When is 9V not 9V?

Measuring Korg 9V power supplyAnswer:  when it’s 13V!

As I mentioned previously, my pedal board’s power supply died, so I’ve been temporarily using an old Korg 9V power supply.

I’ve been getting some hum from Ryan’s Fulltone Fat-Boost, and finally decided to do some sleuthing to figure out why.

Fortunately, before I even cracked open the Fat-Boost, I hooked up a multimeter to measure the voltage output of the Korg supply, and it turns out that this little guy is really putting out 13V, not 9V.    Well, that’s annoying.   Is it mislabeled, or just over-compensating for something?

Measuring 1 Spot 9V power supplySo, I decided to pick up the relatively inexpensive and well-reviewed Visual Sound 1 Spot.    Quoting from the FAQ:   “The voltage output is fully regulated.  It’s at least as quiet as the PedalPower, maybe even quieter.”

Measuring the 1 Spot with the multimeter, I see this one is putting out 9.5V.  I’m guessing 5.7% over is within normal tolerance for a 9V supply.

Better yet, no more hum on that Fat-Boost.

Note to future self, don’t trust power supply labels!


Crazy pedal chain for measuring power supply loadUpdate: Several people asked how the power supplies behaved under load, so…

I set up this crazy chain of pedals, using the long daisy chain that came with the 1 Spot:  tuner, compressor, wah, chorus, hush, two overdrives, two boosts, and a Zoom G3x modeler (!)

I left the final jack in the daisy chain open so I could measure it with the multimeter
Here are the results, under this load:

  • the 1 Spot power supply dropped marginally from 9.52V to 9.40V.  That’s 1.3%
  • the Korg power supply dropped a massive 31.6% from 13.11V to 9.96V
  • for completeness, I also tried the Zoom 9V 500mA power supply (model ADS-5M-12).  This one actually went up slightly from 9.12V to 9.22V (+1.01%)

So I guess the Korg power supply was probably intended to be used with a specific piece of Korg gear, and provided something near 9V when paired with that gear’s load.   Clearly the 1 Spot and Zoom power supplies are better regulated.

Why didn’t I just use the Zoom power supply for the whole chain?  I thought 500mA may not be enough, although it did seem to work ok in this crazy-chain test.  More importantly, it seems to introduce some constant unpleasant buzzing noise in the audio signal when used with the other pedals.  It works fine when paired only with the Zoom G3x.

On the other hand, the 1 Spot, with its 1700mA rating should be enough to power anything I might throw at it—I mean, how much crazier can it get?     Also, interestingly, the 1 Spot did not appear to work well with the Zoom G3x modeler.  While it did indeed power up and work, there was some different unpleasant noise introduced into the audio signal (noise correlated to the activity in the unit, rather than constant noise).

So for now, I’ll continue to use the Zoom G3x with its own power supply, and the 1 Spot for everything else.