Differential Balanced Sound Quality


I've read where running a true balanced (differential) amplifier as such sounds much better than running it single ended (I'm assuming the same amp has both balanced and single ended inputs here).

Why would that be the case? Is it merely the improved SN ratio, etc. from being balanced, or is it something circuit related with running each channel's plus and minus through separate amplification stages?
greg7
The bit that a lot of people are unaware of is that balanced inputs are actually noisier than single ended (RCAs etc.) in that they utilise relatively high value resistors that introduce their own (johnson) noise into the signal.
This statement is problematic. There’s no reason why any such ’high value resistors’ be used in a balanced circuit that aren’t also in a single-ended circuit.
Because it is so obviously the wrong way to go. The number one factor in quality sound is quality parts. Going balanced requires twice as many parts. A whole duplicate circuit.
@millercarbon This statement is false and is a common myth: it ignores the bit about ’differential’. If the circuit employs differential amplifiers, then the parts count is about 50% higher rather than double. There is a distinct advantage to differential amplifiers (which are often used in amps with single-ended inputs, as they are often used as phase splitters); they have much more power supply noise rejection and if the circuit is fully differential, then even ordered harmonic distortion is cancelled at each stage throughout the circuit, rather than compounded (which can increase higher and odd-ordered content).


There is an advantage to this- when the circuit is fully differential, the primary distortion harmonic is the 3rd, which is treated by the ear the same as the 2nd in that it contributes to ’bloom’ and ’warmth’. But in such a circuit, the 3rd will often be at a 10th of the value that is seen in a circuit that has a 2nd harmonic as the primary distortion component. In mathematical terms, the former has a cubic non-linearity whereas the latter has a quadratic non-linearity. When there is a cubic non-linearity, succeeding harmonics drop off at a much higher rate than they do if the non-linearity is quadratic. In a nutshell, fully differential circuits are much lower distortion and so sound more neutral. This is not subtle either- its easy to hear. So there is a distinct advantage to all those extra parts if the designer took advantage of all the aspects of differential operation!
Balanced is totally designed for professional use. Runs of hundreds of meters. Not tens of feet.
This statement is also false. The benefits of balanced line connections are there even if the connection is only 6 inches. I can go into it further if you like; FWIW this idea of ’only for long distances’ is also a common myth. Think about this- you don’t have to know the technical side; the simple fact that you can run such long distances without coloration is a tip off that those colorations won’t be in a 6 foot run either! If you’ve heard differences between single-ended cables, then you know what I’m talking about when I use the word ’colorations’.
I’m not a fan of preamp to amp balanced connections. I’ve always preferred single ended overall. YMMV
@geof3 The reason balanced operation might not seem to bring home the bacon in high end audio is that there is a standard for balanced line operation, which most high end audio manufacturers do not support (and don’t seem to realize how this degrades the sound). When the standard isn’t supported, the cable construction becomes audible like it does when running single-ended. Balanced operation isn’t two single-ended signals running together in a cable! Its a single signal traveling in a twisted pair with both sides ignoring ground. Please Note that I am not arguing with you here- I’m sure that what you’ve experienced is very real. But what you experienced was not how balanced operation is supposed to work. BTW, the balanced line standard is known as AES48. You can always ask the manufacturer if their equipment supports AES48; if they don’t know or don’t know what it is, then its a very safe bet their gear doesn’t support the standard and so will not demonstrate all the advantages of balanced operation.


Those advantages are:
1) lower noise (blacker backgrounds)
2) neutral, transparent interconnect operation regardless of length (more detailed, less colorations resulting in no need for expensive interconnections)
3) no ground loop noise or intermodulations (not as harsh)

But if the standard isn’t supported these things go away and as you’ve heard, might even be worse.


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@atmasphere Ralph, apparently we posted at the exact same time.  Any facts of operation I got wrong in mine?  As always, thanks for your contributions...
@atmasphere - Ralph - another excellent explanation. Thanks. 

I've been a big fan of balanced circuitry and cables since I discovered what a difference they could make in my system in the late 80s. Never looked back.
Also, I took the opportunity to read the article I linked. It has lots of good information about the 2nd harmonic, but none about the 3rd. Here’s some more Pass writing that discusses both:

https://www.passdiy.com/project/articles/audio-distortion-and-feedback

And here in the introduction (on p3): https://www.firstwatt.com/pdf/art_ba_3.pdf