Strange electrical sensation only when 'rubbing' amp chassis

[JoeM]

I've had a phase liner that has done this for many years and I've ignored it until now as my new amp that I've just built does the very same thing...
If I lightly rub the aluminum chassis when the amp is on a mild electrical ac 'tingle' can be felt. Doesn't happen when the amp is off. Cant be felt unless my hand is 'moving' across the surface of the aluminum. Both amps chassis are correctly earthed and I cant measure any earth leakage.
I've googled and I think 'body capacitance' is at play here but I dont understand how. Any ideas?

[mikje]

Originally Posted by JoeM

I've had a phase liner that has done this for many years and I've ignored it until now as my new amp that I've just built does the very same thing...
If I lightly rub the aluminum chassis when the amp is on a mild electrical ac 'tingle' can be felt. Doesn't happen when the amp is off. Cant be felt unless my hand is 'moving' across the surface of the aluminum. Both amps chassis are correctly earthed and I cant measure any earth leakage.
I've googled and I think 'body capacitance' is at play here but I dont understand how. Any ideas?

Sometimes the wrong polarity of the AC plug can cause this, specifically for plugs that were made before the wide-spade-polarization-thing (or for DIY projects that might have been reverse wired). Try turning the plug around. I know it sounds strange, but it's worked for me.
Mike

[jaycee]

It could be that the earth in your house is bad. Even with reverse polarity you should not get any tingle on the chassis, as there should be no path to the chassis for the neutral line.

The fact that you cannot measure any earth leakage would make me suspect your building's earth installation. Its worth trying out this test using an earthing stake as the earth point.

[454Casull]

I always get this feeling when I rub the metal chassis of a lamp that is switched on by contact.

[analog_guy]

Use an ohmmeter and measure from the chassis to the ground in the electrical outlet. You should get a reading near zero. Also check to make sure you have the correct polarity on the AC connection. The voltage between neutral-ground should be zero, and the voltage between hot-ground or hot-neutral should be 120V (assuming USA line voltage).

A while back I also borrowed an electrician's plug-in indicator and used it to verify the AC polarity and ground continuity of all the outlets in my house and shop. Some were not correct, so you may want to check in your house also.

[jaycee]

Originally Posted by 454Casull

I always get this feeling when I rub the metal chassis of a lamp that is switched on by contact.

That is because of how the touch sensor works. There is a large resistance between you and the control IC, and it is capacitively coupled, but technically speaking you are coupled directly to the hot line! However, the large resistance ensures that fatal current cannot flow. The resistors are fusible as well so if they fail, they will fail open.

[Bonsai]

You clearly have an earthing or polarity problem.

I would get your house wiring looked into. don't dick around with this: get it looked into by a professional.

[rastanearian]

It's the Genie trying to get out.
You should rub it some more and don't forget to wish for more wishes.