Balanced versus unbalanced outputs - diyAudio
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Old 22nd February 2011, 04:55 AM   #1
ksporry is offline ksporry  China
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Default Balanced versus unbalanced outputs

Not sure where to post this right now, so here should be as good as any place.
Can someonbe tell me the difference between balanced and unbvalanced outputs for both sources and speaker outputs?
What are the pro's /con's and why would one pick one over another?
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Old 22nd February 2011, 05:35 AM   #2
cbdb is offline cbdb  Canada
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Non balanced outs mean a signal voltage only on the + output, the - output is grounded. A balanced output means a signal voltage on both the + and - outs with the negative out 180 deg out of phase (or negative to the + signal).

When a line level balanced input sees this it extracts the signal by subtracting the - from the +. Any noise picked up on the line between out and in will be equal on both + and - and will cancel during this subtraction. Another advantage is if one leg of you interconect goes dead you still get some signal transfer.

A balanced amp out is the same (signal voltage on both + and - outs) but for a different reason. Here its used to get 4 times the power from the same rail voltages. At full power a +/- 30 v rail amp will put about 30 volts into the speaker, if you balance the outs your getting about 60 volts to the speaker (30 on the + terminal and -30 on the - terminal)

One thing to know. Profesional balanced outs are 14dbu hotter than consumer outputs so if your using ballanced outs make sure the out level matches the input.
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Old 22nd February 2011, 06:08 AM   #3
CBS240 is offline CBS240  United States
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Hi

Remember that for a balanced output signal you are taking essentially a (rectified) full wave signal from the power rails so you will need more reservoir capacitance but fortunately of lesser voltage.

Balanced line level inputs have significant advantages as mentioned above. Some other pros of balanced output topology is the elimination of common mode distortions. Better PSRR due to at any given time signal is taken from each power rail equally. Inherently you can get twice the SR from a balanced output. Lower voltage transistors can be used. Lower Vce(ds) devices tend to have more conductance which is good because the speaker is driven by two devices in series. They tend to be cheaper too.

Some cons are that you have more complexity since you essintially have two amplifiers, although the two amps actually bias each other. Differences in phase shift from one output to the other will create distortion. This is the reason you would want to build a "balanced" input stage and VAS that are equal and common to each other, driving two seperate output stages. Bridging two SE amps is not optimal. Creating a perfect balanced signal from a SE input is not so straight forward unless you can tolerate a signal transformer (no disrespect to the valve guys, I'm sure they would loose the iron if they could), or op-amps. Op-amp phase splitters tend to deviate in phase for HF content from inverting to non-inverting circuits, not optimal IMO.


Personally I prefer balanced topology, but we audio fananics each have our own preferences and reasons.
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Last edited by CBS240; 22nd February 2011 at 06:13 AM.
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