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Old 5th Jun 2020, 12:43 am   #508
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
Default Re: MK14 schematic revisions

Your 'tingling' is due to the fact that you are using a un-earthed switched-mode supply. Try this:

-Plug the mains PSU into the mains
-Don't plug the DC power plug into anything
-Set your meter on AC Volts, select manual 200VAC range if possible
-Measure the AC voltage between the outer contact of the DC plug and any known good mains earth, such as one of the metal screw heads on a mains socket.

What voltage do you see? I'm guessing ...~115VAC. That's why you feel a tingle when you touch the 0V areas, such as the modulator casing, on your project.

The 115VAC is coming through a high voltage, low value capacitor which connects the low voltage side of the power supply to the high voltage side in PSUs like this. When you connect the scope 0V to the project, you are earthing that low current AC through the scope's mains earth so that's why the problem disappears when you connect the scope.

Now you see why I never use anything but linear supplies with sensitive old stuff like this.

If you have to use an SMPSU, select one which has a metal earth pin and has the 0V side of the DC output connected to earth. Better still, find or make a linear regulated supply to power these projects.

Last edited by SiriusHardware; 5th Jun 2020 at 12:49 am.
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