Power Adapter Issue

Question

I have a Minilogue XD and I'm experiencing micro-vibrations when I move my hand across the metal surface. Functionality-wise, nothing is affected. This occurs when it's plugged in regardless of whether it's turned on.

I've experienced the same effect on Apple MacBooks with the aluminum chasis, and it is clearly a grounding issue. To fix this on the laptop, using a three-prong/grounded AC adapter extension instead of the basic two-prong adapter is all that's needed.

However, with the Minilogue, I'm using the standard 9V DC adapter that does not have a third pin for ground. The Korg KA350 is rated for 100-240V 50/60Hz, and has a US-style two-prong plug. I'm overseas and using an international plug adapter for the outlet (230v). I've tried different outlets and a few plug adapters, but no change.

My immediate concern is figuring out how to eliminate the vibrations on the Minilogue, but I'm also concerned about other gear I purchase having the same problem. Any tips?

Answer 1

This is common to anything using a modern switch-mode power supply.

Technically, they don't need to be earthed, they qualify as 'double-insulated'. Even if the supply itself is earthed the low voltage between that & the device isn't. The 'buzz' you feel is leakage from the switch-mode itself, theoretically harmless, even if slightly disturbing.

The only 'fix' is to manually strap the outer cases to a real earth.
Although a bit of a hokey DIY job, it's safe enough if you do it carefully.
Strap ground wire either to a dedicated ground post, like those hi-fi or rack units sometimes have, or trap in between one of the casing screws [scratch off any paint underneath to make proper contact]. You can link devices together this way, with the last being sent to a regular 3-pin mains plug, connected only at the earth.