Balanced vs Unbalanced?

How does balanced work in an amplifier? IE - compared to amplifiers that have XLR in but don't employ true balanced?

A fully balanced amplifier maintains separate signal paths for each of the two input signal polarities, all the way to its output terminals. So the negative or black speaker terminal is not connected to ground as it would be in an unbalanced amplifier, and is actively driven with a signal. The signal is similar to the one on the red speaker terminal, except that it is inverted.

An amplifier that is unbalanced/single-ended internally but has a balanced (xlr) input feeds that input into a differential receiver stage that has a single-ended output. That single-ended signal is fed into the rest of the amplifier circuitry, which is unbalanced.

Re the original question, several advantages (or at least theoretical advantages) of fully balanced design have not yet been mentioned. These include cancellation of some forms of distortion that may otherwise be generated internally; and, particularly in the case of a power amplifier, lower levels of power supply-related noise. There are some others as well. See this Atmasphere white paper.

My feeling is that both single-ended internal design and single-ended interfaces are inherently compromises, assuming equal quality, starting with the fact that in nearly all modern designs that have single-ended interfaces signal returns, circuit ground, chassis ground, and ac safety ground are all common. However, there seems to be ample anecdotal evidence that in most systems and for most people the degree of that compromise is either insignificant or is overshadowed by many other variables, one of which is price.

Regards,
-- Al

Audiogalore, I've never heard there was less chance of phase shift in a balanced circuit, Could you please explain?

Very well put Al....PRICE!!! and no interferes from shared chassis ground and other component signal returns.

Alright, there is a fair amount of misinformation in this thread, and I thought since we essentially introduced balanced line operation to high end audio, I thought I should correct the misinformation herein and explain some of the whys.

Balanced operation exists for the sole reason of reducing/eliminating artifact in the interconnect cable. It will do so regardless of how long or short(!) the cable is. If it is set up right, it will always outperform single ended cables.

Balanced operation does not require twice as many components!! That is a very common myth. This is true even if the the preamp or amp is fully balanced. Now some balanced cirsuits will require twice as many components, and you will find that they also do not perform as well. The best balanced circuitry will also be differential. Differential circuits do not double components.

You can also run balanced operation without balanced components and realize all the benefits of the cables. This done via the use of transformers, as any transformer can convert from balanced to single-ended or vice versa, simply due to how its hooked up. I don't like transformers myself, but in cases where its either long interconnects or long speaker cables, the transformers and long interconnects will win out easily.

When I said that balanced operation is devised to eliminate cable artifact, I meant it- the cost of the cable becomes unimportant. However, to accomplish this, the balanced system has to be **low Impedance** (600 ohms is the standard, IOW what is driving the cable should be able to drive 600 ohms without distortion or loss of low frequencies). It is this last bit that has 90% of high end audio products falling flat on their collective faces, and is the reason why there is controversy about balanced at all. IOW if you don't embrace the standard, your balanced setup will be no better than single-ended and possibly worse.

Now if the components involved are internally balanced, you will realize two benefits: lower noise per stage of gain, and distortion cancellation with each stage of gain. So balanced preamps and amps can take advantage of that by using less gain stages as a result. This means that they will be more transparent, as reducing distortion reveals detail. I can expound more on that if you like.

Phono cartridges are balanced sources so LP can be run from needle to speaker fully balanced. The same is true of microphones and tape heads. CDs may or may not be balanced, but there is still advantage to using balanced operation with them due to the advantages of the interconnect itself. This is **not** to say that if your CDP is single ended that you can just stick a balanced cable on it and it will get better, it means that if you use it with a balanced preamp, the preamp will handle the signal fine and it will be delivered in better condition to the power amp.

I am certain I have forgotten a number of points but I expect they will come out in the responses to this post. The bottom line though is that balanced operation is a pathway to greater resolution and lower noise than is possible with single ended, but only if the standard is embraced.

I did forget something- a request. There are those of you here that disagree with my prior post and will have talking points. Please keep them if you can to one talking point at a time, so that we can be clear that they get responded to in a coherent fashion. Thanks!