Balanced Audio Line Driver Off Single Supply

Question

I am working on a device that needs a balanced audio line driver that can convert an unbalanced signal to balanced and drive a balanced cable run between devices. I am looking at schematics using devices like the THAT1646 and also op-amp circuits that can do this, but the all seem to run off a bipolar supply (+/-15V, +/-12V, +/-9V, +/-5V, etc), whereas my device needs to run off a single ended supply (+9V only).

Does anyone have a circuit they can share to do this on a single ended supply?

Update: Would prefer to avoid using audio transformers. Looking for an IC or op-amp based solution.

Update: Looking for output to be hot, cold, ground (3 wire). This is meant for balanced xlr audio connections.

Answer 1

If you are OK with using transformers, a simple audio transformer with a center tapped secondary will convert from unbalanced / single-ended input to 3-wire balanced output, and does not require a bipolar power supply.

^{simulate this circuit – Schematic created using CircuitLab}

In this circuit, the transformer needs to be able to tolerate whatever DC component may be present in your unbalanced input.

Also, it is assumed in this circuit that whatever is driving the single-ended unbalanced input and the transformer primary have suitably matched impedances. Similarly for the secondary impedance. That is, not just any transformer will do.

You can eliminate the DC component entering the transformer by adding a capacitor.

^{simulate this circuit}

However, you still need to ensure that the transformer's impedance is suitable for the driver.

Answer 2

Now that you have clarified that you do not want to use transformers, here is a circuit that may possibly suit your needs.

^{simulate this circuit – Schematic created using CircuitLab}

The op-amps can be single supply. They are biased to 1/2 of Vcc.

This circuit will run in the CircuitLab simulator.

Since you may be using 8 of these circuits per device, there is a small optimization you can make. You could use 10k\$\Omega\$ resistors for R3 and R4 and share the divided voltage across all the circuits. Not a huge savings, but some.