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I have an audio interface called an m-audio profire 2626 (made sometime in the late 2000's) that's just a solid metal box that takes inputs form mics and 1/4 jacks - it only has a two prong plug-in which is currently plugged into a surge protector that has three prongs. Firstly, is this device safe without the three prong? Furthermore, I have other things plugged into the surge protector that are grounded. If I were to turn on one of the guitar amps (three prong) while I have earphones on my head connected to the audio interface (two prong) would this cause a difference in potential and possibly be a shock hazard?

The reason I ask is because last night I was recording something with the interface and I had my foot propped on the amp (classical style guitar) and I accidentally switched it on the bass amp (three prong) with my foot - the pop startled me and I did notice that the headphones sounded like static for a moment - to be honest not sure if I was just listening to the pop from the amp or if there was a little tiny shock. The fact that I could barely tell - I assume getting a bad shock would be much more obvious and painful. I don't want to find out.

Would it create a circuit if I touch something that's plugged into the same surge protector?

Should this interface have the three prong outlet like most other metal bodied appliances? It takes 12v.

I'm about 99% certain that the ground is done properly. This place was built somewhat recently, but I could get an outlet tester and double check.

  • Does the device's power supply have a "square-within-a-square" symbol on it? – ThreePhaseEel Jun 12 '15 at 22:14
  • Yes it does have a square within a square on the power supply – Kolob Canyon Jun 14 '15 at 19:46
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I don't know this device specifically, but it is possible for it to be designed to be "ungrounded". There are several reasons for this. One is that if it's using an external power supply.

Audio circuits can be designed with an audio ground and a power ground. If they are connected together and then grounded through the wall socket, you usually get a hum-loop. One way to avoid this is to build the audio device without an explicit power ground.

But whatever the reasons, if you are using the device as it is intended, including using the power supply it came with, there should be no problems.

  • I checked and there is a box within a box on the adapter which I believe means it's double insulated? – Kolob Canyon Jun 14 '15 at 19:45
  • Yes, it does. It's double-insulated and does not require a ground to the power socket. – staticsan Jun 17 '15 at 4:28
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Since your audio interface is powered by a double insulated supply, yes, it is safe to use -- double insulated supplies rely on a thick insulation barrier to protect against shock.

The 'pop' you heard was caused by a DC bias being present on the output of the amplifier on startup, and does not represent a safety hazard, except perhaps to your speakers.

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