Power supply

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Preliminary warning on cheapo wallwarts

Unregulated DC wallwarts (the most common kind) are rarely labelled in a meaningful way. When a manufacturer sticks a "12V" label on a product it could mean:

  • The voltage output by the wallwart when sourcing X mA will never fall under 12V. Under a lesser current load, the actual voltage is higher.
  • The wall-wart will always deliver at least 12V, though some units in the batch might deliver 13V or 14V.
  • 12V is the mean value, there's a 10% or 20% standard deviation around that.

As a result, be extremely cautious when using a power supply approaching the maximum ratings!

Regulated or switching mode PSUs are more trustworthy!

Shruthi-1, Anushri

  • 7.5V to 12V. The higher the voltage, the higher the heat on the 7805 and 7905 regulators. An input voltage above 15V, even for a short amount of time, is going to damage the LT1054 - as a result, there is a risk of damaging the Shruthi-1 even with a 12V supply (see the warning above).
  • >200mA. Note that this is often wrongly reported on the power supply specs, so 300mA is a minimum.
  • Switching mode PSUs have been known to work.
  • Center tip positive.




  • 9V AC. 12V AC will cause excessive heating on the 7805 and is not recommended.
  • >600mA.
  • Polarity does not matter.



  • 5V to 9V. The higher the voltage, the higher the heat on the LM1117 regulator. Note that this is a LDO regulator, it should work with as low as 4V indeed!
  • The MIDIpal draws less than 100mA, so current ratings should not be an issue.
  • Center tip positive




  • If you have a spare mobile phone charger (who doesn't?), it's probably worth checking the voltage it provides. Lots of them deliver 5v under a few hundreds mA. Generally, you can easily swap the plug with a standard Jack DC 2.1mm (beware the polarity!). A convenient and environment-friendly way of getting a PSU for little to no money!