What does ‘balance preamp’ mean?

Please read up on this article, 

https://www.stereophile.com/features/335/index.html

ARC Ref 6 SE is a fully-balanced, Class-A design with zero feedback 😊

You're missing a -d.

Many if not all components have power supply sections with a large massive transformer usually off to one side. Especially true of preamps because designers like to keep these noisy parts away from the sensitive circuits handling the signal. Not so critical with stock factory feet but many audiophiles add springs or cones. With these its critically important to balance preamp so it doesn’t tip over.

Yes BIG DEAL.

Very big deal. Not for the small minded.

So basically it makes no diff if balanced or unbalanced.  Marketing hype.

No, a real balanced circuit is one where the positive (+), the negative (-) have distinct circuits, and negative is distinct from earth.So there is a higher manufacturing cost. There is also noise cancellation -- i.e. any noise common in both circuits is cancelled out --  hence, balanced is used in professional audio applications which are noisy environments.
For home applications, some content that balanced sounds better, others that single ended does -- as usual.

Given your many posts I believe you would benefit from the purchase of Robert Harley's book 'The Complete Guide to High End Audio'.  Money well spent. 

No, a real balanced circuit is one where the positive (+), the negative (-) have distinct circuits, and negative is distinct from earth.So there is a higher manufacturing cost. There is also noise cancellation -- i.e. any noise common in both circuits is cancelled out -- hence, balanced is used in professional audio applications which are noisy environments.

^^ This. Its not hype- just better technology.

Given your many posts I believe you would benefit from the purchase of Robert Harley’s book ’The Complete Guide to High End Audio’. Money well spent.

THISSSSS!!!!!!!!!!!^^^^^^^^^^^!!!!!!!!Only don't just buy it- READ IT!

So what is a balanced vs unbalance preamp?
difference?

Unbalanced units are always on the verge of tipping over. They also require inordinate amount of aftermarket thingies for them to perform at their best.

" So what is a balanced vs unbalance preamp?"


Purchase and read Chapter 7 - Preamplifiers - of Robert Harley's Introductory Guide to High Performance Audio Systems

Seriously. Get the book. Read the book. STUDY the book. The whole book. Unbelievable what you will learn. Introductory is newer than Complete, but there are current updated editions of both so you cannot go wrong.

Ok, but seriously, what’s the answer?

GregM answered this fairly well above, but I'll try to add some more background and detail.

In most home audio systems, the analog signal between devices (e.g. from your dac to your preamp, or preamp to amp) uses an RCA cable. This type of cable has a single signal conductor and a ground conductor. The ground conductor is doing double duty here, providing both a ground reference between devices, and providing a return path for the audio signal.

In a balanced system, a balanced cable using XLR connectors is used to connect devices. These cables have two conductors for carrying the audio signal, and a separate ground conductor (often the shield). In this case, the audio return current does not have to share the same conductor as the ground connection, and any ground currents that may exist will not interfere with the audio signals. Ground currents might occur if, for example, the two devices that you are connecting are plugged into different outlets, or if one or more of the devices being connected has a poorly implemented grounding system.

The other potentially big advantage of balanced connections is their improved immunity to noise pickup, but this is dependent on properly implemented differential inputs.

It's possible to use balanced connections without using a balanced preamp, but the signals have to be converted back and forth between balanced and single-ended (meaning a single audio circuit path). I suspect that most home audio devices that have XLR connectors to support balanced connections work this way. 

This can still have advantages in that ground problems are reduced and most of the noise picked up by the interconnect cable can be cancelled (assuming a properly implemented differential receiver on the device inputs). But it also adds extra circuitry that would not be required with normal RCA connections. So unless you have a noisy electrical environment (live near a radio transmitter, cell tower, etc.), RCA connections may be preferable. 

A "real" balanced preamp has separate circuits to handle the two audio phases, so they don't convert the signals from balanced to single-ended and back again. This generally eliminates the unnecessary circuitry to convert back and forth, and also has the advantage of improving the signal to noise ratio and potentially cancelling some non-linear distortion products. The downside is that virtually all the audio circuitry in the preamp is doubled which will significantly increase the cost. 

Personally, I'm a fan of fully balanced systems because of their improved noise performance, but they aren't for everyone. 

An additional advantage of balanced preamps is that they have improved immunity to noise in the power supplies of the preamp. This is because any such noise is common to both phases of the signal and so it less able to be amplified as opposed to a single-ended circuit.