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Why have an earth lift switch on a DI box?

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Why have an earth lift switch on a DI box?

Postby AndyN » Mon Oct 21, 2019 9:03 pm

I know what an earth switch does and when to use it, but why is there a switch? Why not have an earth lift as part of the circuit and leave it permanently on. Does it do anything detrimental to the sound?
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Re: Why have an earth lift switch on a DI box?

Postby Hugh Robjohns » Mon Oct 21, 2019 9:16 pm

The reason a ground-lift option is provided at all is to break a ground-loop that can exist between the mains-powered (class-1) recording equipment connected to the DI's balanced output, and a grounded amp (etc) connected to the link/thru output.

However, in a situation where a guitar is feeding an interface/mixer/recorder directly -- and there is no through (link) connection to an amp -- the guitar will need to receive a hard ground connection to minimise interference and spurious pickup of unwanted noises.

If the ground-lift was permanent, the earthy side of the guitar would 'float' and the whole instrument would act as an aerial to pickup all manner of nasties.

Although some DI boxes _do_ have a permanent arrangement intended to minimise ground-loop currents while still providing a reasonably solid ground as a convenient compromise... interference is potentially more likely.

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Re: Why have an earth lift switch on a DI box?

Postby AndyN » Mon Oct 21, 2019 9:34 pm

Amazing. Thanks Hugh for being so helpful.

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Re: Why have an earth lift switch on a DI box?

Postby Hugh Robjohns » Tue Oct 22, 2019 10:07 am

:thumbup: :D
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