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balanced is inherently flawed

A recent post asking for opinions on balanced vs. single ended got me thinking once again about the inherent flaws in a balanced scheme.

A balanced signal has 2 parts called plus (+) and minus (-) that are equal in voltage but opposite in polarity. Therefore a balanced amp is really 2 single ended amps in one package, one for the + singal and the other for the - signal. So a balanced amp using the same quality parts as a single ended amp will be twice as expensive. Strike one.

That brings us to the "equal but opposite" notion. In order for this to work as planned, all of the + stages and cables connecting them must be exactly equal to all of the - stages all the way through the source, preamp, and power amp. Any deviation from the + stage being the exact mirror image of the - stage will result in an imbalance. Since perfect symmetry cannot be achieved, especially with tubes, distortions are introduced. Strike two.

Some think that balanced has to be better for various reasons that include:

1. If they hook up a balanced device using single ended cables they loose some gain.
2. They think a balanced system can achieve a lower noise floor.
3. They have balanced equipment and it sounds better when they hook it up with balanced cables vs. single ended cables.
4. It's used in recording studios by the pros so it must be better.

These arguments are flawed for the following reasons:

1. More gain does not equal better sound. Of course you need enough gain to drive your speakers to satisfactory levels, but the fact that one connection has higher gain than another has really nothing to do with sound quality.

2. This is the most misunderstood of all. A balanced amp CAN reject noise that is coming in through the interconnects. However, it can do nothing to reject or cancel the random electrical noise that comes from within the devices inside the amp. A balanced amp has no advantage over a single ended one when it comes to the major contributor of noise in the system, that which is generated inside the amp. The rejection of noise from cables relies on the fact that it is generally equal to both the + and - inputs and is therefore cancelled, but since the noise voltages generated by the devices inside the + and - stages in the amp are random and unrelated, they do not cancel and are passed on to the next stage.

Furthermore, since well designed, shielded interconnects of any type are very good at rejecting electrical noise from the outside, balanced has no advantage except in very noisy enviroments or when using very long runs, both of which apply to recording studios, not to typical home systems.

3. Since a truly balanced amp was built from the ground up to operate in a balanced mode, it makes sense that it will sound worse when fed a single ended signal. That doesn't mean that balanced is better, just that that particular amp sounds better when fed a balanced signal.

If you subscribe to the theory that more money can get you better performance, and since a single ended amp has 1/2 as many components as an equivalent balanced amp, it stands to reason that if the designer put as much money and effort into designing a single ended amp, it would sound better.

4. See 2 above.

And this brings us to our last point. ALL sound sources are single ended. Whether from a plucked string, blowing air through a horn, the human voice, or anything else; the resulting increses and decreases in air pressure that we perceive as sound are single ended. There is no "equal but opposite" waves of pressure. This is also true when the signal finally gets to a loudspeaker. There are no "equal but opposite" pressure waves coming from the speaker. It is a single ended device.

In a balanced system these pressure variations are picked up by a microphone and then some where along the line converted to balanced. A phonograph record is encoded single ended as is a digital disc. Your CD player may have a balanced output but the data that is read from the disc is single ended and then converted. In order not to introduce ditortions, this conversion from single ended to balanced has to be done perfectly. And since it can't be, strike three.
herman
jmcgrogan2's avatar
jmcgrogan2
6,346 posts
 
Well, you sold me. I guess I'll be taking out ads to sell all of my gear. Good job, I hope you're happy.
eldartford
4,262 posts
 
Although I think that balanced lines are unnecessary in the home audio situation, it is wrong to say that they are "inherently flawed". Balanced lines will do no harm, except to your pocketbook. My main complaint is that home audio manufacturers charge exorbitant prices for the little bit of extra circuitry involved, and make exaggerated performance claims to justify the price. Pro sound manufacturers routinely provide balanced interfaces at no great cost.
sean
6,231 posts
 
Herman: All i can say is "great minds think alike" : )

I just posted or emailed someone stating much the same thing. Sometimes i do so much typing that i get confused whether what i sent was public or private.

