going balanced/symetrical - what benefits?

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Hi,

Having built a complete balanced active system, I would like to know more about the benefits of a symetrical driven speaker system.
Beginning from the EMU1212m to a symetrical active filter to a symetrical LM3886 amp.
I know, there's a theoretical chancelation of noise and distortion.... And it proves itself in reality - ind idle there's absolutely no noise to hear even with my ears at the speakers.

Anyone that has a link with some hardfacts for me?
 
Hi,
the noise reduction benefits of balanced only become evident when in the electrically noisy environment of commercial premises AND when long interconnects must go from stage/source to mixing desk to amps/speakers.
In the domestic environment balanced is generally noisier or no better than single ended/unbalanced.
The extra electronics/transformers of balanced often degrade the signal more than the better unbalanced systems.

When we come to surround sound and wifi/mobiles in the home where electrical noise AND long cables become more prevalent, then the advantage of balanced may just start to show through.

Doug Self, Rane, Jensen & Walt Jung could be useful sources.
 
This is what I have found yet:

The main advantages are:

*
Greater power supply immunity. Differential amplifiers present a constant load to the power supply, resulting in less noise in the power supply. Differential amplifiers also resist input (noise) from the power supply to a much greater degree.
*
Lower noise. Differential amplifiers have roughly 6 dB lower noise then the same circuit executed in a single-ended manner. This can be very important in moving-coil preamp sections.
*
Lower distortion. Differential amplifiers tend to cancel distortions that single-ended amplifiers cannot.
*
Drift is reduced by the tight coupling of the two halves of the amplifier. Performance over time is improved. N
*
oise rejection. Common-mode rejection ratio is the measurement of a differential amplifier's ability to not amplify noise that is common to both inputs. It is typically at least 55 dB, and can approach 140 dB in some critically-tuned designs.

There are also some disadvantages:

*
Increased cost. Differential amplification takes more parts to execute. For a given number of stages of gain, differential amplifiers have about 50% more parts.
*
Greater complexity. Although the number of stages of amplification remains the same for single-ended and differential amplifiers, differential amplifiers have more requirements to execute, for example, a negative-voltage power supply.


But I wanted some more deep explanations.

Just a thought: If I use a dual opamp, like the LM4766, to drive a Speaker in balanced mode, shouldn't this method not only reduce noise (because its a random signal it doesn't chancel out completely) and distortion also.
 
I don't think that those points are from a marketing department but more are more or less correct.

The way I understand, non balanced topologies can be made to perform extremly well and probably transparent to the human ear... or maybe not..?

The fully symmetrical and bridged/balanced topology do have greater potential regarding noise and distortion performance. The question is if or when that performance is needed.
Andrew touches that subject in his post.

But please give me something that beats the performance from this amplifier;


http://www.hardwareanalysis.com/content/article/1842.5/extrema-reference-class-a-diy-amplifier/

:)




/Peter
 
Symetrical input

In a symetrical input, when the signal goes positive in the plus input, has also to go negative in the negative input at the same time (180 deg.phase shift) for it to work.
So when an external noise (say a motorcicle sparkplug) enters the wire, it will be positive or negative in both wires at the same time (no phase shift) canceling each other.
 
As many have said ...

The benefit of a balanced link terminated in a differential stage is that it cancels common mode noise picked up by the link. It does nothing for differential mode noise or distortion.

The benefit of a balanced circuit operated with a balanced input signal and driving a balanced load is that it keeps the power supply out of the signal path.
 
Hi

If you want links with hard facts I would try the borbelly and pass diy web sites. The papers there go into considerable detail that may be what you are looking for.

Interestingly Borbelly believes in symmetrical and balanced architecture. Pass seems to have a liking for a simpler topology. I hope that I am not misrepresenting the views of either of the gentlemen as I have a high regard for both.

I think that what you are hearing is that a symmetrical acchitecture will provide a cleaner ( less distorted ) output. However there is a lot to be said for a very simple design with fewer parts which many believe delivers a "purer" sound..

As an example of this I have designed numerous loud speaker systems over the years with 1,2 and 3 drivers. I have tried first, second and fourth order crossovers. With a fourth order crossover it is possible to produce a very clean output curve. However I still prefer to listen to a directly connected mid range driver with a minimum of assistance in the base and treble from tweeters and subwoofers with simple one way crossovers on the tweeter and subwoofer only. The curves do not look as good as provided by a more complex crossover but I prefer the detail and smooth sound.

Others may disagree and I believe you have to find out for youself if you prefer simpler circuits or more complex ones. However I hope the two sites I mentioned above will help you.

Don
 
Balanced link

An unbalanced link will work fine, but if you use a balanced link you will have a signal to noise ratio with an increse of 6dB due to the higher gain you have in the wanted signal but not in the noise.
The noise floor or random noise produced by the audio signal source, will not have the 6dB increase gain as it is random and some times will have a phase shift and have a higher gain and some times will not have a phase shift canceling each other so no gain.
So at statisticly speaking, the noise floor will not have this increase of 6dB gain but will also not be canceled, having a gain of an unbalaced link. But the wanted audio signal will always be 180 deg. phase shifted and have 6dB more than an unbalanced link.
 
Balanced circuitry has no place in consumer audio. It is all BS.

Balanced audio has two benefits:

1) Reduced common mode noise in cables. This application is seen most commonly in microphone. Due to the low signal level and long cables, balanced/differential signaling has its place in audio recording and public addressing systems.

