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I'm making a circuit that needs about ±10V for powering audio op-amps. I found a 24 AC/AC adapter, but realized I need a center-tapped transformer for ground. However, I can't find any taking that voltage with 1:1 ratio. It should at least be able to handle 100 mA. The only results at RS, DigiKey and Mouser are made for 110V up.

Am I looking for something that doesn't exist?

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  • \$\begingroup\$ Aside from being somewhat larger than necessary, is there some reason you can't use a 110V 1:1 transformer at 24V? But wouldn't it be easier to just buy a DC-output power supply with the necessary voltages, or in a pinch, use two single-output supplies? \$\endgroup\$
    – Dave Tweed
    Feb 3, 2023 at 0:58
  • \$\begingroup\$ 110V transformers are quite bulky, and I'd like to avoid that. It's a headphone amplifier that will eventually be commercialized, so one of the requirements is a single external wall adapter. It can't have an internal high-voltage supply. \$\endgroup\$ Feb 3, 2023 at 1:05
  • \$\begingroup\$ Something like this ? digikey.be/en/articles/… \$\endgroup\$
    – Antonio51
    Feb 3, 2023 at 6:45
  • \$\begingroup\$ See also: Dual power supply without center tapped transformer. \$\endgroup\$
    – greybeard
    Feb 3, 2023 at 7:37
  • \$\begingroup\$ How are you powering it? \$\endgroup\$
    – winny
    Feb 3, 2023 at 7:50

2 Answers 2

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You might not need a center tap, you can try using two half wave rectifiers to get a positive and negative supply.

Something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

You would need to make sure whatever regulators you use can handle the power dissipation, with a 24 VAC transformer the input to the regulators will be around 34 V, so they're dropping 24 V at whatever current you're drawing. Switching regulators would probably be best, or you could find a lower voltage transformer.

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  • \$\begingroup\$ Switching regulators are extremely tricky when related to audio. On the other hand, 12V AC instead of 24V should be enough (and generally easier to find as an iron core mains transformer). \$\endgroup\$
    – fraxinus
    Feb 3, 2023 at 10:45
  • \$\begingroup\$ A voltage doubler was a good idea. The ability to switch to a lower voltage power adapter is only a plus, so power dissipation in regulator wouldn't be an issue either. I prefer linear regulators for audio. Are there no other downsides to this circuit apport from excess power? \$\endgroup\$ Feb 3, 2023 at 12:46
  • \$\begingroup\$ This is exactly what the "FC Power" Eurorack power source does. Practically the same circuit, with 12VAC in, and three regulators to give the ±12V and 5V of the Eurorack spec. I've built one to use as a bench supply when testing audio circuits. Finding where to buy the 12VAC wall wart was the hardest part. \$\endgroup\$
    – dronir
    Feb 3, 2023 at 14:54
  • \$\begingroup\$ That's quite interesting. To my surprise, AC/AC wall warts were quite easy to source from RS or DigiKey, which is great when designing for audio. It gives a lot of flexibility. \$\endgroup\$ Feb 3, 2023 at 19:18
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You don't need a centre tapped transformer to have a symmetrical power supply.
Options include:

  • obtain a symmetrical power supply suitably specified
  • use a power supply twice the voltage and create a virtual ground:
    Basically, a 1:1 voltage divider feeding a voltage follower, an amplifier with an amplification of +1.
    Have an eye on amplifier stability, especially when adding/connecting bypass capacitors.
  • series connect two same voltage supplies otherwise not connected / "isolated"
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