After a little research I’ve discovered that most effects pedals have a negative tip configuration. The first few cigar box amps that I built and sold with a power supply jack were positive tip. I’ve found that a positive tipped power supply is much harder to come across.
If you have purchased an amp before 8-5-2010, please be aware that your power input jack is wired with a positive tip. Connecting a power supply with a negative tip will cause your amp to die immediately as there were no protective measures installed to protect it from a reverse voltage.
This is the wiring diagram for future Cigar Box Amps. It features a negative tip which is compatible with Boss effects pedal power supplies. General Guitar Gadgets sells one for $11. General Guitar Gadgets Effects Pedal Power Supply
The red wire coming from the circuit board is the positive voltage. It connects directly to the barrel contact (Pin 2) on the power jack. The battery’s positive wire connects to the power jack contact (Pin 3). If you run on battery only, the contact (Pin 3) touches the sleeve contact (Pin 2) and current flows. If you plug in a power adapter the battery is disconnected from the circuit to keep the voltage from the power jack from charging non-chargeable batteries. The tip (pin 1) and the battery ground connect to the stereo contact on the stereo input jack. The circuit ground is the black wire coming from the board. It connects to the ring contact on the input jack. When the barrel of the guitar cable is plugged in it completes the ground and turns on your circuit. No switch is needed because your amp turns off when you unplug it.
An optional diode could be installed to further protect against the mistake of wrong polarity. I don’t feel it necessary, but then again it could be like insurance.
This should keep your amp going strong for a long time. If you ever have questions about this, please feel free to post it. Thanks!