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Old 21st January 2009, 09:49 PM   #1
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Default Balanced (preamp) Outputs - Why ?

I would like to know what advantages (if any) are there to using "balanced" outputs from a preamp? Better sound? stability? How much of this is theory and how much real world fact? I've seen where preamps like Quad99 have a ribbon cable interface between amp - preamp (balanced) as well as standard RCA i/o. Some listeners report better sound through RCA over "quad-link" balanced connection. What's the scoop ?
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Old 21st January 2009, 10:06 PM   #2
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Balanced lines are advantageous *only* in electrically noisy envirionments, particularly if the line is long.

Balanced operation's sole purpose is to reject noise picked up by the cable .

The balanced input/output circuitry is more complex and costly, so is sometimes poorly implemented - to avoid increasing the overall cost substantially. In that case, the RCA unbalanced connection can sound better.

Ribbon cables are not good for noise rejection so invariably require the use of balanced signalling. Unless they are really short, and protected from noise by the metal cabinets, etc.
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Old 21st January 2009, 11:04 PM   #3
fotios is offline fotios  Greece
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Although Steerpike's reply covers your query, the important thing there is in the balanced inputs of amplifiers. Because these composed from subtracter circuits which converts the balanced signal to single ended, the gain (or headroom for proffesional audio) it is doubled usually in comparisson with RCA inputs. Nothing less or more.
This signal proccess it is borowed in domestic audio from pro audio.

Fotios
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Old 21st January 2009, 11:30 PM   #4
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Default Balanced I /O

Is the balanced i/o essentially then a differential input to reduce
or reject ( common mode) noise ?
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Old 21st January 2009, 11:37 PM   #5
lgreen is offline lgreen  United States
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Default A little more

The above posts are correct, note that a blanced output does little good if the thing it is going into does not take the difference of the balanced signals, i.e., if it just discards the negative signal for example.


Think about it a little more. Anything that is truely balanced will typically accept a balanced connection, operate on the signals in a balanced manner, and provide a balanced output. Thus all common mode noise on the input wire, all common mode noise added by the balanced circuit itself, and all common mode noise on the output wires will be canceled/ rejected.

Chain together a balanced CD player or differential DAC, balanced preamp (BOSOZ) and balanced amplifier (Aleph X) and you get a beneficial reduction in noise that carries through from component to component.

That said, most people will use a balanced cable from source to preamp or preamp to amp where there are very long cable runs (like microphone to preamp in a church) as all common noise picked up by the cables are canceled.

EDIT- looks like I was typing when you posted above- answer is yes, but also if the preamp circuit itself is balanced you will reject the common mode noise added by the preamplifier circuitry.
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Old 24th January 2009, 05:15 AM   #6
sardonx is offline sardonx  Canada
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Correct me if I'm wrong but balanced lines are immune to ground and external noise, so in my eyes yeah that's better sound, or at least an improvement in design. You may not need it, but by going fully balanced throughout the chain you're making sure you are eliminating those (potential) problems. Whether you like that sorta reassurance in your audio system or not is up to you.
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Old 24th January 2009, 05:25 AM   #7
SQLGuy is offline SQLGuy  United States
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Quote:
Originally posted by fotios
Although Steerpike's reply covers your query, the important thing there is in the balanced inputs of amplifiers. Because these composed from subtracter circuits which converts the balanced signal to single ended, the gain (or headroom for proffesional audio) it is doubled usually in comparisson with RCA inputs. Nothing less or more.
This signal proccess it is borowed in domestic audio from pro audio.

Fotios

There are also a few amps that are differential throughout. The amp I use for mids/highs in my system is one: a SUMO Andromeda II. It's actually two complete amplifiers per channel with the output taken differentially between them, like a bridged amp.

I suppose you could also use the balanced output from a preamp to drive both channels of a stereo amp and bridge it that way, though most amps lose performance in bridged mode (albeit while gaining power into higher impedances).

And, I suppose, it's arguable that if the whole playback system, from CD DAC, through preamp, through amp, to speakers were balanced, you could gain a lot in terms of S/N and immunity to power line noise and ambient EMI/RFI. Double the parts, though!

Once I'm done repairing the PS Audio, my next project is to convert my DCX2496 to maintain a balanced signal end-to-end, since most of the internal circuitry supports it anyway.
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Old 24th January 2009, 08:47 AM   #8
fotios is offline fotios  Greece
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Quote:
Originally posted by SQLGuy



There are also a few amps that are differential throughout. The amp I use for mids/highs in my system is one: a SUMO Andromeda II. It's actually two complete amplifiers per channel with the output taken differentially between them, like a bridged amp.

I suppose you could also use the balanced output from a preamp to drive both channels of a stereo amp and bridge it that way, though most amps lose performance in bridged mode (albeit while gaining power into higher impedances).

And, I suppose, it's arguable that if the whole playback system, from CD DAC, through preamp, through amp, to speakers were balanced, you could gain a lot in terms of S/N and immunity to power line noise and ambient EMI/RFI. Double the parts, though!

Once I'm done repairing the PS Audio, my next project is to convert my DCX2496 to maintain a balanced signal end-to-end, since most of the internal circuitry supports it anyway.
If i remember well, one expertised member told me that this amp architecture is named horizontal push-pull. I think also that N. Pass he uses a full balanced topology in his products. The thing is quite simple... you take the balanced outputs of the source, and you drive them in four seperate input buffers inside the preamplifier (two for left and two for right)... and for volume control you are using a four gang potentiometer before the four output buffers. With this way you can avoid the successive convertions from balanced to single ended if you are using a usual stereo pot and vice-versa after the pot. Also, you can build with a four gang potentiometer (of big precision) a nice passive preamplifier fully balanced from input to output.

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Fotios
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Old 24th January 2009, 08:59 AM   #9
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In my opinion the biggest advantage of balanced in domestic audio is that it removes the ground (system, mains) from the signal path.
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Old 24th January 2009, 10:44 AM   #10
EUVL is offline EUVL  Europe
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While the above are all truth, there are a couple of points that are often forgotten :

1) Perfectly matched balanced amplifiers will have self-cancellation of even-order harmonic distortions, with only odd harmonics remaining. This changes the characteristics of the "sound". Pls consult the Pass Lab forum for previous comments from Nelson Pass on second vs third harmonics.

2) Fully-balanced Class A amplifiers will draw (near) constant current from the power supply as long as they stay in the Class A regime, thus making power supply design less critical.

And of course with the ground now only acting as a reference and not carrying current (see previous post), it also becomes less critical.

To make the most of the balanced cofiguration, one should really implement fully balanced circuits from start to finish (e.g. from DAC output to power amp output).


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