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Post subject: XLR outputs on my amp (Mustang III, V2).
Posted: Wed Sep 25, 2013 4:51 pm
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I've never had an amp with XLR connections. As a noob with this type of connector (I understand they are used to input into a mixer/recorder). Other than that, I have no Idea how the connections are used and with what type of equipment. Anyone care to elucidate on the use of XLR connectors (and the "ground lift" switch) in layman's terms ? Thanks. Hardware suggestions ?


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Post subject: Re: XLR outputs on my amp (Mustang III, V2).
Posted: Wed Sep 25, 2013 7:24 pm
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XLR connectors tend to be used where a balanced signal is needed. Balanced means that there is a ground connection, a hot signal (+) on one conductor and a reverse phase hot signal (-) on the third conductor.

The advantage of balanced connections is an effect called Common Mode Rejection. By using a differential amplifier (i.e. amplifying the DIFFERENCE between the + and - signals) you cancel out a lot of the noise that is common to the two signals.

Here's a really simple explanation:

One wire carries signal plus noise

One wire carries inverted signal plus noise

Subtract one signal from the other and you get (signal minus (-signal)) = 2 x signal

But both conductors carry the same (or similar) noise so subtraction gives you (noise minus noise) = no noise

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Post subject: Re: XLR outputs on my amp (Mustang III, V2).
Posted: Wed Sep 25, 2013 7:28 pm
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Ground lift is useful to avoid ground loops. Tube amps are especially sensitive to having more than one signal ground in the circuit and can generate hum.

As an example, running an effect processor in an effects loop can result in the signal being grounded both in the amp and in the processor. If the two ground points are at slightly different potentials (voltages) then the amp will hum until you lift one of the grounds.

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