Balanced vs. Unbalanced Inputs

I cannot believe the arguments phrased here because of a lack of a simple circuit diagram and a bit of simple circuit knowledge.
If you wish to know the difference between a single ended circuit and a differential circuit, AND the relative grounding difference, you need a simple CIRCUIT DIAGRAM and knowledge about how circuits and especially SHIELDED circuits work. The word "ground" should be defined MUCH better for people who are "wire nuts," i.e., those who follow WORDS (OMG!) better than circuit diagrams. de KQ2E

Nice of you @nitroxpro to advance the conversation with circuit diagrams and your advanced knowledge of simple circuits.

Where is the empirical evidence of improvement using balanced connections? Any? Any at all? Oh, that's right, because there is none.  

Actually there is and its historical. So here is the history: Before balanced lines were developed, a long distance phone call was really only good to the other side of nearly any given state, and you had to be prepared to yell at the top of your voice to be heard. When balanced lines were introduced, this made transcontinental phone calls possible with greater intelligibility. The recording industry was quick to adapt the technology (in the late 1940s and this is one of the key technologies besides the invention of the tape recorder that ushered in the age of high fidelity.

The whole point of balanced cable operation is to avoid interconnect cable interaction with the sound of the system and if the tenants of the balanced system are followed, it does this very well. This means that to sound right, the cable does not have to be expensive, it simply has to be correct!

Could you clarify this, because in my mind, the point of balanced is, and has always been common mode noise rejection. Good cable construction will of course lead to consistency of noise on both cables ensuring common mode rejection.

Now w.r.t. studio balanced connections, i.e. AES compliant, that is not just about balanced, but a drive/load standard that is low enough impedance to dominate over cable parameters.

Sure. As you can see from its historic legacy, balanced lines were used to increase intelligibility. This is exactly why it made it possible to hang a pair of microphones above an orchestra, and have the tape machine 150 feet away, receiving that mic signal without degradation. Certainly noise rejection is one aspect, but so is the rejection of ground loops (that is why the balanced line system ignores ground).

No, that statement is quite true. A floating source is not the same as a differential source. It would only be truly differential if you center tapped it and connected the shield to the center tap, such that coupling to the cable shield is similar for both conductors. That is not the case for a cartridge.

This statement is a common myth, and being a myth, is false. A center tap degrades the Common Mode Rejection Ratio, on account of the simple fact that no center tap is really centered exactly. For this reason, center taps are never used. This is true of dynamic mics, cartridges, tape heads and any other inductive source including input and output line transformers. 

And than, we gonna “hear “the difference  between the 2: for me RCA is more open: good balance, beautiful placement , detailed and holographic. XLR: gives also a good balance, placement:okay, but the openness is less: “flatter” compared to RCA.  Conclusion: I only used RCA. ( my system: CEC cd-player, Auralic streamer, Metronome Technologie C6 (dac), Daniël Hertz M6L ( préamp) Wavac MD 805 m ( monoblocks) and Ilumnia Magister (speakers)

The problem here is that in order to obtain the benefit of balanced operation, your equipment must support the standard, AES48. Having introduced balanced line operation to high end audio, I can tell you that hardly any high end audio gear supports the standard and so you hear differences, and often degradation. That's a unfortunate because the technology clearly works (which is why all your recordings use it); you'd think audiophiles would be interested in something that prevents interconnect cables from interacting with their audio system. If you've ever heard differences between cables you know what I'm talking about. Imagine all the cables sounding as good as the best you've heard: that is the benefit.

I think I would be a great idea to ask the the great phono cartridge and phono amp designers to clear this up - hopefully they might all agree. Question: precisely how are cartridge and turntable wired to the phono amp to obtain fully balanced operation?

The first balanced line phono section was made by Atma-Sphere Music Systems in 1988 and offered in the first balanced line preamp in 1989. Since the cartridge is already a balanced source, its a matter of getting the signal to the preamp without involving that signal with the ground system (the tonearm tube and turntable). To this end, the plus and minus outputs of the cartridge are tied to pins 2 and 3 of the XLR connection. The tonearm ground then becomes the shield of the interconnect cable and ties to pin 1 of the XLR at the phono input. Since the phono input is balanced, it ignores ground and looks at what is different between pins 2 and 3. In other words, the signal is **received** in the differential domain. In the old days this was done with an input transformer with its primary winding simply tied to pins 2 and 3; the ground is simply the chassis of the preamp. Of course you don't need the transformer, but then you need a differential amplifier at the input of the phono circuit. This can be done with tubes or transistors. This is how our phono preamps work and the signal is kept in the differential domain throughout the preamp.


