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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
eldartford
4,262 posts
 
Sean...I know how you feel about Op amps. I halfway agree with you on this subject, but only because Op amps are so often used in unsuitable applications. However, a unity gain buffer (which you need two of for a balanced line output) is an application wheren the Op amp is entirely satisfactory, and use of discrete circuitry would be a waste of money, and probably yield inferior performance.

I have done a lot of amplifier "bridging" before that term was coined, in particular as a way to drive a center speaker from a stereo amp by inverting one channel's signal. It seems to me that an amp in bridged mode would exhibit many of the advantages cited for balanced lines, yet it is commonly reported that amps in bridged mode don't sound so hot.

Finally (?) why do the two sides of a balanced line need to be matched? The whole idea is that the signal is floating, and can be received with a differential input amp that rejects common mode noise. If you ground one side of a balanced line (the extereme case), I think that you just revert to single ended.
ttathompaolcom
41 posts
 
the SMARTEST post ever...thank-you Herman!!!!!!
jjwinterberg
45 posts
 
My system doubles for both stereo and multi-channel playback and I have enough cables in the back of my rack that without balanced interconnects I do get common-mode noise. Maybe with better cable routing I would eleminate the problems but I just don't have the room.

JW
eldartford
4,262 posts
 
Jjwinterberg...Try grounding and ungrounding the various pieces of equipment. Ground loops are more likely to cause hum than pickup in interconnects. If your interconnects don't run alongside 115vac power lines, thay probably are not your problem.
russ_l
95 posts
 
Herman- I read your post several times but I fail to see what point you are (attempting) to make. Plus, you make many wrong assumptions. For example:

1- A balanced amp will not necessarily be twice as expensive as a single ended amp, and typically will be far from twice as expensive, as the cost of a typical high-end balanced amp (Jeff Rowland, Krell, Mark Levinson, BAT, etc.) is driven by the cost of the mechanical parts (the solidly damped chassis, the fancy front panel machining, the front panel display and controls, etc.) and not the parts on the circuit boards or the output devices.

2- The two halves of the amplifier can be close too or exactly perfectly matched using many techniques (local feedback, resistor trimming, potentiometer adjustment, etc.). I’ll admit though, this does add expense.

3- A balanced amp may, or may not reduce the noise floor, but in general will provide an increase in S/N ratio, as the noise remains constant while the output signal doubles in amplitude. Higher S/N ratio is always better.

4- A balanced amp in some instances CAN reject spurious noise within the amplifier. For instance, the input power transformer is radiating EMI throughout the chassis. An equal amount, or almost amount of noise will get into both halves of the amp and thus be cancelled, or almost completely cancelled-out at the output of the amp.

5- Lastly, and this is my input, a COMPLETELY balanced system, from the source through the power amp, effectively does away with all the various problems that can arise from the difference in ground potential from box to box. That's exactly why Naim (their stated reason) uses DIN connectors for box-to-box connections. And of course, a DIN connector is just another form of a balanced connector.

If you do not wish to use balanced components (your point?) that is your prerogative. However, balanced components, particularly a fully balanced system, can afford many advantages over a single ended system. That does not mean the balanced system will sound better but that it has the ability to do so, particularly in a system where the units are plugged in all over the place.

And, as always, IMHO.

Russ
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