My mini-amp project has been on hold for, among other things, the lack of a suitable power supply. But my Norelco electric shaver recently crapped out, and I replaced it- leaving me with a 12VDC 3W wall wart used to charge the shaver's batteries.
This ought to work fine for the mini-amp, and I cut off the plug to find real copper wire, suitable for soldering to the amp connections.
I looked closely at the plug before removing it. There was no polarity marking on it whatsoever; it had a "U" shape to the plug to ensure a one-way-only connection.
So now I have 2 bare wires. This is probably a stupid question, I'm sure there's a obvious solution, but I can't fathom it at the moment. How do I ascertain which is the + and which the - ? If this can be done with a multimeter, I'm not sure how.
Hi newey - a 3w charger might not have enough grunt to power an amp, and it might not be smoothed. But, in answer to the question, the 20V dc voltage setting on your meter should do it. It will give a + voltage reading if the black com wire goes to negative and red wire goes to +. You can check that with a battery.