12-06-2020, 05:26 PM
With some mains switches you can get an open circuit reading with a DMM. This is due to tarnish on the contacts. Mains will blast straight through it but the very low voltage applied by a DMM may not. I've had this problem with old TVs which haven't been run for many years. If you have an analogue multimeter that will usually apply enough voltage to check tarnished contacts. If your DMM has a diode test range, that normally applies about 3V which may be enough. Battery and bulb is another way.
When checking a DP mains switch make sure you're not trying to measure between the 2 poles. This will always read open circuit. If you wire it that way it will blow the mains fuse every time you turn it on. Been there, done that, but only once.
The volume pot will work without the switch. Using a separate switch you may be switching off with the volume at other than zero. This may give a worse pop. Easily checked by bypassing the existing switch and switching off at the wall socket.
There is no real advantage in using a DP switch. It's nice to isolate the kit when switching off but remember that the switches in mains sockets are usually single pole.
When checking a DP mains switch make sure you're not trying to measure between the 2 poles. This will always read open circuit. If you wire it that way it will blow the mains fuse every time you turn it on. Been there, done that, but only once.
The volume pot will work without the switch. Using a separate switch you may be switching off with the volume at other than zero. This may give a worse pop. Easily checked by bypassing the existing switch and switching off at the wall socket.
There is no real advantage in using a DP switch. It's nice to isolate the kit when switching off but remember that the switches in mains sockets are usually single pole.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
