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I have Korg's Wavestate synth. https://www.korg.com/us/products/synthesizers/wavestate/

It uses 12VDC PSU with two prongs, hence it has no ground pin. My power outlet is 220VAC. When I connect the synth to the power without turning it on, and no other cable connected to it, I can feel electrical sensation from the front metal panel. Of course, this goes away when the chasis is grounded to the wall outlet ground pin.

I measured the VAC between the metal plate and my hand with a digital multimeter and it was over 80VAC. The amperage between the metal plate and a ground pin from the wall outlet was measured at around 0.2mA AC. It wasn't high but I can definitely feel the electricity while operating the synth.

What I really wonder is how that 80 VAC comes out if it's powered from 12VDC adapter? I couldn't find any clue from my search.

June Kim
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    Will this answer your question? https://electronics.stackexchange.com/questions/216959/what-does-the-y-capacitor-in-a-smps-do – Justme Sep 24 '20 at 19:26
  • sounds damaged... and if you not have a earth leakage circuit breaker... I personaly would stop touching metal parts – schnedan Sep 24 '20 at 19:45
  • The intention is that it's connected to a grounded system, and doesn't want to add another ground connection to make a ground loop. Its adapter is pretty heavy, right? It uses a 50Hz AC transformer which has parasitic capacitance to the primary ... one end of which is 0V, the other end is 220V. So you can expect about 110V AC at a very high impedance to ground ... quite harmless. –  Sep 24 '20 at 20:26
  • It's to do with how the power adapter is wired to avoid it creating too much electrical interference. You could try to get a class 1 adapter with an earth pin, which won't give that tingling. – Andrew Morton Sep 24 '20 at 20:32
  • @BrianDrummond I don't recall reading anyone complaining about non-switch mode PSUs giving electric shocks. I know my linear bench PSU doesn't, and that's got isolated outputs. – Andrew Morton Sep 24 '20 at 20:35
  • Your linear bench PSU with isolated outputs probably has a mains transformer with "inter-winding screen" (sheet of copper with ends insulated so as not to form a shorted turn, and grounded). That effectively eliminates capacitive coupling from pri. I have measured it as 110V open, 30uA short cct, on an audio preamp (toroidal) transformer. –  Sep 24 '20 at 20:40
  • Normal Y-capacitor leakage. Nothing to worry about. – winny Sep 24 '20 at 21:05
  • @schnedan no it is not damaged. It is the EMI Y cap from low voltage side to mains side in a switch mode power supply. – Justme Sep 24 '20 at 21:30

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As you noticed there's generally a capacitive connection between the DC output and the high voltage side of the power supply. The given comment directs you to an explanation which tells it reduces radio interference. It unfortunately in ungrounded systems bring mains AC voltage onto your hands through capacitors.

The capacitive impedance is high enough to prevent painful shocks, but you can easily feel it. If you wipe with your fingers on a very thinly insulated, say anodized aluminium surface the electric field can be so strong (volts per meter) that it changes the friction (via changing the force) of the wiping and you feel 100Hz roughness which do not depend on how fast you move your finger.

If you have one device in your system properly grounded the effect vanishes because also the synth is grounded and that shorts the leaked AC. But that is also a danger. The grounding happens via signal cables. If you connect or disconnect an audio cable so that the signal terminal connects first or last the audio circuit can enjoy the leaked mains AC and get destroyed. The hot tip of a 1/4 inch audio plugs virtually every time touches metal (=gnd) first when plugging in and last when disconnecting.

The danger grows by a magnitude if you have devices which have grounded mains AC plugs but someone has inserted tape or otherwise broke the grounding to reduce ground loops which catch unwanted noise to the audio system. They say "it's grounded via signal cables, it's safe". Maybe it's grounded but only as long as the signal cables are connected. I cannot accept that thinking, because power supplies which are designed to have grounded AC supply leak easily 1000% more than your power supply. If the grounding doesn't happen very painful shocks are probable. In addition removed grounding make the system illegal, it's an intentional safety code violation. The ground remover is treated as a criminal in case something happens, say a fault which causes damages.

What to do: have one device in the system as grounded but be sure nobody connects or disconnects inter-device cables before the mains AC cables of the system are 100% unplugged from the mains AC outlets. I have seen how music bands have only a single mains AC plug to keep things under control.