DC Jack questions

[Anonymous]

Battling several projects with power supply issues.

1. How can you tell if a DC jack is “center-negative” or “center-positive”?
2. I’ve seen several posts saying “it’s how you wire it.” True?
3. Besides the LED test outside the PCB circuit, is there a better way to test polarity of DC jack inside and/or outside the PCB circuit?
4. Does the material of the input and output jacks matter at the contact points in terms of Ground?

Thanks for the help.

[Cybercow]

Chris . . . . .

1. A DC jack is polarity neutral by itself. How it’s wired determines whether it is negative-center or positive-center. Metal-case DC jacks need not apply – the metal housing always grounds one of the connectors – physically connecting one of the connectors to the enclosure Avoid using metal housed DC jacks.
2. See answer #1
3. See answer #1
4. Yes. Again, see answer #1 – the last sentance.

[Anonymous]

Always using the plastic 2.1mm jacks with the 3 lugs. This really helps a ton. I really appreciate it.

[Anonymous]

Chris,

The de facto standard for “most” stompbox guitar pedals is center negative.  I don’t know why as IMO center positive would be better since Cybercow’s concern about metal jacks would go away.  If you have a schematic of the circuit of interest, there should be a series or shunt connected protection diode that would give an indication of polarity.

[Author]

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