About power supplies..

[Grumble]

I remember a little discussion about wall plug adapters, and I mentioned that the center pin is not always connected to the positive voltage.
The other day a guy came to my office who had a question/problem about the power supply of a looper.
And look and behold: the power connection is "swapped" from the "normal" way power is connected from a plug adapter...

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[Grumble]

Fireware?

[AlanP]

Centre ground is the global default standard for pedal power supplies. Boss use this, and they have ungodly market saturation.

The reason is that most DC sockets have a switching contact for the ring, but not the tip. So this means that if you are tip-ground, then you can switch the switching ring contact for the positive rail from the 9V battery in or out of the circuit, depending on whether a external power supply is connected. (Using the Ring of the actual guitar in jack switches the battery on and off, not whether it is connected to the circuit or not.)

It's very, very rare to have ring-ground wiring in guitar pedals. You'll usually see it only in -9V pedals, like Dallas Rangemaster clones (and then, the power supply used has to be isolated from the power supply used for +9V pedals in the same signal chain.)

Sorry if I'm being obscure.

[Grumble]

Ok, thank you for your input, it makes completely sense!
Learned something today

[PHOBoS]

I've wondered about this too since it seems to make more sense to use the outside connection for -/GND and the center
pin for +. But for a guitar pedal where the ring of the in jack is used as the power switch (which I always thought of as
a brilliant solution) it does indeed make sense to reverse the power connections, actually it is the only way it can work.

Thanks alan I learned something too

[MusicMan11712]

Excellent point of discussion about the output of power supplies. Interesting insights about the "normal" standard about "wall warts" for guitar pedals; you are a wealth of knowledge, alanp.

Ages ago my first few power supplies for gear were all DC, center negative. I noticed however that phone answering machines tended to be AC. In fact when I needed a replacement for my ART X-15 [midi foot pedal/button thing, aka UltraFoot], the original was 9v AC.

However, the power supply requirement design was rather amazing:

[JovianPyx]

I've seen this several times. It works because while AC is turned into proper polarity DC by going through a rectifier, DC can also pass through the rectifier as well and an additional benefit is that the DC polarity doesn't matter, it gets corrected by the rectifier. There are actually many devices out there that will work with either AC or DC inputs, but they just don't say so.

I've never assigned the attribute "normal" to any PSU connection scheme. It is what it's designer needed it to be either for technical reasons or because "Hey, let's use THAT one because we have two thousand in boxes in the back".

The real fun was in the "old days" when car battery systems were either 6 volt or 12 volt and some had negative ground while others had positive ground. Had to be really careful when jump starting back then.

[AlanP]

"Positive ground" and "negative ground" are a whole 'nother kettle of fish. I've never liked those terms, they confuse people (and me) too much. Ground is a zero volt reference. The power rails can be either positive or negative, though.

It's like diodes and LEDs. The cathode might be connected to ground, or the anode might be. So it's a bit much to talk about the "positive leg" of the diode.

[Grumble]

To make it more confusing: People say that current flows from positive to negative, but since the charge comes from electrons (which are charged negative!) the real current flows from negative to positive

[gdavis]

[JovianPyx]