This article is meant to clear up some misconceptions about balanced operation. There are a lot of myths about how balanced lines and balanced equipment is supposed to work; I've written extensively about that on the web in various forums so it seems that if I put everything in one place at the same time it will be less work!
The balanced line system was first created for telephone land lines. It made transcontinental and intercontinental phone calls possible. It was adopted by the recording industry in short order and all high fidelity recordings spanning over half a century since use this system. If you've ever wondered how any record label could make a high fidelity recording, when the microphone signal had to travel over 150 feet to get to the microphone preamps, yet without the benefit of modern exotic interconnect cables, the balanced line system is how.
We were the first High End Audio company to produce a product for home use that supports the Balanced Line Standard, also known as 'AES48'; Audio Engineering Society File 48.
In high fidelity the advantage of balanced lines is :
- Lower noise from sources external to the cable (or the signal), such as power transformers
- Far less sonic fingerprint from any given balanced cable
- Longer lengths are possible, but the benefits are realized even if the cable is only six inches long
- Ground loop noise is vastly reduced or eliminated.
Audible Cable Differences?
If you have ever had to audition a cable, if you have ever heard differences between two cables, then you already know the answer to this question. If executed correctly, balanced lines eliminate the cable artifacts that cause audiophiles to audition cables. Audio engineers work in environments where balanced lines are in common use, and so they are used to this fact. Audiophiles often don't work in such environments and so are very used to having to audition all their cables. Imagine a system in which inexpensive cables can sound as good as the very best or most expensive cables; that is the balanced line system.
The trick here is that balanced lines are driven in a completely different manner as opposed to single-ended operation. In a single-ended system, the cable has a signal connection and a shield. The shield is the 'return path' for the signal- it must make a connection in order to complete the circuit. Otherwise the result may well be a loud hum. In a balanced system the drive is quite different- the ground (which is pin 1 of the XLR balanced connector) is not used for the signal at all. Instead, the signal floats and so has two aspects, inverted and non-inverted. Thus the signal travels in a balanced cable via a twisted pair of wires within a shield. The inverted aspect (pin 3 of the XLR connection) is referenced with respect to the non-inverted aspect of the signal (pin 2 of the XLR connection).
In the old days of the 1950s and 1960s when the vacuum tube was king, this was done by using a transformer to convert from the audio circuit to the balanced connection. In this regard, the output of the transformer was a simple secondary winding of the transformer. One end of the winding was tied to pin 2 of the XLR connection; the other side to pin 3. Note that there is absolutely no connection between the transformer and ground, other than it was likely mounted to the chassis of the equipment in which it resided.
In more modern times (1970s until now) solid state equipment began to appear for studio use that also had balanced outputs. With pro gear, this still meant that an output line transformer was used. But with so- called 'semi-pro' gear, like early Tascam mixers that became available inexpensively, balanced outputs were often executed using opamps. Now it is possible to use opamps quite successfully with a floating balanced output, but Tascam chose to drive their balanced outputs with respect to ground rather than with respect to its opposite. This put signal return currents in the cable, which degrades the cable performance, but because the gear was used in the home or in smaller studio situations, this wasn't important and so a trend was introduced- balanced line equipment that didn't support the balanced standard.
The Balanced Standard
At this point it is good to review what the balanced standard actually is; here it is in a nutshell:
- The balanced connector is usually the XLR, which has 3 pins: pin 1 is ground, pin 2 is non-inverting and pin 3 is inverting
- Ground is ignored; used for shielding only
- The output impedance of whatever is driving the connection is low so it can drive a load of 2000 ohms or lower.
- The signal travels on a twisted pair within a shield.
- Both sides of the signal connection have an equal impedance to ground and may be floating
- No center taps are employed for transformer connections.
Balanced Line Myths
Here are some common myths about balanced lines:
- It is only useful for longer connections not seen in the home.
- Single-ended sounds better
- A center tap is required for a cartridge or tape head to operate balanced
- A tone arm has to be modified to run balanced
- Balanced equipment has twice as many parts
The Truth of the Matter
Balanced lines offer advantages even if the connection is only 6" long, although it is also helpful for longer distances. For example if you have monoblock amplifiers, they can be placed very close to the loudspeaker, allowing for a short speaker cable. This allows for increased resolution and likely more bass impact. In the case of a phono cartridge or tape head, the connection might be a meter, but as any audiophile knows, the input cable from such sources is often the most important to get right in the entire system. A cable that has no sound of its own is obviously helpful in such situations! With balanced line it also does not have to be expensive.
The reason balanced line sounds better is because the cables have less impact on the overall sound (in other words they are more neutral). This is because ground currents of the signal are not present in the shield and because the system is relatively low impedance, which swamps capacitive and inductive aspects of the cable. Single-ended does not have this advantage!
Phono cartridges and tape heads are essentially a coil floating in space. This is the ideal balanced source, since each side of the coil has an equal impedance to ground. The reason a center tap isn't used in such sources (and also balanced line transformers) is that the center tap can't be placed perfectly at the center of the coil. If the center tap is off just a tiny bit, the Common Mode Rejection Ratio (CMRR, a measure of the system's ability to reject signals that are common to both sides of the balanced line) will be degraded significantly. So no center tap is used. Instead, each side of the signal is referenced with respect to its opposite. In a cartridge, this means that the plus output is referenced with respect to the minus output and neither side is ground. Again, ground is only used for shielding. In a cartridge, this means the tone arm as well as the cable shield.
Benefits of equipment that is internally balanced
Balanced line equipment is often also fully differential, like our amps and preamps. A differential amplifier has two inputs, and in theory only amplifies what is different between those two inputs; any signal that is common to both inputs is rejected. This ability to reject common signals is called Common Mode Rejection Ratio (CMRR), and is measured in decibels (our differential circuits tend to have CMRR decibel values in the high 90s to low 100s). Such an aspect does not exist in single-ended circuits; noise that gets into the signal simply gets amplified.
A differential circuit isn't double the number of parts of a single-ended circuit, although it does have more parts. Quite often its about 50% more parts, but the signal path may well involve less stages of gain. Differential circuits can have up to 6db less noise of their single-ended counterparts, and that advantage adds up over succeeding stages of gain. For example, our preamps have only 3 stages of gain between the low output moving coil (LOMC) input and the main output of the preamp. That's less than any single ended preamp. When you have less noise, you don't need as much gain; with less gain stages there is less distortion and a chance for wider bandwidth.
The power supplies in balanced audio equipment see a more constant load with less noise. In turn, each gain stage is also less sensitive to noise in the power supplies. The more differential each gain stage is, the better it rejects power supply noise and the lower the noise the power supply will see in turn.
Equipment that is internally balanced and differential has a distortion signature based on the 3rd harmonic rather than the second. The ear treats these harmonics in a very similar fashion, but a circuit that has a 3rd harmonic as a fundamental distortion product is also a circuit that overall has lower distortion regardless of the harmonics. Less distortion translates to smoother and more detailed, the latter due to the ear's masking principle, which means that distortion can mask low level information. Since the ear converts all distortion into some form of tonality, having lower levels of higher ordered harmonics means there will be less perceived harshness and brightness. So going this path allows for more detail while at the same time being smoother and more relaxed; more like real music.