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Old 13th September 2008, 01:05 AM   #1
kanifee is offline kanifee  United Kingdom
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Default balanced input/output q's

Well im pretty new to hifi and have been wondering for a while just what is the difference between balanced output and standard output, what benefits does balanced output have and to implement them does the hole system have to run on balanced inputs outputs to utilize it?
Lastly can you use balanced inputs/outputs on a device that doesnt natively support it?
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Old 13th September 2008, 10:28 AM   #2
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Unbalanced signals use the ground for the return signal.

Balanced signals do not. The signal is copied and inverted. The non-inverted signal and the inverted one have a wire each and the ground has another one, which is usually the shield. At the end of the chain the inverted signal is returned to the non-inverted state again and added to the original non-inverted signal. This is often done before the power amplifier, but may as well be skipped by simply using a bridged amplifier.
Advantages are
a) since the ground is not used as return signal path there is usually no trouble with hum loops.
b) distortion signals, e. g. from inductive coupling into the wires cancel each other out, because they influence the inverted and the non-inverted signal correspondingly.
Disadvantages are
a) higher component count
b) more expensive
c) compatibility issues, because home audio equipment is most of the time unbalanced. One might have to use professional audio equipment that is usually balanced or one of the few balanced home audio components that usually come with a big price tag.

The whole system does not have to be balanced, but it makes of course more sense to have it either entirely balanced or entirely unbalanced.

And yes, you can use balanced in-/outputs on unbalanced devices. Adapters are available and buffers that convert unbalanced to balanced or the other way round are available and can also be found in this forum.
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Old 13th September 2008, 12:59 PM   #3
kanifee is offline kanifee  United Kingdom
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Sweet, i plan to use a bridged amp so this is a necessity yes?
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Old 13th September 2008, 02:27 PM   #4
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Not a necessity, but convenient. You can use two identical non-inverting set-ups and feed one with the inverted signal and the other with the non-inverted one.

If you go unbalanced into a bridged amp you have two possibilities. Use an inverting and a non-inverting set-up (= two different PCBs) and don't forget that the feedback resistors have to be different. Or use identical non-inverting set-ups and add an unbalanced-to-balanced converter.

On the other hand, if you go balanced into a standard non-bridged amp, you can use the inverting input for the inverted signal and the non-inverting input for the non-inverting signal.
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Old 14th September 2008, 10:05 AM   #5
kanifee is offline kanifee  United Kingdom
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Ok i think im getting to grips with it, how though do you deal with source selection with a balanced setup, or would you convert the signal to unbalanced before selection and then back to balanced afterwords or is so much conversion a bad idea?
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Old 14th September 2008, 10:34 AM   #6
lineup is offline lineup  Sweden
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a good advice
when dealing with BALANCED Signals or XLR Music electronics:

Use some good IC to Drive and Receive your signal
Most used and fair price dedicated special chips for this are:
---------------------------------------------
Analog Devices:
SSM2142 and SSM2141 ... driver & receiver
http://www.analog.com/en/audiovideo-...s/product.html
http://www.analog.com/en/audiovideo-...s/product.html

Burr-Brown/Texas Instruments:
DRV134 and INA134 ... driver & receiver
http://focus.ti.com/docs/prod/folders/print/drv134.html
http://focus.ti.com/docs/prod/folders/print/ina134.html
---------------------------------------------


Why do I give this advice.
It is based on my own knowledge from other peoples audio projects
and use of balamnced configusration to send receive Hi-fi Audio Signals.
And the Conclusion these clever people have told, everyone of them is:
Use some precision Special IC .. that can do this .. and do this well.

May seem like very easy just use one 'opamp' and use one inverted and one non-inverted.
But in this case Easy not very often = Good.
You have to be something like as clever as John Curl. The very experienced, old and famous amplifier designer,
in order to get those levels of quality that one low priced chip can give you right away.

In the end.
It is your Chip Amp, your goal, your requirements that will count.
And if you are after good audio, you take my advice ..
if you are not bother with have some less good, or even bad audio
you just forget my advice

What I should do, with all this my long experience in Audio .. ???
Even me, would go for Burr-Brown DRV134 .. INA134 special IC:s for Balanced signals.
If I was to make my balanced audio system.

Lineup
__________________
lineup
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Old 14th September 2008, 07:29 PM   #7
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Quote:
Originally posted by kanifee
Ok i think im getting to grips with it, how though do you deal with source selection with a balanced setup, or would you convert the signal to unbalanced before selection and then back to balanced afterwords or is so much conversion a bad idea?
In PA systems it seems to be quite common to unbalance at a mixers input, do the signal processing, and rebalance again at the output. Then again in a mixer there are usually dozens of op amps, so a few more or less won't make such a difference.

A complete balanced set-up would mean to use a selector with 4 poles per source, and a 4-channel volume pot.

If you go the unbalance-before-selector-and-pot-and-then-balance-again-path, you will need two converters from unbalanced to balanced at each stereo source, another two converters from balanced to unbalanced per source at the preamp input and another two from unbalanced to balanced at the preamp output.

You might be better off buying a small professional mixer, where everything you need is already inside, and they can be surprisingly cheap. I. e. if you don't mind to use faders instead of a selector.
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