Potentially lethal situation?

[Van_Sloth]

Hi!
First of, I'm new to this forum, so pardon me if this isn't the right place to post at.

Now here's the problem:
I'm a musician with a home studio. I currently have my laptop charger in one socket and my tube amplifier in another one. If I turn on the amplifier while the computer is still plugged in, the laptop starts vibrating slightly(or atleast that's the sensation I get while touching it), and if I touch the side of the laptop screen, I get a slight shock!

I have no idea why this happens, and I'm afraid it might be very dangerous.
Any ideas what might be causing this?

Thanks.

 

[Marvo]

Is your laptop plastic or metal construction?

 

[Lucien Nunes]

The vibrating sensation is probably not actual vibration, but the sensation of a small amount of AC leakage current passing through your hand. It is most noticeable if you stroke a metal surface lightly, such as the body of an Apple laptop. In this way, your body can detect very tiny, harmless currents. Laptop chargers themselves produce leakage current which can sometimes be felt in this way, but it is impossible to distinguish between this and a dangerously live appliance casing, without proper testing.

1. Are these two devices connected to a grounded (3-pin or Schuko) outlet?
2. As per Marvo, is it a metal bodied laptop with a 3-pin power cable on the charger?
3. Is it a vintage amplifier?
4. Do you know what type of grounding your studio's electrical supply uses?

If the buzzing sensation and shocks only occurs when the amplifier is switched on, there is possibly a fault in the grounding (earthing) of your electrical outlet or circuit, and/or a fault with the insulation or wiring of the amplifier. At this stage we can't tell which. If the laptop charger has a grounded mains cord, leakage current from the amplifier can pass through the ground connections to the laptop, instead of to ground, hence one appliance causing a shock sensation at the other.

Musical instrument amplifiers are notorious for having modified and dangerous internal wiring, where people have altered them time and again over the years.

Subject to the answers to your questions, you may need to have the electrical safety of the amplifier professionally tested, and/or the wiring in the Studio. If you are using an extension cord to supply both items, that is a prime contender for a faulty ground connection.

 

[Marvo]

It's worth reminding that to get a shock or a tingle from the chassis of an appliance you're probably going to need to find two separate faults. Firstly there's probably a low insulation (IR) problem on one of the devices and secondly a lack of earth that's allowing a voltage to develop on the chassis.

Sound studios can have unorthodox earthing arrangements in order to eliminate electrical noise and secondhand equipment from sound studios may have dual or multiple earthing points. I'd suggest an experienced commercial electrician might be the way to go, if you let a novice loose with a mega tester on recording equipment there might be damage caused.