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Old 16th February 2010, 12:32 AM   #1
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Default Alternative method of a loop breaker - Will I kill myself?

My power amplifier's PSU is very quite after my recent upgrade and rewiring, as shown by my oscillioscope.

A loop breaker is used, the circuit of which was taken from Rod Elliot's side : Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

However, there are mains noise as well as some other junks of up to 1.5mV ripples when measured between the lifted HQG (i.e. star ground) and the earthed chassis. As a result, some noise of 1.5mV is measured at the output. When I bypassed the loop breaker with a wire, I still measured the ripples between the HQG and the chassis. The magnitude was only slightly reduced. The 14 gauge wire connecting the HQG to the chassis / earthing point is about 20cm, but the voltage noise developed between these two points was a bit of surprise to me.

I think the chassis potential must be the same as the HQG otherwise it defects the purpose of the screeening effect of chassis. In other words, I think the best is to connect the HQG directly on the chassis. This should eliminate the potential between the circuit ground and the chassis. Somehow going through a resistor || capacitor, or even a wire still generates some potential.

The question is, if I want to retain the loop breaker to reduce the mains noise within the audio bandwidth, can I connect the incoming earth line to one end of the loop breaker without connecting to the chassis, while on the other end of the loop breaker connects to the chassis at the HQG point? In other words, the mains earth is not directly connected to the chassis but via the loop breaker, while the circuit ground is connected directly to the chassis. Would there be safety issue there? I have something to learn here.

Best regards,
Bill

P.S. The attached picture describes it better.
Attached Images
File Type: gif loopbreaker.gif (22.1 KB, 476 views)

Last edited by HiFiNutNut; 16th February 2010 at 12:34 AM.
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Old 16th February 2010, 01:38 AM   #2
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Quote:
Originally Posted by HiFiNutNut View Post
My power amplifier's PSU is very quite after my recent upgrade and rewiring, as shown by my oscillioscope.

A loop breaker is used, the circuit of which was taken from Rod Elliot's side : Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

However, there are mains noise as well as some other junks of up to 1.5mV ripples when measured between the lifted HQG (i.e. star ground) and the earthed chassis. As a result, some noise of 1.5mV is measured at the output. When I bypassed the loop breaker with a wire, I still measured the ripples between the HQG and the chassis. The magnitude was only slightly reduced. The 14 gauge wire connecting the HQG to the chassis / earthing point is about 20cm, but the voltage noise developed between these two points was a bit of surprise to me.

I think the chassis potential must be the same as the HQG otherwise it defects the purpose of the screeening effect of chassis. In other words, I think the best is to connect the HQG directly on the chassis. This should eliminate the potential between the circuit ground and the chassis. Somehow going through a resistor || capacitor, or even a wire still generates some potential.

The question is, if I want to retain the loop breaker to reduce the mains noise within the audio bandwidth, can I connect the incoming earth line to one end of the loop breaker without connecting to the chassis, while on the other end of the loop breaker connects to the chassis at the HQG point? In other words, the mains earth is not directly connected to the chassis but via the loop breaker, while the circuit ground is connected directly to the chassis. Would there be safety issue there? I have something to learn here.

Best regards,
Bill
The main earth is not directly connected to the chassis?
Well I am not an expert here but I would never leave the main earth be "Floating" like that. Make sure your outlets are grounded well, I have seen many outlets that are not properly grounded and also I have seen wires inverted like this Black = cold and White = hot. ( This is in the USA).
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Old 16th February 2010, 05:01 AM   #3
CBS240 is offline CBS240  United States
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I have seen wires inverted like this Black = cold and White = hot. ( This is in the USA).
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Old 16th February 2010, 05:02 AM   #4
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Well, many people reported much cleaner sound without earthing the chassis. Of course, we don't want to put our lifes at risk.

I am just wondering if it is workable and safe to connect the earth wire in series to the bridge (connection as per Rod Elliot's circuit but without the resistor and the capacitor) then to the chassis. In that case, there is a complete isolation of the chassis and earth, until 0.6 / 2 = 0.3V developed between them, then the bridge conducts and dumps the currents from the chassis to earth, triggering the safety switch. Wouldn't this be safe?

In that case, the chassis will never be more than 0.3V to the earth, and the PSU common can be directly connected to the chassis, achieving the best shielding effect of the chassis. No dirts coming from the earth to the chassis unless a fault is developed.

The difference between this and Rod Elliot's is that, with this the bridge is to isolate the earth from the chassis, but still provides a short circuit when a fault develops, With Rod's it is to isolate the power supply common / HQG from the earthed chassis.

I most certainly trust Rod Elliot. So the question is, what is wrong with my proposed connection?
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Old 16th February 2010, 05:18 AM   #5
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Originally Posted by CBS240 View Post
I put the same face when I saw this mess. and the bad thin is I keep seen it every now and then. I even found cheap extension cord between the walls the ones that you buy at 99c stores!
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Old 17th February 2010, 12:42 AM   #6
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Any advice? Please
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Old 17th February 2010, 12:49 AM   #7
AndrewT is offline AndrewT  Scotland
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test it.

Attach a direct short from Live to HQG.
Stand back and switch on.
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Old 17th February 2010, 12:59 AM   #8
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Andrew,

Thanks for jumping in.

Good advice. But before I go through that, I am hoping someone can verify if the scheme works or not, as I am worry about the "antenna" effect of not earthing the chassis.

I heard that these days many amplifiers coming out of China are unearthed. Obviously I don't like that because there is a safety issue. My circuit would be the same as "unearthed", but provides safety, I hope. I am just wondering if those Chinease amplifiers indeed work then there should be no such "antenna" effect that I am worry about.

Regards,
Bill
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Old 17th February 2010, 01:57 AM   #9
faiyaza is offline faiyaza  United States
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Originally Posted by HiFiNutNut View Post
I heard that these days many amplifiers coming out of China are unearthed. Obviously I don't like that because there is a safety issue.
China?! My quintessentially American Conrad Johnson Sonographe SA-250 is unearthed.

Grounding is preferred and obviously safer than the alternative. But not every appliance you plug in has it.
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Old 17th February 2010, 01:58 AM   #10
faiyaza is offline faiyaza  United States
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Originally Posted by faiyaza View Post
Grounding is preferred and obviously safer than the alternative. But not every appliance you plug in has it.
That said, now my paranoia has kicked in. How worried should I be?

I've always thought about dremeling out a hole, ripping out the stock wire, installing an EIC plug, and properly grounding the chassis.

Overkill?
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