fdg
Member of the Trade: Lake People
- Joined
- Oct 29, 2009
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About ground-lift and other jumpers.
Decades ago we developed our system of ground-lift jumpers.
This was based on our experiences with broadcasters and other large scale installations,
some of them more, some less professional.
If every item from all manufactures was made with a metal case and equipped with a 3-pin mains cord,
all these efforts would not be necessary. But real life is not that perfect.
Let´s begin with some words about the electrical power.
Standard AC voltage all around the world is about 115 V or (more reasonable) around 230 V.
Both these voltages are dangerous for your health if touched.
The wall outlet shows two or three connectors.
1. The dangerous one is called L = Life, the color of the associated wire is black or brown
2. The other one is called N = Neutral, the wire color is blue or white.
Those both are in charge when there is some apparatus with a 2-pin plug like small (plastic) appliances or wall plug adaptors.
Please note that with such 2-pin plugs the case of an apparatus may be unsafe when a high voltage is connected
accidentally to the case and you touch it or another item which is connected to it.
3. To make an item with a metal case absolutely safe for the user there is a third wire
called E = protective earth with the color yellow/green or only green.
In some countries the relationship between these 3 contacts is mechanically fixed so that a mains plug can only be inserted in one way.
But there are also AC outlets where the mains plug may be inserted reversed and so the relationship between N and L is also reversed.
The best way for trouble-free operation is to use exclusively items with a metal case and 3-wire mains cords.
These should be operated from one mains outlet. They should have balanced inputs and outputs and shall be interconnected with balanced cables.
As soon as there are one or more unbalanced items in the chain with unbalanced (RCA) connectors and unbalanced cables a complex system
of different earth/ground levels is formed which results in currents flowing around to compensate the different ground levels.
These currents always have the frequency of you mains voltage (50 or 60 Hz) and multiples of it.
When they are high enough you can hear them as hum or buzz, long before you can measure them !
An electronic item is not powered directly from the AC mains voltage but there is something in between to generate one or more lower DC voltages.
This may be a combination of a transformer/rectifier/capacitor/voltage regulator or a switch mode supply. The latter sounds simple but may not only generate hum or buzz but additional high frequencies.
Also the internal voltage generation will form an internal reference = ground which has not necessarily something to do with the external protective earth = yellow/green wire.
Concerning professional gear with balanced ins and outs the internal ground reference is connected most time to protective earth !
But this will lead to ground loops, hum and buzz in 90 % of all cases when “consumer” gear with unbalanced ins and outs is part of the system.
So it can be helpful to modify the protective earth / ground / case relationship in order to minimize hum and buzz.
Most Lake People and Violectric gear offer more than one option.
The most effective one is the “general – ground – lift” which cuts the interconnection between the case (protective earth) and the ground potential which was formed by the internal operating voltages.
This jumper is set to “lift” position ex works as this turned out to be the best option.
If you are facing hum or you think that something may perform better, this is the key.
The jumpers associated to the XLR connectors should be left in their default position and only be moved in really hard cases of hum and buzz.
It may be that it sounds even better after some modification but this is never due to our gear (namely a headphone amp) but maybe due to the interaction with the source.
Again:
The best way to trouble free operation is:
- one mains outlet for all items in the signal chain because the effect of earth level differences is minimized
- 3-wire mains cords with proper phase indication
- metal cases for all items in the signal chain what minimizes the chances of getting hum and buzz from the outside
- balanced ins and outs and balanced interconnection
Cheers, Fried
Decades ago we developed our system of ground-lift jumpers.
This was based on our experiences with broadcasters and other large scale installations,
some of them more, some less professional.
If every item from all manufactures was made with a metal case and equipped with a 3-pin mains cord,
all these efforts would not be necessary. But real life is not that perfect.
Let´s begin with some words about the electrical power.
Standard AC voltage all around the world is about 115 V or (more reasonable) around 230 V.
Both these voltages are dangerous for your health if touched.
The wall outlet shows two or three connectors.
1. The dangerous one is called L = Life, the color of the associated wire is black or brown
2. The other one is called N = Neutral, the wire color is blue or white.
Those both are in charge when there is some apparatus with a 2-pin plug like small (plastic) appliances or wall plug adaptors.
Please note that with such 2-pin plugs the case of an apparatus may be unsafe when a high voltage is connected
accidentally to the case and you touch it or another item which is connected to it.
3. To make an item with a metal case absolutely safe for the user there is a third wire
called E = protective earth with the color yellow/green or only green.
In some countries the relationship between these 3 contacts is mechanically fixed so that a mains plug can only be inserted in one way.
But there are also AC outlets where the mains plug may be inserted reversed and so the relationship between N and L is also reversed.
The best way for trouble-free operation is to use exclusively items with a metal case and 3-wire mains cords.
These should be operated from one mains outlet. They should have balanced inputs and outputs and shall be interconnected with balanced cables.
As soon as there are one or more unbalanced items in the chain with unbalanced (RCA) connectors and unbalanced cables a complex system
of different earth/ground levels is formed which results in currents flowing around to compensate the different ground levels.
These currents always have the frequency of you mains voltage (50 or 60 Hz) and multiples of it.
When they are high enough you can hear them as hum or buzz, long before you can measure them !
An electronic item is not powered directly from the AC mains voltage but there is something in between to generate one or more lower DC voltages.
This may be a combination of a transformer/rectifier/capacitor/voltage regulator or a switch mode supply. The latter sounds simple but may not only generate hum or buzz but additional high frequencies.
Also the internal voltage generation will form an internal reference = ground which has not necessarily something to do with the external protective earth = yellow/green wire.
Concerning professional gear with balanced ins and outs the internal ground reference is connected most time to protective earth !
But this will lead to ground loops, hum and buzz in 90 % of all cases when “consumer” gear with unbalanced ins and outs is part of the system.
So it can be helpful to modify the protective earth / ground / case relationship in order to minimize hum and buzz.
Most Lake People and Violectric gear offer more than one option.
The most effective one is the “general – ground – lift” which cuts the interconnection between the case (protective earth) and the ground potential which was formed by the internal operating voltages.
This jumper is set to “lift” position ex works as this turned out to be the best option.
If you are facing hum or you think that something may perform better, this is the key.
The jumpers associated to the XLR connectors should be left in their default position and only be moved in really hard cases of hum and buzz.
It may be that it sounds even better after some modification but this is never due to our gear (namely a headphone amp) but maybe due to the interaction with the source.
Again:
The best way to trouble free operation is:
- one mains outlet for all items in the signal chain because the effect of earth level differences is minimized
- 3-wire mains cords with proper phase indication
- metal cases for all items in the signal chain what minimizes the chances of getting hum and buzz from the outside
- balanced ins and outs and balanced interconnection
Cheers, Fried
