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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.

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  • \$\begingroup\$ The SSM2142 does this although it's becoming obsolete, but I expect you can still find some. Or is it for a new product? \$\endgroup\$ – Finbarr May 10 at 14:04
  • \$\begingroup\$ Do you care whether you have a two wire balanced line, or a three wire? (2 signal and 1 ground?) Are OK with using transformers? \$\endgroup\$ – Math Keeps Me Busy May 10 at 14:17
  • \$\begingroup\$ @MathKeepsMeBusy just added updates. 3 wire, no transformers. \$\endgroup\$ – Emmett Palaima May 10 at 14:57
  • \$\begingroup\$ How many of these devices are you making? How much design/test/debug effort should go into project compared to simpler but more expensive per device solutions? \$\endgroup\$ – Math Keeps Me Busy May 10 at 15:04
  • \$\begingroup\$ @MathKeepsMeBusy probably a fairly small run at first (5-10 units), but each device needs 8 independent balanced outputs, so some reduction of cost is prefereable \$\endgroup\$ – Emmett Palaima May 10 at 15:07
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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.

schematic

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.

schematic

simulate this circuit

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

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

schematic

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.

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