Balanced or unbalanced circuit ?

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#2
I think technically its an attempt to provide the same impedance on both output terminals. Can't think of a single reason why this would be desirable unless the receiving end was a balanced input. In which case its normal practice in audio to use XLR connectors, not jacks and provide a connection to chassis with XLR pin1.
 
#3
abraxalito said:
I think technically its an attempt to provide the same impedance on both output terminals. Can't think of a single reason why this would be desirable unless the receiving end was a balanced input. In which case its normal practice in audio to use XLR connectors, not jacks and provide a connection to chassis with XLR pin1.
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I was testing the output of my soundcard on the scope and there is no signal at all on the cold pins of the outputs... and thinking that my interface was out of order.

We should be very carefull when buying a balanced output interface...! if we really need a true balanced output ? no ? :scratch:
 
#4
Balancing doesn't refer to a requirement to have two signals of opposite polarity on the wires, rather a balancing of the impedances so that interference gets picked up equally on both conductors.

We should be careful to only connect balanced outputs to balanced inputs.
 
#5
abraxalito said:
Balancing doesn't refer to a requirement to have two signals of opposite polarity on the wires, rather a balancing of the impedances so that interference gets picked up equally on both conductors.

We should be careful to only connect balanced outputs to balanced inputs.
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Thanks for your explanations.
The "two signals of opposite polarity" configuration should have a far better noise rejection? no?
 
#9
silverprout said:
Hello,
These outputs seems unbalanced to me...
Could you say what is the technical interest of this topology ? (balanced output mark on the device)
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your circuit sch shows a balanced impedance input and a balanced impedance output.
Ideal for connecting to other balanced impedance IN/OUT with balanced cabling.
And brings with it the interference attenuation when the impedances are accurately balanced.
see Jensen ap note 3 for the circuit suggested as better than many other ways of sourcing a signal.
BTW,
B.Putzeys adopted this version of balanced impedance output for this balanced impedance volume control.

TRS is often adopted on pro stage gear as the balanced impedance connector.
There are dual purpose sockets that accept either TRS, or XLR, specially to be more universal.
 
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#11
silverprout said:
Ok, more signal for the same noise level gives a better SNR.
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abraxalito said:
That's a more succinct way of putting it, yes 🙂
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Not necessarily.
Balanced impedance inputs often have a poorer noise performance compared to unbalanced.
One can compensate for that by increasiing the differential signal, if that increase does not increase the noise on the signal significantly.

But when it comes interference noise to signal ratios, then balanced does give a big benefit, particularly when the pro levels are used differentially in a very (interference) noisy environment.
 
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