The tricky bit is that sometimes the tonearm manufacturer does not supply the arm with a removable interconnect cable. But most do, and usually if they don't (Rega comes to mind) it is possible to convert the arm anyway. Back in the old days, turntables like BSR, Dual, Garrard and so on had the tonearm wires exit the arm beneath the plinth where there was a terminal strip that had connections for the 4 cartridge wires plus the tonearm ground. That was where the interconnect cable was attached, so even for those ancient machines its fairly easy to install a balanced line simply by replacing the interconnect cable.

Thank you for all the effort in that input @atmasphere and the benefit of your wide knowledge and experience.  It throws much needed light.  I am finding this discussion very interesting as well as informative.

A.    If I understand correctly, to summarise, you say yes most cartridge arms can be wired fully balanced.  Balanced operation reduces noise, particularly in long wiring runs.


B.   "[balanced operation] prevents interconnect cables from interacting with their audio system...Imagine all the cables sounding as good as the best you've heard: that is the benefit."

Ooooh, I can see that one is going to be controversial.  You seem to be saying SQ differences between different cables arise from running single-ended, as most audiophile systems do, and not from the cables themselves.
Is it going too far to draw some further conclusions from that statement:
1.  All well-designed cables sound (much) the same in a balanced set-up.
2.  Money spent on expensive cables is (largely) wasted in a balanced set-up.  Therefore:
3.  There are SQ differences due to cables in a single-ended set-up so expenditure on cables can be justified.  But if you choose a balanced system, this will gain at least the same SQ improvements as buying expensive cables, but without the extra cost.  Pace - I accept in principle it is more costly to build balanced amplifiers than single-ended.


C.   "your equipment must support the standard, AES48; I can tell you that hardly any high end audio gear supports the standard "

Are you saying that some amplifier hardware fitted with XLRs and said by the manufacturer to be 'fully balanced', is not fully balanced and does not support AES48?  Presumably XLRs could be put on for show without the correct wiring behind?  If this is correct, someone suitably qualified should start naming names.

This statement is a common myth, and being a myth, is false. A center tap degrades the Common Mode Rejection Ratio, on account of the simple fact that no center tap is really centered exactly. For this reason, center taps are never used. This is true of dynamic mics, cartridges, tape heads and any other inductive source including input and output line transformers.

I never said that center tap would be better for noise rejection (though it absolutely could be). You appear to have have misinterpreted my use of center tap to imply a single ended ground reference, which is not the same as connecting the shield to a center tap to balance the signal w.r.t. the shield. That it is not used in audio (not needed) does not mean it does not work. It is used in other industries because it does.


https://www.pulseelectronics.com/wp-content/uploads/2016/12/G019.pdf

https://patents.google.com/patent/US20170131427A1/en

Certainly noise rejection is one aspect, but so is the rejection of ground loops (that is why the balanced line system ignores ground).

Grounds loops ARE common mode noise. Hence, the accuracy of my statement, to reduce common mode noise.

The problem here is that in order to obtain the benefit of balanced operation, your equipment must support the standard, AES48. Having introduced balanced line operation to high end audio, I can tell you that hardly any high end audio gear supports the standard and so you hear differences, and often degradation.

We are talking input to phono stages, i.e. cartridges, so not sure where you are going bringing this up. It is not applicable.


At this point we need to be pedantic since terms that are not interchangeable are being used that way, "balanced" refers specifically to the interconnect method, i.e. the signals are impedance balanced to the ground/shield, hence the noise on one is balanced and opposite to the other. That could be implemented with transformer coupling and shielded cable, or differential signalling and a shielded cable.
What is called a "balanced" input is balanced in the sense that it connects to a balanced interconnect, but electrically it is differential. The AES standard is a differential signalling standard coupled with a balanced interconnect.

Since the cartridge is already a balanced source, its a matter of getting the signal to the preamp without involving that signal with the ground system (the tonearm tube and turntable).

Which makes this statement as noted before inaccurate.  A cartridge is not a balanced source. It is a floating differential source.  If you twist the wires and maintain a consistent (w.r.t. each wire) shield to the amplifier then the interconnect would be balanced.

Because the cartridge is floating, and hence its output differential, going into single ended input, assuming you use the practices of balanced interconnection (with shielding), you can still have a low noise floor especially at low frequencies, because the common mode noise at those frequencies will be rejected. However, from a practical standpoint, this does not work well at high frequencies, due to parasitics. This is where the differential input comes in that will reject common mode not just at low frequencies but at high frequencies.

Unfortunately, too often balanced and differential are thrown around interchangeably and they are not and mean different things. This is confusing especially if you are trying for a deeper understanding.