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When might an AC (not DC) voltage be used as a power source for an audio device - most every guitar pedal I've ever owned converted line voltage - 120VAC to some lower DC voltage - often 9v or 12v DC. However, my Line 6 guitar processor (POD XT) uses 9VAC to operate - I believe that it is not being converted to DC before powering the circuit - what advantage does designing a circuit to be powered by AC provide? I found one answer here:

http://forum.arduino.cc/index.php?topic=186059.0 "Audio mixers often use AC because they need to resolve positive and negative voltage with respect to the audio reference / ground."

Still not clear - Thanks

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Internally it's taking the AC and converting it to DC. I can't say why, but it's almost certain that it's because they want to have both positive and negative rails, and it's easier to do that if you're getting AC off of the wall-wart.

I suspect that the design (if not the product) is over ten years old, though, because it's gotten so easy to use switching supplies to generate negative voltages, and the switching frequencies are so far beyond audio that the old problem (putting a ca. 20kHz "hum" into your audio) is just not an issue any more.

The only even semi-sensible reason I could see for it not being done is because an older-technology switching supply would be a Very Bad Idea in an audio circuit, and the audio market tends to be quite conservative in what they accept.

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  • \$\begingroup\$ This unit is indeed about 10 - 15 years old and is quite complex - obtaining both positive and negative rails from the source in this way (AC source) makes sense to me. \$\endgroup\$ – Bellflight 14 Nov 5 '18 at 18:53
  • \$\begingroup\$ Another reason might be they expect an AC wall wart not to have any EMC filter (not needed!) so it cannot introduce a ground loop. \$\endgroup\$ – Janka Nov 5 '18 at 18:55

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