|When the Guitar is your voice|
New switch mode power supplies (SMPS) have a major problem.
As a repair tech, I see many blown inputs of mixing desks and guitar pedals. This is due to the increased use of SMPS.
Many power packs have a stray voltage on the output of the power pack, due to no earth pin (two pin AC) and bad circuit design.
The designers use capacitors inside to tie the primary circuit to the secondary circuit. This improves the power supply stabilty.
However, these capacitors charge the secondary side (earth) up to half the mains voltage.
So if you have a USA 110 volt power pack, you can have 40-50 volts on the earth pin of your new power pack.
If you have a Euro 220 volt power pack, you can have 100-110 volts on the earth pin of your new power pack.
To test for this, take a digital multimeter (high input resistance) and select VDC.
Connect the Black lead to the Amp socket (earth) and the Red to the 2.1mm DC plug. Watch the voltage peak and fall away.
The tip of the jack plug is the first thing to touch your earthed Amp socket.
As the Amp is grounded, it shorts the stray voltage, via the tip of your lead and the last pedal in your chain, back down to zero volts.
This can blow sensitive components in your treasured pedal and wreak your musical night.
If you want to continue to use the new style power packs,
then plug all your audio leads in FIRST,
plug the power pack into the AC power LAST.