Hello! I have this one older AC-DC adapter from Korg (wallwart?)...

Korg AC-DC 9V Adapter

...that I have been using for my (guitar) effect pedals for a few years, and I recently found out (when I was doing some electronics doodling) that the adapter gives much more voltage than it's supposed to. I should give out +9V (as it is clearly seen from the picture), but when I measured the voltage by my multimeter, it is showing...

AC-DC Adapted voltage measurement

...more than 14V! It freaked me out a little bit, since I may have been using it like this as a +9V adapted for my (expensive) delay, and that certainly could have been good for the pedal.

Does anyone have an idea of what's wrong with the adapter, since I have never opened it up or messed with it? Or am I measuring it wrong? And possibly, is there an easy fix?

Thank you!

EDIT: How can I find out that the adapter is "unregulated" (is it the same as unstabilized?) and it's not broken?

  • \$\begingroup\$ My 12V dc Yamaha wall wart outputs about 19V DC when unloaded. \$\endgroup\$ – Andy aka Mar 3 '16 at 11:48
  1. Obviously, you have an unregulated power supply. If it's rated for 9V@600mA, and producing 14V2@Open.

  2. To test for its output while driving your pedal, take the cover off your pedal (usually a trivial matter of removing a few screws); plug in the wall wart, then connect your meter leads to the pins of the peda's power jack. This will show you the highest voltage it's pushing into your pedal & let you get a better idea of how much to worry.

    • Remember, for most electronic equipment, overcurrent is more damaging than overvoltage. The only time that overvoltage without overcurrent is likely to damage equipment is when it exceeds the breakdown voltage of a component; most manufacturers will likely eaither include their own Vreg in an expensive piecd of equipment, or spec all their components to have a much higher breakdown voltage than the 'nominal' input voltage.

Two options:

  1. Well.. it might have gone bad but I doubt that.
  2. More reasonable explanation is it gives off a bigger voltage than it is supposed to because it is unloaded. By that I mean that there is nothing connected to the power supply:

Let's take cars as an example. If you would measure a cars battery when the car is not running and when it is running (more so when you are starting it) I guarantee you that it would show a lower voltage when you are running it.

It is called voltage drop. (or vdrop) Will there be any voltage drop when connecting load to batteries?

enter image description here

Regulated supplies, without any load, should measure very close to the target voltage of 9v. Unregulated supplies will generally have a no-load voltage anywhere from a couple of volts to several volts higher. So your supply is unregulated and that is the reason why it shows a way bigger voltage than 9v.

To simplify, I would not worry about it too much - the power supply is probably running well and working well.


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