I have an audio source input, that I am putting through the circuit below to create a balanced audio signal.
There will be one of these for each channel, left and right.
I have been asked to provide a "balanced or unbalanced switch", so that a user can flip the switch and have either balanced or unbalanced audio out.
But, as far as I can tell, if you want unbalanced audio from this set up, you would just take the audio from pins 1 and 2, and dont connect pin 3. This gives you an unbalanced audio output.
If I added an extra stage to combine the balanced audio to unbalanced, then I would just be converting back to the original input signal.
Or am I missing something here?
Is there some way to add an "balanced or unbalanced switch"?
Best Answer
Firstly, that's a differential output, not balanced.
A true balanced output would couple interference on one leg to the other, improving common mode rejection at the receiver.
To test : short either leg to ground. If the amplitude on the other leg doubles, it's balanced. This has two consequences :
However, differential may be good enough for your purpose, and it's not unusual outside pro audio.
As you say, hot + ground comprises an unbalanced signal.
But if you want to make an unbalanced output on pins 2 and 3, you could simply disconnect teh cross-coupling resistor from the -ve leg, leaving that amplifier as a voltage follower with 0V input.
The trivial way to generate a balanced output is to use a transformer; the secondary provides a fully floating balanced output.
For an example of a transformerless balanced output driver, see the SSM2142 which can be replicated with opamps and matched resistors if you like.
Some further discussion in this Q&A: attracted quite a few answers, of which mine was only one.
And also this one