Balanced vs RCA between amp/preamp

https://benchmarkmedia.com/blogs/application_notes/balanced-vs-unbalanced-analog-interfaces?_pos=1&_sid=87340c17d&_ss=r

A lot of informative info before this summary in the link above.

SUMMARY

Professional-grade balanced analog audio interfaces can provide a 12 to 16 dB SNR advantage over unbalanced interfaces due to the high +24 dBu signal levels used on balanced interfaces. Consumer-grade balanced interfaces can only provide 3 to 6 dB SNR advantage due to the relatively low +14 dBu (4 Vrms) signal levels.

In addition, the differential amplifier or transformer in a balanced input can provide an incredible 50 to 100 dB rejection of ground-loop interference. This is usually sufficient to reduce ground-loop interference to completely inaudible levels.

In an unbalanced interface, the shared use of the shield places ground-loop currents in the audio path. Unbalanced interfaces are very sensitive to ground currents flowing between audio components. This is not a problem with balanced interfaces due to the use of dedicated audio conductors.

Copper braid and foil layers provide shielding against RF interference. In a balanced cable, the shield does not carry the audio signal. The audio conductors are fully surrounded by the shield but are electrically isolated from the shield. In an unbalanced system, the RF shield also serves as the audio ground. This dual use of the RF shield, in an unbalanced system, causes a slight increase in susceptibility to RF interference.

Copper braid and foil shields do not provide any protection against magnetic interference. Magnetic fields easily pass through copper and foil. If star-quad cables are used in a balanced system, magnetic interference can be rejected by the CMRR of the balanced input receiver. In a balanced system, 4-conductor star-quad cables can reduce magnetic interference by 20 to 50 dB when compared to standard two-conductor balanced cables.

These numbers should be hard to ignore, but the hi-fi industry has been slow to change. Many high-end audio products still are not equipped with balanced interfaces. Others have consumer-grade 4 Vrms balanced interfaces. These are a partial step in the right direction.

The facts show that it is virtually impossible to achieve state-of-the-art audio performance using unbalanced interfaces. We see this in the lab when we measure balanced and unbalanced interfaces under ideal well-controlled conditions. Outside, in the real world, the advantages of balanced interfaces are larger than a set of balanced vs. unbalanced specifications would indicate on a product data sheet. The differences can be extremely large when ground loops, RF interference, and magnetic interference are encountered in a typical audio system.

Our recommendation? Avoid unbalanced (RCA) analog interfaces whenever possible! Look for professional-grade balanced interfaces when buying audio products. Look for CMRR specifications on balanced inputs. Consider replacing audio devices that do not support balanced interconnects. These unbalanced-only devices are probably a weak link in your audio chain.

that being said your Amplifier and preamp need to have transformers for the input,outputs to be what is considered a True balanced .

This statement is false. You don’t need transformers, but without them supporting the balanced standard gets a lot trickier. We developed a means that is direct-coupled and yet floats the same way that a transformer winding does.

Many owners of Atmasphere gear (amps to preamps....all balanced) have reported the same cable differences that others have reported on other balanced gear.

Oddly, they’ve not been reporting them to me.

A balanced signal is simply two unbalanced signals, one 180 degrees out of phase (mirror image).

This statement is incorrect. With a proper balanced signal, the non-inverted phase is created with respect to the inverted phase, **not ground** (which is for shielding only). So its not two unbalanced signals- its only one, which floats with respect to ground (IOW, if you wanted, you could run a balanced signal with only two wires by simply omitting the shield)! This fact is poorly understood, but think of a line transformer- it does not use a center tap- one side of the output winding is tied to pin 2 of the XLR, the other side to pin 3. No ground connection at all. **Balanced lines if properly executed ignore ground**.


So it isn’t two single-ended signals- although a lot of manufacturers think it is, and in so doing degrade the performance of the balanced connection (and allow for interconnect cable artifacts and ground loops to creep into the system sound equation). When we built the world’s first balanced line preamps back in 1989, it didn’t occur to us that we could do that without supporting the standard. I was a bit shocked when I started to see other balanced gear that in no way supported the standard, and then exotic interconnects appeared because they were needed to work with such substandard equipment. You’d think that audiophiles would jump at the chance to no longer have to spend big $$$$ on cables and yet still get the best results...


In a nutshell, here is the standard:
1) pin 1 ground, pins 2 and 3 are signal. Pin 2 in the US is non-inverted side of the signal
2) ground is ignored, the signal floats; the pin2 signal is created with respect to pin 3 and vice versa
3) the system is low impedance- if there is an output XLR, its able to drive 1000 to 2000 ohms with ease (the old standard was 600 ohms and our preamps support that)
4) the signal travels in an interconnect consisting of a twisted pair with an independent shield.

I clearly said that the pin lengths on the male connectors of my XLR cables appear to be the same for all of the pins. It is the female connector for which I described a difference, which when mated with a male connector having equal length pins would result in the ground connection being made first, upon insertion, and removed last, upon removal.

Al, for all these decades of doing balanced connections, I’d never noticed that. You have to look quite closely at the female connector!! @millercarbon, my apologies on this point.

the sound of the interconnect won't be a thing

Malarkey!

Assuming balanced circuitry and connections are properly implemented, which far too often they are not, they can reduce common mode noise. FULL STOP.

For balanced interconnects to be immune to cable, they would have to be immune to the laws of physics. Balanced lines [and connectors] have impedance and impedance controls frequency response.

differential amps tend to be lower noise we don't need as much gain stages to get the job done

If number of stages is a criteria, use a transformer. Differential amps per se are all over the map in terms of gain vs noise. The devil is in the details.

the other reason for balanced lines is elimination of ground loop noise

I'll wager that 6 9's of 'balanced' home audiophile systems do not lift the shield at the destination. Depending on amplifier design, there may be ZERO ground loop improvement over an unbalanced system.

The balanced line system was created to get rid of interconnect cable colorations

The balanced line system was invented by the telephone company to increase noise immunity and power transfer over long distances. Nominally 600Ω, but at 1 frequency ONLY! Low frequency performance is abysmal.The 'telephone sound' is a direct result of balanced cables.

The single biggest improvement I ever made to my system was when I switched from RCA cables to XLR balanced but I am not using Marantz gear I am using Atma-Sphere so YMMV.

A note about balanced pro audio...In my long career as a concert soundman, I can attest to the fact that NOBODY unplugs a balanced anything while the system is powered up, and if somebody does I will possibly throw them out of the building. The balanced connections DO NOT stop noise when unplugging live connections.