If a marketing person tells you their circuit is balanced, then you have a reasonable expectation you will enjoy the full benefits of balanced audio. In many cases you might be wrong. Not wrong in your expectation, wrong in what you get.
Let’s take a look at what a typical balanced input might look like. I’ll use the same drawing we had yesterday.
V1 and V2 are the two inputs, Vout is the output. Simple. And this circuit will give you the expected benefits of a balanced input. But it is not a balanced amplifier topology and this is where we wind up getting confused or, in some cases, misled. The circuit above is a balanced input amplifier with a single ended output. It is what many, many amplification circuits do: add balanced capabilities to a single ended topology. We cannot say this is a balanced audio approach. No, we can only say it has a balanced input. Now let’s compare to a true balanced design.
Yes they are very different. The true balanced circuit is discrete where the first example shows a simple op amp. But the designer can use either op amps or discrete to make a true balanced design. Note how the true balanced design has two inputs as well as two outputs and everything remains in two’s? We’ll look more at this topology tomorrow.