The part that stuck out in my mind about balanced operation was primarily the fact that you have four amps ( or four circuits ) doing the work of two ( for stereo ). Most manufacturers have a hard enough time building two channels that match, let alone four that perfectly match. Not only does this increase the potential for a channel to channel ( left to right ) imbalance, but also that of inter-channel imbalance ( positive to neutral vs negative to neutral ). It is hard to achieve cancellation of spurious external noises when the amplifier circuit itself may not be properly "nulling" the offsets. Then again, some of these problems would show up in S/N ratio measurements if they were severe.

If the amplifier were not properly nulling the differenctial signal, the distortions produced from such a mismatch could be corrected relatively easily though by using more negative feedback. As many of us have heard though, this can make for a product that measures better but sounds worse.

What got me to thinking about this was the fact that i purchased an old amp to run the subwoofer i just finished modifying for my Father. This amp is internally bridged, which means that there are actually four mono amps making up the two stereo channels. This provides twice the voltage potential, making for a pretty potent amp in what is a pretty compact chassis. This type of approach shares similar design strategy to balanced operation, which is what got me thinking about the potential for internal imbalances.

As to El's comments, most of the Pro Sound reinforcement gear that accepts / works with balanced gear are simply using quad op-amps running in complimentary fashion. These cost next to nothing and one of these IC's can do both stereo channels. Most high end audio gear are using discrete components of ( hopefully )higher quality, making the parts count and cost of production measurably higher.

My thoughts are that balanced operation has the potential to work better, but like anything else, it has to be properly designed and implimented with good quality control. Otherwise, there's just more to go wrong. Sean
>

PS... Lower grade circuitry may benefit more from balanced operation than state of the art single ended designs. At least with balanced operation, you've got some form of internal "checks and balances" without having to resort to GOBS of negative feedback.
albertporter's avatar
albertporter
4,949 posts
 
I prefer single ended interconnect for my 38 foot run between my balanced preamp to amplifiers.

My turntable looks to be running balanced from the appearance of the cable. I had a custom built balanced cable terminated as single ended. The purpose of this was to obtain the superior cryo treated balanced locking connectors for use in a tight, high stress situation.

Between the two (true balanced) Aesthetix pieces, there was some sonic gain with balanced runs, provided identical quality cable was used in each test. I concluded that cable design, shielding and termination were at least as important as the differences between SE and balanced.

In extremely long runs such as microphone cable the results would likely be very different. In some situations microphone cable is over a hundred feet and in proximity to electrical connections, sound reinforcement equipment, other signal cables and possibly television and computer gear. In this difficult situation, a true 600 ohm balanced has advantages and is the reason pro gear is set up this way.
twl
3,251 posts
 
Herman, I'm glad you took the time to write this post. I have made numerous short comments on the Single-Ended vs. Balanced issue, and I generally agree with you.

However, I think it is more of an issue of what people think, that is flawed, than the flaw of the cables themselves. Balanced cables are what they are, which is a design borrowed from pro audio to keep external noise lower on long runs of cable. The problem is that consumers have begun to get the notion that balanced is the better technology because it has "pro" applications, and looks "heavy duty". It strikes me as rather ironic, since most "pro audio" gear is generally not considered fit for home audiophile use.

And as far as the often quoted 6db gain increase is concerned, it is the result of the step-up transformers on each end of the line driver circuit that is providing this, and not the balanced cable. These line drivers are there to provide the extra "kick" needed for long cable runs that are expected with balanced lines. But these transformers also place additional parts in the circuit path that have signal losses and phase-shift associated with them. These are not present in the Single-Ended connections.

Just like with anything else, you have to use technologies where they are most applicable, and not generalize. For home use, my opinion is that Single-Ended is most often the right choice, unless the entire topology of the amplification chain is true balanced.
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