centre pin negative question

[Sean Bartholomew]

what is the purpose of having centre pin negative power transformers
like those commonly used in audio gadgtry eg. guitar FX pedals?

 

[Roger Lascelles]

"Sean Bartholomew" <adrian@rivaband.com> wrote in message
news:b8a337c3.0411251839.2bae7cfc@posting.google.com...

what is the purpose of having centre pin negative power transformers
like those commonly used in audio gadgtry eg. guitar FX pedals?

The center pin of plug packs can be positive or negative. You may have
noticed some sort of pattern, but I wouldn't like to make any rules.

I think the reason for the apparent random assignment of polarity is that
there never was a standard.

If the connector has switchover contacts which switch from battery to
external power, then it may be important which polarity the switch breaks.
I wouldn't think that would matter when using a "wall wart" supply which is
isolated.

Roger

 

[Rich Grise]

On Fri, 26 Nov 2004 11:45:34 -0500, Keith wrote:

"Roger Lascelles" <invalidl@invalid.invalid> wrote in message
news:30nkr1F32tjq3U1@uni-berlin.de...

"Sean Bartholomew" <adrian@rivaband.com> wrote in message
news:b8a337c3.0411251839.2bae7cfc@posting.google.com...
what is the purpose of having centre pin negative power transformers
like those commonly used in audio gadgtry eg. guitar FX pedals?

The center pin of plug packs can be positive or negative. You may have
noticed some sort of pattern, but I wouldn't like to make any rules.

Roger

Maybe not RULES perse, but I've found the bulk of the smallish electronic
gear which uses those "wall-warts" to be center positive. Center positive
is popular enough, that you can "guess" something is CP and be right
probably 95 times out of 100. The most common wall power supplies are 9v
and 12v, although you'll run into the occasional 5/6v models. 3Com, makers
of networking equip, were famous for throwing everything away and using
something goofy like 15 volts *AC* into their mini hubs and switches. Some
small cisco equipment uses 5v and 12v, but uses a molex plastic connector
with 4/5/6 pins instead of the DC barrel connector that most of the other
devices use.

The absolute worst power supply connector I've ever seen was on some
off-brand 8-port ethernet router. The supply was about 3 times the bulk of
a typical wall wart, but had its own AC cord, like a printer supply, but
it was +-15 AND +5, the DC cable was about the bulk of a hand-drill
power cord, but stiff, and the plug was a f***ing MOUSE connector! The
keying on the connector was f***ed up from previous owners trying to shove
it in - it took an extraordinarily delicate touch to feel when the pins
were aligned with the holes, while manhandling that f***ing cable - once I
bent one of the pins, I gave up on it and just tossed the whole thing and
wrote off the twenty or so bucks.

I guess the moral to this story is, if you need multiple supplies, use a
Molex.

Thanks,
Rich

 

[Tam/WB2TT]

"Sean Bartholomew" <adrian@rivaband.com> wrote in message
news:b8a337c3.0411251839.2bae7cfc@posting.google.com...

what is the purpose of having centre pin negative power transformers
like those commonly used in audio gadgtry eg. guitar FX pedals?

Probably goes back to those bitty Japanese AM radios that used PNP
transistors, and grounded the positive side. I don't know what it is, but
there is a sort of standard for the coaxial power connectors. You will find
that for the same OD, there is a choice of center pin diameter. People have
tried to correlate that to polarity.

Tam