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I'm designing a power section for my guitar pedal circuit that will supply power to my pedal using either a 9V power supply or a 9V battery. I'm using a switched barrel jack but I'm not sure if I have it wired up correctly, I do know that the center pin should be negative. Before I build it to test I was hoping that I might get confirmation if I've got things arranged correctly? Thanks!

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Center pin should be positive in my experience - experience which includes developing products using that kind of DC power jack. Check Digi-key, Mouser, etc - typical wall-wart suppliers like CUI or Phihong are center-positive by default for barrel connectors.

Use a pair of diodes to isolate the battery from the plug. The BAT54 type has lower Vf (0.3V) than 1N4001 (0.6V) so loss is less. BAT54 is 1A, but it could be used in place of the BAT46 you have elsewhere in the design. They make 4 different kinds of BAT54: single, common anode, common cathode, and series (BAT54, 54A, 54C and 54S, respectively) so it can reduce component count.

Another choice is center pin size. I used 2.5mm for 5V and 2.1mm for 12V, to prevent plugging a higher voltage to a lower one. 2.1mm would be better for your case.

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  • \$\begingroup\$ I checked my power supply and I get +9V when the negative probe touched the inside of the plug (pin) and the positive probe touch the outside of the barrel. I also got additional info from this site about wiring up power. neatcircuits.com/doctor_pedal.htm \$\endgroup\$ – greyBow Jul 23 '19 at 0:44
  • \$\begingroup\$ This might be a custom supply. If it ever blows up, and you want to replace it, you will have to get it custom again. \$\endgroup\$ – hacktastical Jul 23 '19 at 0:50
  • \$\begingroup\$ One way to avoid any possible issue is to treat the supply as if it were AC: use a full-wave bridge. Then you won’t care. \$\endgroup\$ – hacktastical Jul 23 '19 at 0:56

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