In consumer electronics the interconnect cables are short (less than 2 m), well shielded and the signal levels are considerably larger than microphone signals. Unless of course you have the CD player at one end of the room and the preamp or amplifier at the other end, but why would you do such a thing?

Common mode noise cancellation only works if the two differential signals are kept close together. In differential cables the wires are twisted together to provide a tight coupling. Having them apart as in differential electronics defeats the purpose.

2) Balanced signaling quadruples the output power of amplifiers because of the doubling of voltage. But what good is power if it does not have the current capability? It's like a Ferrari running on bicycle tires. I question the need for such power anyway. Who needs a 1000 watt amplifier? We are talking about consumer audio here not professional audio.

Here are the cons of differential signaling/electronics:

1) Increased noise. We have two sets of electronic circuits working in differential mode. This doubles the random thermal noise in the circuit. Differential amplification sums the two signals and we get double the noise. I used to have a power amplifier from a highly reputed company which has a mono switch. In mono mode the background noise was considerable higher. I am not surprise if it went up by 6dB but I have no way to confirm it.

2) Increased distortion. Phase difference between the + and - signals results in signal distortion. No electronic is perfect or perfectly symmetrical. One signal will arrive later or earlier than the other. And the sum of it is distortion! And talking about distortion.....Each set of electronic introduces its own set of asymmetrical distortion and the sum of it is double the distortion!

3) More expensive and complicated electronics. Why pay more for no added benefit?

Balanced audio supporter argue that the greatest benefit is the cancellation of symmetrical nonlinearity. The argument is that the + and - circuitry will produce distortion that is symmetrical so the sum of it is the cancellation of the distortion. The way I see it, the benefit is negligible because the THD of modern audio circuitry is already very good. Can you tell the difference in distortion between 0.01% and 0.001%? Tube amps are no where close to this anyway and they can sound good but this is another topic on its own.

There are some companies that swear by it like Ayre and Balanced Audio. McCormack DNA-500 and the McIntosh MC1201 are balanced amplifiers. Yes they sound good but you pay for extra circuitry that you don't need. I believe in the KISS philosophy: Keep It Simple Stupid!
 
Balanced is about equal impedances to ground, not equal signal levels. Signal levels have nothing to do with balanced. Equal impedances help cancel common mode noise, not signal.

Equal impedance to ground does not require double the circuitry.

If balancing is done with transformers, you can break the ground connection between components. The complete and utter elimination of hum is a definite benefit.
 
Balanced circuitry has no place in consumer audio. It is all BS.

Hey, Ceasar-
If you are ever in New Jersey, stop by my house. You can listen to the noise that comes through the ground with single-ended circuitry. It can be clearly heard from my listening chair.
With true balanced circuitry, poof, noise is only audible about 5 inches from the speaker.




Common mode noise cancellation only works if the two differential signals are kept close together. In differential cables the wires are twisted together to provide a tight coupling. Having them apart as in differential electronics defeats the purpose.

Actually, I disagree. The true noise reduction occurs when the common signal (ie ground noise) is fed to a differential pair. The noise simply can't be amplified. Take a look at the Son of Zen article by Nelson Pass for a good explanation of the mechanism that causes this. It took quite a while before it 'clicked' in my head, but once you see it, it is clear.:)

JJ
 
jupiterjune said:
Actually, I disagree. The true noise reduction occurs when the common signal (ie ground noise) is fed to a differential pair. The noise simply can't be amplified.

Well, I don't think it's too far a stretch to say that reducing the amount of noise that's picked up in the first place should be considered "noise reduction."

I mean, you've really got two things going on here. You've got the cables where the noise would be picked up and then you've got the differential input which rejects what noise is picked up. Even if you have a great differential input, its performance can only be compromised if you're not doing what you can to reduce the amount of noise that's picked up in the first place.

se
 
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jupiterjune said:

...You can listen to the noise that comes through the ground with single-ended circuitry.


caesar148 said:

2) Increased distortion. Phase difference between the + and - signals results in signal distortion. No electronic is perfect or perfectly symmetrical. One signal will arrive later or earlier than the other. And the sum of it is distortion! And talking about distortion.....Each set of electronic introduces its own set of asymmetrical distortion and the sum of it is double the distortion!


Both balanced and unbalanced topologies have their advantages and disadvantages. Within a professional environment there may be no option, however within a domestic environment it is different and there is a clear choice. Ultimately there are key deciding factors in your choice, and these keys have been noted by jupiterjune and caesar as shown above.

With unbalanced design the key factor is the dependance on a signal referenced to ground. In many situations / installations the 'ground quality' can be very poor, as alluded to by jupiterjune, and this can lead to noise, hum-loops and dynamic distortions not measurable under static / laboratory conditions. The more ground circuits that are connected together, the worse it is likely to be.

With balanced design the key factor is the dependance upon exactly matched positive and negative phases, which calls for precisely matched electronics. If the phases are not matched, as noted by caesar, the signal will simply be distorted away from the original. Personally I believe that this is one of the reasons why much commercial domestic equipment sounds poor when used in balanced mode... the commercial constraints of the design do not allow for precisely mathed + / - phases and hence the signal is not faithful to the original.

So when you consider the question of balanced vs unbalanced in a domestic environment think hard about precisely matching + / - phases for balanced circuits, and optimising your ground distribution for unbalanced working.
 
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