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Understanding Balanced Audio (video)

DonH56

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#41
I have not seen the video. Random thoughts:

Balanced vs. differential is always an interesting subject in the audio world. Balanced circuits are usually differential but not always, and there is a range of differential circuits from fully-differential to quasi-differential to essentially impedance-balanced designs that aren't really differential at all in the sense I use the term. YMMV.

Ideal differential circuits cancel even-order harmonic distortion and provide common-mode rejection. The amount of improvement is very dependent upon the circuit and application (grounding one side of a differential signal tosses almost all the benefits).

With differential circuits, or bridged amplifiers (not necessarily the same thing), the signal voltage is doubled since you have two amplifiers swinging the signal with one output inverted. Assuming the noise is not correlated (normal assumption, again not always true), it does not double since the noise is not always "in phase" like the signals, so noise increase by roughly sqrt(2). The net gain is 6 dB in voltage and only 3 dB in noise, a 3 dB increase (improvement) in SNR. Plus whatever improvement you get from reducing even-order harmonics and reducing common-mode noise.

HTH - Don
 

Speedskater

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#42
Balanced circuits are usually differential but not always, and there is a range of differential circuits from fully-differential to quasi-differential to essentially impedance-balanced designs that aren't really differential at all in the sense I use the term. YMMV.
While I have a very different viewpoint, at least in regards to interconnect systems and measurement systems.
I see balanced interconnects as a sub-set of differential interconnects. Where balanced is symmetrical about a reference, but differential does not need to be symmetrical.
With three types of common balanced output stages:
  • transformer
  • impedance/passive
  • active/powered
 
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#43
@amirm , many thanks, great video as always!

You referred to balanced out on a headphone amp as being only more powerful in the video. Is that really the case, or would a balanced output also be expected to change the sound characteristics as well? I recently switched to a balanced cable for one of my favorite headphones on a Topping A50s, resulting in a significant change to the sound signature of the headphones (in a much better way), in addition to the power gain. Am I totally dreaming?
 

DonH56

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#44
While I have a very different viewpoint, at least in regards to interconnect systems and measurement systems.
I see balanced interconnects as a sub-set of differential interconnects. Where balanced is symmetrical about a reference, but differential does not need to be symmetrical.
With three types of common balanced output stages:
  • transformer
  • impedance/passive
  • active/powered
For me, and perhaps nobody else, the reference for a differential stage is the common-mode point. Terminology varies, natch. If it is not symmetric about the common-mode point then it introduces a common-mode component to the signal, usually undesirable.

Again to me (only), a transformer or active differential circuit is differential, or can be, whilst simple passive impedance matching (e.g. using resistors so the ground and signal lines have the same impedance) is not differential. No signal inversion occurs, though it can be argued that the return ("ground") line is by nature complementary to the signal line and thus differential in a sense.

Semantics was never my strong point; I be a hairy-knuckled engineer, not a high-falutin' theorist...
 

MRC01

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#45
... Again to me (only), a transformer or active differential circuit is differential, or can be, whilst simple passive impedance matching (e.g. using resistors so the ground and signal lines have the same impedance) is not differential. ...
I think of it the same way. The term balanced, as used by audiophiles, typically refers to differentially signalled + and - wires with a separate ground wire.

Put differently, as a litmus test: what happens if you ground the audio (-) wire? In an unbalanced system, nothing happens; it is already a ground, it doesn't carry a signal, there is no amp driving it. In a balanced system, that (-) wire carries an audio signal and grounding it shorts (and potentially damages) the amp driving it.
 
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#46
Put differently, as a litmus test: what happens if you ground the audio (-) wire? In an unbalanced system, nothing happens; it is already a ground, it doesn't carry a signal, there is no amp driving it. In a balanced system, that (-) wire carries an audio signal and grounding it shorts (and potentially damages) the amp driving it.
The majority of balanced connection these days are electronically balanced (as opposed to transformer-balanced.) You are absolutely correct -- things could get damaged if the cold/negative is shorted to ground, although this is only true in the case of electronically-balanced output that has no circuit to sense and adapt when the cold pin is not connected or is shorted to ground. Luckily the majority of balanced outputs (at least on pro equipment) have such mechanism. One can plug in balanced or unbalanced, or use balanced to unbalanced adapter cables, and it'll work just fine, even the output level will be adjusted automatically.

I don't know about "purist" audiophile equipment though -- having such circuit likely adds noise, so they may not incorporate it. It's best not to short either signal pins in a balanced connection. Also good practice to test new XLR cables for shorts.
 
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amirm

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Thread Starter #47
@amirm , many thanks, great video as always!

You referred to balanced out on a headphone amp as being only more powerful in the video. Is that really the case, or would a balanced output also be expected to change the sound characteristics as well? I recently switched to a balanced cable for one of my favorite headphones on a Topping A50s, resulting in a significant change to the sound signature of the headphones (in a much better way), in addition to the power gain. Am I totally dreaming?
Maybe not. Sometimes when there is not enough power, a headphone can sound anemic. It could also be that you are playing it louder. Both point to extra power being the factor, not something else.
 
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amirm

amirm

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Thread Starter #49
Don't do that. The two RCA connectors share a ground which means you would be shorting the negatives of the 4.4 mm balanced connector. This can damage some headphone amps.
 
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#50
Don't do that. The two RCA connectors share a ground which means you would be shorting the negatives of the 4.4 mm balanced connector. This can damage some headphone amps.
Thanks amir, you just saved me. Right now I'm using balanced cable for my headphones since my dac/amp all have 4.4mm balanced output (ifi ZEN Dac, iFi Hip DAC and Lotoo PAW S1)
 

Atanasi

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#51
4.4mm adapter can be wired compatibly with unbalanced lines, because 4.4mm has a ground wire: just taking the positive pole of each channel and the ground should work.
 

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#52
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