I am actually in the middle of writing an article on a blog, which will include the NuForce HA-200's (x2).
However, here is a sort of extract/some info about balanced audio from my article (this is very much condensed and not meant to be in-depth).
First, when we talk about stereo, we mean Left and Right channels. Specifically: Left Negative, Left Positive, Right Negative, and Right Positive. This is known as polarity, and each channel has a phase, positive and negative. (For sake of clarity lets define each polarity as L+, L-, R+, and R-).
To make a stereo amplifier, you need to address each phase. Without going into all of the numerous topologies on how this is done, lets just assume that a stereo amplifier will amplify each phase of each signal.
So, this then brings us to two ideas of amplification, single-ended (SE) and balanced:
In the most general cases, most stereo amps amplify by bridging the incoming L+ and L- phases together, amplifying both phases simultaneously, and ditto R+ and R-. The connections, input and output, share a ground signal (wire) in the cables itself and in the circuitry. (That is to say that the L and R channels share the same ground wire).
This means that most stereo amps will have a design that amplifies the left and right channels almost simultaneously, but technically are internally split as L+/L- and R+/R-.
In the audio world, this is collectively known as a single-ended design, and is often a one-box solution.
Now, you can have SE designs in which there is one amplifier powering left and right channels together, two amps for each channel, or, uncommon, one amplifier per phase of per channel. However, due to the grounding of these amp designs, they are still single-ended. The latter two, more extreme, designs are considered to be the more superior but it is not often seen in SE amps. It is, however, popular in balanced designs.
The next up from SE designs in stereo amplifiers is, first, that the circuitry design has grounding per each channel, not combined. That is true of the I/O, and the balanced cabling, where the left and right channels have completely separate ground wire per channel, all the way to the termination (2.5mm TRRS, 4-Pin XLR, 2x 3-Pin XLR, 4.4mm TRRS Pentacon, etc). This is the first BIG difference between SE and balanced amps, and why special cabling is needed*.
From here, you have two popular balanced amp topologies:
- Bridge-Tied Load/Bridged Transformerless:
Here you have two amplifiers, where one amp is fed L+ and R+ but receive the phases completely separately. Ditto the second amp which receives the alternative signals, L- and R-, again, having the incoming inverted phases separately.
This is, technically, a superior design as each amp has a job to do and crosstalk and noise between channels is lowered.
This design typically has the advantage of doubling voltage and swing (electrically), meaning more power which should be read as 'this amplifier has more headroom to play music at different loads'; ie better at playing the nuances, varying volume differences, and changes in a piece of music.
These designs are usually found in one-box solutions.
- Fully differential balanced:
This is the cool balanced design, and is what 2x HA-200's can do.
Similar to BTL, but here there are four amps dedicated to each phase of each channel. Each amp receives each phase separately too. Thus:
One box for Left channel: 1x amp for L+, 1x amp for L-
One box for Right channel: 1x amp for R+, 1x amp for R-
Though technically this is also doubling voltage and swing, it can be seen as quadrupling depending on amp design. However the magic here is that because each phase is being treated individually, even more noise and channel crosstalk is reduced, more so than BTL (again, depends on the design).
Such amps can also be found in one-box solutions but they are very large, but it is more common to see them in two-box designs, the latter being referred to as monoblock amps (one box is for L, the other R). (Some crazy amp designs will have a four box solution too).
Do NOT modify or use adpaters on SE cables into balanced; you WILL damage or short your equipment. That is because SE wires share a ground wire.
Balanced cables do not, so can be used in balanced gear, and with adapters SE gear too, without worry.
Lets relate this to the HA-200.
One HA-200 has two internal amps inside. In SE mode, each amp is bridged, hence normal stereo mode.
However, the amp circuitry allows SE ground cables and balanced cables (how is too much for writing here, but is itself an interesting read and topic).
When you get two HA-200's and use balanced inputs and output cables, the two internal amps per box are no longer bridged; they are treated as each individual amp, dedicated to each phase of each channel.
What makes the HA-200's special is that it includes two design topologies per box, and when you have two boxes you have the only monoblock, fully differential amp system that is cheaper than any alternative on the market, with loads of power.
It is this that makes the NuForce HA-200 interesting.
Hope that this makes sense and helps ^^