Simple Graphical Guide on Single-Ended vs. Balanced Audio with Headphones
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ClieOS

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Wrote this for some place else but I guess it is just as relevant here. Probably be better to post it in the Wiki section, but it doesn't seem to be working right after the forum update. So here it is.



A ‘single-ended’ source is the kind of normal audio source with a 3.5mm or 6.35mm stereo socket. It has a left and right channel going to the headphone’s drivers and a ground channel going back to source to complete the circuit. In a single-ended circuit, only left and right channel carry active signal while the ground channel doesn’t (passive / zero volt). FIG 1 is a simple representation of how most single-ended setup looks like



The origin of balanced audio is really from pro-audio’s stage usage. In a pro-audio environment that usually involves a lot of different very powerful electronic equipment running on the same time, RF interference can easy cause a lot of noise to a single-ended circuit, especially when long transmitting cable is used (which acts more or less like an antenna). The idea of balanced audio is to generate an inverted signal from the left and right channel, thus resulting in Left+ (original left signal), Right+ (original right signal), Left- (inverted left signal) and Right-(inverted right single). When the two pair of signal are sent over distance, any extra signal that can’t be cancelled out by the opposite pair can be identified as noise caused by the RF interference and subsequently being eliminated to reproduce the clean left and right signals. However, the inherent benefit of driving headphone with balanced signal is not because of noise, as headphone generally doesn’t have nearly as long a cable as pro-audio usage and thus doesn’t pick up much interference, but because balanced audio has: (1) Double the slew rate when compared to single-ended circuit as the opposite (inverted) signals having a ‘push-pull’ like relationship when compared to single-ended circuit where left / right signals are sinking into the same zero volt ground channel. This results in better transient for balanced audio. (2) Better channel separation since balanced audio does not share a common ground channel (which in fact is not requited in balanced headphone setup). Some might think balanced output on the same source will always give double the driving power than single-ended output – this is however not always true, depends on how the source is designed. With the right design, it is possible that the single-ended output performs just as good as the balanced output. FIG 2 is a simple representation of how most balanced setup looks like.



FIG 3 shows how the Pentaconn 4.4mm connection can also be used to power a single-ended headphone even though the source has a balanced output. This will required both the source and headphone to be designed and wired correctly. Not all Pentaconn 4.4mm enquired balanced source can be utilized in such way and you should consult with the source’s manufacturer first.



FIG 4 shows how you can convert a balanced headphone with the right adapter to be used on a single-ended source. Basically the adapter will short the headphone’s Left- and Right- wires together to be used as ground channel and effective turns it into the same configuration as a single-ended headphone.



FIG 5 shows you instead an incorrect utilization of adapter to connect a single-ended headphone to a balanced source. While you can convert balanced headphone to single-ended configuration by adapter, you cannot convert single-ended headphone to balanced configuration by a simple adapter. You will need to rewire a single-ended headphone’s cable in order to create a separated path for the individual Left+, Right+, Left-, and Right- signal – and an adapter will not do that. What this kind of adapter does is to simply short circuit the Left- and Right- channel together. Unlike ground channel, which has zero volt, Left- and Right- are active channel and they will not cancel each other out. In the best case scenario where the source has built-in protection circuit, using this kind of incorrect adapter will only decrease the sound quality and performance of the whole setup, besides messing up the stereo image of the music. In the worst case scenario where the source does not have any built-in protection circuit, it is possible to permanently damage the source’s circuit. In other words, never try to connect a single-ended headphone to a balanced source (with the only exception of what shown in FIG 3). Sometime you will find people selling this kind of adapter on ebay, Taobao or Aliexpress – do not get fooled!
 
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ClieOS

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Reserved.
 
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Pardon me, but I am a little confused per quote:

Some might think balanced output on the same source will always give double the driving power than single-ended output – this is however not always true, depends on how the source is designed. With the right design, it is possible that the single-ended output performs just as good as the balanced output

End quote
Yes, technically, balanced is more powerful....but then...I question

So, with the right design, SE can sound just as good as balanced ? Then the double slew rate and better separation due to not using the same common ground won’t be the real advantages ?
 
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ClieOS

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Pardon me, but I am a little confused per quote:

Some might think balanced output on the same source will always give double the driving power than single-ended output – this is however not always true, depends on how the source is designed. With the right design, it is possible that the single-ended output performs just as good as the balanced output

End quote
Yes, technically, balanced is more powerful....but then...I question

So, with the right design, SE can sound just as good as balanced ? Then the double slew rate and better separation due to not using the same common ground won’t be the real advantages ?
Good question.

Let simplify it and assume the SE circuit in question is made out of just one opamp ("X"), then a balanced circuit based on the same design will requite 2 opamp X per channel;(one for original signal and one for inverted signal). Opamp X has a slew rate of Y (and thus SE circuit has a slew rate of Y) - since balanced circuit has a push-pull like effect, 2 opamp X will give you slew rate of 2Y (one pushing and one pulling) - but that is only limited to the condition that the balanced circuit is double of the same SE circuit, which might not be always the case.

Say you build the balanced circuit with 2 opamp X that give you slew rate of 2Y, but you build the SE circuit with another, faster opamp ("Z") that already has a 2Y slew rate - then obviously the slew rate of both your balanced (2 opamp X) and SE circuit (1 opamp Z) will be the same - this is what I mean by 'the right design' - There is no rule that mandate anyone to build their SE circuit as half of the balanced circuit (or balanced circuit as double the SE circuit) inside the same source. By creating two different circuits with different parts, it is possible to get very similar performance.

This is also the same reason why some balanced output do not have double the output power as the SE output on the same source - because they can be different circuit in parts or design.

SE separation on the other hand is harder to get as good as balanced simply because of the share ground channel - but it can be designed to be good enough to compete with balanced circuit.
 
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Nicely explained. Agree on all.
May I add to this.
small portable DAC/amps such as Fiio or ES100, max. power output is limited by their battery's voltage, this is usually low.
there are ways to boost this, one is a DC to DC conversion to boost the voltage, but not very practical, as it produces a lot of noise, costs too much.
Another way is to use two amps, or even two DAC-Amps.
There are a number of off-the-shelf chips available from the likes of SABRE, that are a DAC chip with an amp onboard!
They are cheap enough, so two are used per channel (or a stereo chip). the signal being fed to one DAC is digitally inverted to produce a left-inverted and right-inverted, as well as standard right and left.
using the output from these stereo chips, a balanced output can be obtained, that has twice the slew rate, twice the voltage swing (4 times the power) and some unwanted common artefacts can be rejected by the nature of the "push-pull" analogy already mentioned.
This explains why such devices, produce more power in balanced mode, use more battery juice, and possibly sound better. By completely separating the right and left channel DAC-Amps, stereo separation can improve too.
I offered a simple explanation of this phenomena here:
https://www.head-fi.org/showcase/fiio-btr5.24178/reviews
 
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