Balanced Inputs? Is it Needed?

[Rolyasm]

I see a lot of amps/receivers that don't have balanced inputs. I realize that I don't necessarily need this to have a good system, but if I was choosing 2 similar amps, one with and the other without the inputs, should I lean more towards the one amp just because of the balanced inputs, all other specs being about equal? Does the balanced inputs really sound that much better? Also, if my amp has the inputs, I suppose my pre/pro would also need the same? Or can I use the a different input/ouput connector? So logically, if my other components didn't even have the balanced inputs, it would be futile to buy an amp with balanced because I couldn't use them anyway? Right? Just trying to get this all straight in my head.
Roly

[Andrew M Ward]

Question 1) should I lean more towards the one amp just because of the balanced inputs, all other specs being about equal?

Question 2) Does the balanced inputs really sound that much better?

Also, if my amp has the inputs, I suppose my pre/pro would also need the same?

Roly

1) You should consider a balanced preamplifier if it has a true balanced topology. However I would conservatively guess that 90% of gear with balanced inputs are simply providing an input and quickly converting that balanced signal to a single ended signal as it reaches the board. Advantage = zero … why do they do this? True Balanced topologies are really expensive and present a whole series of different problems for the manufacturer.

2) You will notice a 6dB gain which can mask the noise floor (that’s a good thing) but really your advantage comes in (in my opinion) only in that you'll be using a fine cable (XLR) that is fantastic at resisting interference and can make super long runs with lower signal loss.

3) Balanced (in my opinion) only provides a real advantage if the topologies are balanced on all pieces and all the pieces are connected using balanced interconnects. otherwise (I suggest) saving your money on other cool stuff like more CD's or higher end single ended cables.... Just a thought.

[Andrew M Ward]

The Expense Associated with Balanced Design Topology

in response to a private message:


Balanced circuits (also called differential or symmetrical) provide a means for rejecting noise and distortion whenever it appears identically on two different signals.

For this reason, balanced components and interconnects are designed to handle two separate signal paths per channel. One is an inverted or mirror image of the other. When applied to a differential amplifier, the signals are subtracted, one from the other. The result is that noise and distortion that are the same on both signals (common mode) get subtracted away.

The signals that are opposites of one another would add to zero if they were being added together, but since they are being subtracted, they produce a larger, clean copy that is twice the size of the original, (hence the 6dB gain) minus anything that was the same on both signals.

The signal is now larger compared with the noise (improved dynamic range) and noise and distortion common to both paths have been largely eliminated. When well-executed, balanced signal paths may significantly outperform the standard single-ended variety.

All signals, once in the balanced mode, (if done correctly in my opinion) are routed through a DC servo to remove any unwanted DC from the source. (more expense) Coupling the signal in this way eliminates the need for sonically degrading DC blocking caps, while protecting speakers from the possible damage or distortion resulting from passing DC through to the amplifier.

True balanced (differential) power amplifier topologies don't pass DC when in a critical mode, which is why you see pseudo high-end amplifiers passing DC (the big K) amplifiers are constantly destroying speakers by "going DC".

For balanced signals a further benefit applies in a well made design.

Any small imbalance caused by the volume control is eliminated by the configuration of the differential output buffers. Keeping in mind that the balanced output buffers consist of four identical circuits, two are employed as a differential buffer amplifier for the inverted signal and two for the non-inverted.

The balanced output of the volume control drives both + and - sides of the inverted path, then with polarity reversed, drives the - and + sides of the non-inverted path. This topology assures optimum common mode rejection for amplitude errors as well as any other common mode noise or distortion artifacts.

even trick-er and more expensive and done correctly...

The topology of each output buffer is executed with discrete components. Low-noise J-FETs are utilized at the inputs, gain is provided by second-stage bipolar transistors and the MOSFETs are used at the output to isolate the load from the bipolar gain stage.

J-FET's where they work best
bipolar where they work best
MOSFET's where they work best

sounds easy right?
Andrew M Ward

[aud19]

1) You should consider a balanced preamplifier if it has a true balanced topology. However I would conservatively guess that 90% of gear with balanced inputs are simply providing an input and quickly converting that balanced signal to a single ended signal as it reaches the board. Advantage = zero … why do they do this? True Balanced topologies are really expensive and present a whole series of different problems for the manufacturer.

2) You will notice a 6dB gain which can mask the noise floor (that’s a good thing) but really your advantage comes in (in my opinion) only in that you'll be using a fine cable (XLR) that is fantastic at resisting interference and can make super long runs with lower signal loss.

3) Balanced (in my opinion) only provides a real advantage if the topologies are balanced on all pieces and all the pieces are connected using balanced interconnects. otherwise (I suggest) saving your money on other cool stuff like more CD's or higher end single ended cables.... Just a thought.

Pretty much what I was going to say