Ground Loop

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JohnG
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#1 Ground Loop

Post by JohnG »

There is a ground loop occurring when my 845 Monoblocks are coupled together.
Each monoblock is silent, as far as my ears are concerned, when tested individually.
Removal of a earth wire from one of the power supplies plug does remove the hum noise.
I have been informed that the earth wires should be connected, and thee are a few options to resolve the issue, whilst keeping all earth wires attached.
1, try a isolation transformer.
2, make a ground lift device, as used in recording studios
3, Make the set up a balanced design.
I trust my engineers suggested methods of resolve, I don't know the merits or pitfalls of each, so would appreciate receiving some views from others who have tried to overcome such a condition using any of the above methods.
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#2 Re: Ground Loop

Post by Ant »

How are they connected together? Presumably through a preamp?
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The Stratmangler
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#3 Re: Ground Loop

Post by The Stratmangler »

Ant wrote: Mon Jun 18, 2018 9:40 pm How are they connected together? Presumably through a preamp?
It could be a ground loop issue between the pre and power amps.
The pre would be the slightly less deadly one to ground lift
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JohnG
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#4 Re: Ground Loop

Post by JohnG »

Yes it does take place when a pre amp is connected to the RCA's. I had a slagle AVC as the pre amp, so no mains lead involved.
It was first discovered coupling the two output modules with a RCA Cable.
The engineer, is not willing to advise to lift a earth wire from any component, even though a shock from pre amp may seem a low probability.
I am more interested in understanding the pro's/con's of the suggestions offered.
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Nick
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#5 Re: Ground Loop

Post by Nick »

I am with the engineer. Does the monoblocks hum if you just connect their signal ground together?

the simple solution is a isolating transformer, but not idea as its not free.
I had a slagle AVC as the pre amp
I am unsure. Do you have a AVC now, is that the pre you are using?

Is the two output grounds from the AVC connected together? If not they will be at the source I assume.

May be worth thinking about a earth lift resistor or thermistor (or back to back diodes) as a way of making a safer earth lift.
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#6 Re: Ground Loop

Post by Ant »

When I do pre's I tend not to connect all the socket earths together on one busbar and instead have the left channel separate from the right to try to avoid loops. As they eventually connect to earth via the interconnects

Also, it may sound odd, but i have found that if interconnects have 2 wires and the shield, if the shield is connected to earth at one end, reversing the interconnect can stop hum loops in some cases. I.e the plug that the shield is connected to is plugged into the power amp rather than the pre

Free to try that, sometimes it can be that simple, sometimes not.
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#7 Re: Ground Loop

Post by JohnG »

The pre amp that was connected on Sunday, is a Slagle AVC. The system did hum when this was connected.
The system hummed before this AVC was connected, when a RCA cable was connected to each monoblocks RCA Socket. This was the fly in the ointment moment.
Back to Back diodes were the first remedy used, after playing with the earth connections.
The Back to Back slides fixed the hum, but was diode dependant, the engineer expressed further remedies, of which I asked for comments in.
A 500va isolation transformer would be the minimum model, Ouch!
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Nick
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#8 Re: Ground Loop

Post by Nick »

The Back to Back slides fixed the hum, but was diode dependent
Can you explain what that means?

Maybe its worth checking just what size the leakage to earth current is?
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#9 Re: Ground Loop

Post by JohnG »

I think I had been in the Sun too long Nick.
There was two diodes placed on a red perforated block. When the crocodile clips were attached to the diodes, the hum disappeared.
This diode set up and a earth wire linking from one power supply IEC Plug to the diodes in the other power supply is the temporary fix.
As a result both power supply chassis will be earthed.
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Nick
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#10 Re: Ground Loop

Post by Nick »

Sorry, still not sure what you mean. The amp signal ground can be isolated from the chassis ground. The metalwork should always be connected to the mains earth with a nice thick cable (less than 0.1 ohm from any part of the metalwork to the IEC earth, and the cable should stand 24A for a minute).
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#11 Re: Ground Loop

Post by IslandPink »

Thanks for the tip . It would be nice to make this tweeter amp a bit safer than the 300B amp :D
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#12 Re: Ground Loop

Post by JohnG »

This is where my savvy with electronics will show, as I am not experienced in any way to explain the thought processes and methods put into place by the engineer. All I know is he tested his method on a lightbulb rig, to prove it was capable of achieving its purpose.
This method was presented as a temporary solution whilst the listed options were investigated by myself, as I would assume the engineer wanted me to satisfy myself on a proposal, as I stated at the time, I was concerned about any methods that would be put into the signal path that may degrade it.
i,e Balanced and earth lift.
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Nick
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#13 Re: Ground Loop

Post by Nick »

Earth lift is not in the signal path.
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JohnG
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#14 Re: Ground Loop

Post by JohnG »

Time to stop digging that hole, "I'll get me coat " :oops:
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Greg
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#15 Re: Ground Loop

Post by Greg »

JohnG wrote: Wed Jun 20, 2018 6:49 pm Time to stop digging that hole, "I'll get me coat " :oops:
No, wouldn’t it be better, if you are out of you depth, to introduce your engineer to Nick? I’m sure between them they will realise a solution.
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