What is the purpose of phase inverter?

[RemoGaggi]

I am thinking of attempting to build a DIY DAC and some kits say they are phase inverting. (Scott Nixons DACkit). Whats the reasoning for this? Why would I want to invert the phase???

Thanks.

[Steve Eddy]

Originally posted by RemoGaggi
I am thinking of attempting to build a DIY DAC and some kits say they are phase inverting. (Scott Nixons DACkit). Whats the reasoning for this? Why would I want to invert the phase???

Hey, someone else from the Sack O' Tomatoes.

Anyway, "phase" probably isn't the best term to use. "Polarity" would be better. And it's not necessarily what someone wants, but rather a consequence of the type of circuit used.

Most DACs which have current outputs and require current to voltage conversion have the polarity of their outputs inverted. That's because they were designed expecting to feed an active current to voltage converter which typically takes the form of an inverting opamp.

In that scenario, the DAC's inverted output combined with the inverting opamp stage results in the "proper" polarity at the output.

But if you use passive current to voltage conversion, which is often just a resistor, there's no subsequent signal inversion after the DAC as in the case of the active solution, so the polarity of the output remains inverted.

se

[Archwn]

Output of the TDA1541 is phase inverted. So you invert it again to get the right phase.

The datasheet also shows its output stage opamps in inverting configuration. Though I can't find any information on the TDA1542

TDA1543 datasheet, on the other hand, shows NE5532 opamp output stage, still inverted.

[preiter]

Some people say they can hear polarity inversion. It's not a big deal either way.