A little more about balanced and differential amplifiers.... Jul 26, 2019 9:42:37 GMT -5 repeetavx, mick, and 1 more like this
Post by KeithL on Jul 26, 2019 9:42:37 GMT -5
Here's a short description about the difference between "balanced" and "differential"...
The term "balanced" in general refers to a situation where two cables, or two amplifier channels, carry copies of the audio signal that are equal but out of phase.- the term "balanced" generally refers to amplifiers or signal paths ("a fully balanced amplifier"; "a balanced input or output"; "a balanced signal path"; "a balanced cable")
The term "differential" refers to a situation where you have two inputs or connections, and differences between them are amplified or passed, while signals that are common to the two are ignored.
- the term "differential" generally refers to a type of circuit
So, for example, a balanced cable carries two identical, but out of phase, versions of the same audio signal.
When you then connect this balanced cable to a balanced input it is usually passed to a differential circuit.
This differential circuit keeps the desired signal - by passing and amplifying the difference between the signal on the two input lines ( when you subtract the inverted signal from the non-inverted signal you get 2x the signal).
And the differential circuit discards most noise picked up by the wires ( any noise picked up in transit is likely to be the same on both wires - so, when you subtract one from the other, most of the noise is cancelled out).
HOWEVER, a differential circuit is also used internally in almost all modern amplifiers, even on the unbalanced inputs, to compare a portion of the output signal to the input signal (as part of how NFB works).
So, when you have a balanced input, but each of the input lines is already connected to its own differential input circuit, the whole thing can fairly be described as "dual differential".
And, if you have a balanced amplifier, and each of the two amplifier channels has a balanced input, and each of those input lines is connected to its own differential input circuit, you can fairly call it "quad differential".
It's also important that what we're talking about is "function blocks" - which is a fancy way of saying "what stuff does".
For example, most modern amplifiers have "an active differential input circuit", which is quite easily recognized on a schematic.
However, the balanced transformer inputs on vintage microphone preamps, and are still used in some equipment today, are a very effective form of PASSIVE differential input circuit.
(They are no longer commonly used because they have several important disadvantages.)
An engineer will simply look at the schematic and notice where various balanced connections and differential circuits are used.
HOWEVER, while the term "balanced connection" is pretty much standard, the terms you use to attempt to describe the other stuff to a non-engineer aren't....
Therefore, we do our best to use terms that are both descriptive of what's actually going on, and that sound cool in the marketing literature.
The takeaway is that, if you find all this terribly confusing, then you shouldn't really worry about it quite so much.....
All that really matters is the results it produces in a given situation and how it all sounds... right?