[Keith says, using his God-like powers to interject:]
That's not actually true...
More accurately... they're making assumptions that are usually, but not always, true.
More specifically... they're making a generalization that is almost always true for modern equipment.
Lots of vintage balanced gear worked just fine with only a two-wire connection.
It is fair to say that "virtually all modern equipment with a balanced input or output requires and expects a three wire cable".
(Which includes two signal leads and a ground connection.)
When applied to a signal the term "balanced" refers to the fact that it consists of two equal-but-out-of-phase copies.
With a balanced interconnect the overall signal is the difference of the signals on the two wires.
So, to get back the signal, you subtract the signal on the two wires.
This works out especially well since any noise that is picked up will usually be common to both wires.
So, when you subtract them, the signal is doubled, but the noise cancels out.
With a balanced amplifier the two equal-but-out-of-phase copies are amplified by two identical amplifier channels.
Then, when you connect the speaker across their outputs, the current through the speaker is again the difference of the two signals.
Unlike with wires, the noise created by amplifiers is mostly random, so the noise doesn't cancel out much.
However, we can expect and distortion to be similar in both amplifier channels, and so THAT largely cancels out.
So the result is a cleaner signal with less distortion.
(Not all types of distortion cancel out - but enough of it does to make a difference.)
The distinction that involves that third wire is that most modern equipment uses an actively driven connection...
And actively driven connections generally insist on having some sort of ground reference... which is what that third wire provides.
A speaker is "a two wire device" - which means that, technically, it is not balanced, but floating (in this context they are the same).
The current that goes through the speaker ONLY depends on the difference between the voltage at its two terminals.
It doesn't matter whether one of those terminals happens to be grounded or not.
Likewise, with a passive dynamic microphone, and a preamp with a TRANSFORMER COUPLED input, you don't need a ground either.
All that matters is the difference between the two wires carrying the signal.
And, yes, there are transformers that only use two wires on their input.
There are various reasons why, in some designs, a ground connection may be beneficial, or even required.
Since no balanced input is perfect, none is perfectly immune to noise, so a grounded shield which reduces noise is still useful.
And some circuits require a physical ground reference for various other reasons.
(Some transformers ground the center of the input tap; others may connect the shield of the transformer to ground.)
Many years ago I owned a very low output ribbon microphone - which had a passive balanced connection...
I also owned a vintage microphone preamp - which included true balanced transformer coupled inputs...
They worked together just fine, with almost perfect noise immunity, even when connected together using plain old two wire unshielded lamp cord.
However, with most modern gear, even though the two signal leads carry two identical equal-and-out-of-phase signals...
Each of the individual signals is referenced to ground.
(Basically you have two unbalanced signals that TOGETHER comprise a balanced signal.)
The reason is that there are active amplifier circuits at both ends of the connection - and THEY require the ground connection.
(You could technically avoid that ground wire - but only if you could guarantee that the devices at either end shared EXACTLY the same ground.)
In fact, some modern microphone preamps will still work fine with two-wire balanced connection, but some will not.)
Therefore it makes sense to include the third wire so your cable will work properly with all of them.
The PA-1 has a balanced input... which means that it expects two equal-and-out-of-phase input signals... and subtracts them.
It also has two equal amplifier signal paths inside... which are then "subtracted" by the speaker which is connected across their outputs.
That makes it "a fully balanced fully differential amplifier".
This is just how the ICEpower modules work (we didn't do anything special there).
The XPA-DR amplifiers actually have two entirely separate amplifier modules per channel... each amplifying two equal-and-out-of-phase input signals.
(They are almost exactly equivalent to two channels in a normal XPA amplifier... although the individual gains and rail voltages are different.)
[The original post]
The PA-1 Fully balanced from input section through to output including the amp section according to keith at emotiva. I.e. the entire signal path.
For instance the XPA HC-1 is not fully balanced though it has Xlr inputs. Only its inputs are balanced. But the Emotiva DR-1 is fully balanced on both its inputs and outputs.
All the standard writeups of balanced cables say 3 wires are required. The speaker outputs have 2. There must be a different meaning to "balanced outputs" here. Is it about the circuitry up until the outputs? Or is there a sense in which a 2-wire connection as to speakers can be balanced?
If it is the circuit through to the (seemingly necessarily unbalanced) outputs, is something extra done in regards to the ICEpower module in the PA-1 to achieve that, or is that module, providing its inputs are balanced, inherently balanced in its processing? Does the PA-1 (and the DR-1) essentially maintain two signal paths -- and so work as if two amps -- right through to a recombination of the signals just before the speaker terminals?
