Understanding Balanced Audio (video)

[DonH56]

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]

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

 

[semektet]

@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]

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]

... 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.

 

[goldenpiggy]

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.

 

[amirm]

@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.

 

[sulfuriq]

Is there any benefits if using 4.4mm output to dual RCA for an active speaker that doesn't have XLR input?

 

[amirm]

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.

 

[sulfuriq]

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]

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.

 

[Nango]

Thanks amir, I was one of the posters that was confused about the balanced and differential terminology used. For a more technical understanding, is there a circuit/signals book that can be pointed to (I'm comfortable with mathematics)?

https://robrobinette.com/Push-Pull_Vs_Single-Ended_and_Balanced_Vs_Unbalanced.htm

https://robrobinette.com/BalancedCable.htm

 

[AnalogSteph]

Rod Elliott has three articles on things balanced online, notably part 2:
https://sound-au.com/articles/balanced-2.htm
and part 3:
https://sound-au.com/articles/balanced-io.htm

 

[luft262]

Thank you for this educational video Amir! Would it be possible, from your chart of headphone sensitivity/efficiency, to tell at what point when going up the graph in inefficiency the headphones will start needing one, then two, the three etc. volts or watts of current to run those headphones at a loud, but listenable level? Thanks again!

 

[Yorkshire Mouth]

Q1 - If Ihave a pair of easy-to-drives headphones like AKG K371s, and I’m not experiencing ground loops, is there any advantage in upgrading to ‘balanced’ for any reason other than future-proofing?

Q2 - I’ve I have a PC, a DAC, a headphone amp, and a pair of phones, and I’m not getting any audible ground loops, might j get them if I change any one piece of kit, or would I already be able to hear it?

Many thanks.

 

[Curupira]

Hey @amirm , I saw the video and in one moment you mentioned that the XLR balanced input has nothing to do with the balanced output of the amp, and therefore you could have RCA inputs while outputting balanced XLR. I get that from the point of an electrical signal coming through and being distributed to the outputs. My question then is, doesn't that make any difference in regards to power and voltage? I mean, could I reap the benefits of greater power of the balanced outputs while still inputting 2V with RCAs? Or is that strictly dependent upon the amplifiers internal design? And thank you for the vid!

Also a question about cables: I'm studying modding my DT 880@600 to make it balanced capable down the road, and for that I'm using a socket for each side with a ground and a positive/negative connected to each driver, like this:

Spoiler

I'll only use two pins (big ground and one of each of the little ones) per side. My question therefore is whether I could use a normal unbalanced cable with this as well. My understanding of it is that when connected by an unbalanced cable the individual grounds on each side will just short out in the end and there will be no problem (like with an unbalanced HD 6x0), and when using a balanced cable they won't be shorted or shared, and will go like that until the connector. Am I right about this?

 

[DonH56]

Why not use an XLR, a standard connector?

The convention for interfacing balanced to unbalanced is to leave the (-) balanced output floating and just route shield and (+) output to the RCA ground and (+) input respectively. That obviates shorting one side of the balanced output. Opinions vary a bit on how to connect a single-ended output to a balanced input and it somewhat depends upon the circuit configuration of the balanced input. You connect RCA (+) to balanced input (+), then decide whether to connect RCA (-, ground) to the balanced (-) input, shield, or both.

The XLR connector has shield (earth) and chassis ground connections, which is more complex and also more flexible if you want to prevent a ground loop and keep noise rejection as high as possible. There are several manufacturer's app nots on this from companies like Rane, Crown, etc. This article is pretty comprehensive and is oft-cited: https://www.ranecommercial.com/kb_article.php?article=2107 Reading through it a few times may be very worthwhile.

HTH - Don

 

[Curupira]

Why not use an XLR, a standard connector?

The convention for interfacing balanced to unbalanced is to leave the (-) balanced output floating and just route shield and (+) output to the RCA ground and (+) input respectively. That obviates shorting one side of the balanced output. Opinions vary a bit on how to connect a single-ended output to a balanced input and it somewhat depends upon the circuit configuration of the balanced input. You connect RCA (+) to balanced input (+), then decide whether to connect RCA (-, ground) to the balanced (-) input, shield, or both.

The XLR connector has shield (earth) and chassis ground connections, which is more complex and also more flexible if you want to prevent a ground loop and keep noise rejection as high as possible. There are several manufacturer's app nots on this from companies like Rane, Crown, etc. This article is pretty comprehensive and is oft-cited: https://www.ranecommercial.com/kb_article.php?article=2107 Reading through it a few times may be very worthwhile.

HTH - Don

Thank you for responding Don! I hadn't thought on using an adapter, my first questions background is that I own a RCA out only DAC (Loxjie D30), and so it only outputs 2V. So I wonder if I could get a balanced capable amplifier like the A90 and still get the full power rating through the balanced headphone out, because I always got the impression that in my scenario I would cap the balanced out potential just by feeding it 2V

 

[DonH56]

Thank you for responding Don! I hadn't thought on using an adapter, my first questions background is that I own a RCA out only DAC (Loxjie D30), and so it only outputs 2V. So I wonder if I could get a balanced capable amplifier like the A90 and still get the full power rating through the balanced headphone out, because I always got the impression that in my scenario I would cap the balanced out potential just by feeding it 2V

Depends upon the DAC's max output and amp's gain, natch. And just how much signal you need to make your ears bleed.

 

[Curupira]

Depends upon the DAC's max output and amp's gain, natch. And just how much signal you need to make your ears bleed.

It is 2.3v by ASRs measured unit and I have +9db gain over the amp. That is practical but I guess you already answered my question hahaha. So the DACs max output determines the rest of the chain. Only thing left unanswered then is whether there would be a difference in output voltage in the amp while using the RCA in by that 2V margin, or, in other words, if SE perfomance will be the same as bal out while using RCAs.

Spoiler

And about my deafness. Fear not, it is just that the 600ohm beyer can seem quiet on vinyl or with EQ on digital. I'm now adding gain on the phono stage, but still wonder if I'd profit from getting a balanced amp (prolly not because that would mean also changing the phono for balanced...)