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-   -   going balanced/symetrical - what benefits? (http://www.diyaudio.com/forums/solid-state/109862-going-balanced-symetrical-what-benefits.html)

weissi 10th October 2007 10:46 PM

going balanced/symetrical - what benefits?
 
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?

AndrewT 11th October 2007 12:02 PM

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.

weissi 11th October 2007 03:03 PM

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.

AndrewT 11th October 2007 03:45 PM

Hi,
I think most of your list of advantages is wrong or misleading.
It reads more like a bit of advertising from a supplier who has tried to invent (spurious - arguable) reasons for his balanced design.

Pan 11th October 2007 05:55 PM

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/cont...diy-amplifier/

:)




/Peter

Michael-Rifa 11th October 2007 11:25 PM

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.

Werner 12th October 2007 12:15 PM

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.

Pan 12th October 2007 12:37 PM

One more thing..reduction/cancellation of asymmetrical nonlinearities.

There's only one slight drawback the way I see it and it's the higher cost on parts.


/Peter

AMV8 12th October 2007 04:54 PM

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

Michael-Rifa 13th October 2007 06:30 AM

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.


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