plate together to this common ground.

again,
assemblied the amp units as compact as possible.

Zang

If this grounding scheme is used, but the power supply is in a separate chassis (6 foot cable between the two), should the break resistor be put in the amplifier or power supply chassis?
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Old 11th May 2008, 08:00 AM   #15
gareth is offline gareth  Wales
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As Andrew T has stated, never put resistance onto your safety earth.

Under fault condition there will be :-

a) high AC voltage on any exposed metalwork (OUCH!)
b)your protective devices will not operate properly in the specified
time (double OUCH!!)
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Old 11th May 2008, 08:42 AM   #16
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Quote:
Originally posted by gareth
As Andrew T has stated, never put resistance onto your safety earth.

Under fault condition there will be :-

a) high AC voltage on any exposed metalwork (OUCH!)
b)your protective devices will not operate properly in the specified
time (double OUCH!!)

I would also be paralleling a capacitor/bridge rectifier to create the "disconnect network" instead of just a resistor
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Old 11th May 2008, 09:07 AM   #17
gareth is offline gareth  Wales
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Quote:
Originally posted by fluckscapacitor



I would also be paralleling a capacitor/bridge rectifier to create the "disconnect network" instead of just a resistor

What would you like to know in regards to this?

Gareth
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Old 11th May 2008, 02:36 PM   #18
jb74 is offline jb74  United States
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Thanks Digi01

Images posted here by Digi01 are excellent !!

What the (DIYaudio) world needs now is -

a translater/image maker who will -

translate AndrewT's "two solutions" in post 13
into an image as clear and easy to understand
as those posted by Digi01
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Old 11th May 2008, 05:11 PM   #19
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Quote:
Originally posted by gareth



What would you like to know in regards to this?

Gareth

The appropriate way to do star grounding (which may or may not include the disconnect network) with a stereo amplifier that has a power supply in a separate chassis and a long cable between them
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Old 11th May 2008, 08:42 PM   #20
gareth is offline gareth  Wales
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Quote:
Originally posted by fluckscapacitor



The appropriate way to do star grounding (which may or may not include the disconnect network) with a stereo amplifier that has a power supply in a separate chassis and a long cable between them

Perhaps this will help. Also pay attention to where your equipment is supplied from. I do not connect mine from different outlets and I also use a radial supply and I have never had any ground hum loops.

Gareth

PS..I think I should state again that you should not put any sort of resistance on your supply earth, you will be asking for trouble under fault conditions. Apply ohms law with some figures and see what you come up with to support this
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