Discussion in 'Electronic Basics' started by ElectricWind, Dec 8, 2003.

1. ### ElectricWindGuest

I have a Roland XP10 keyboard that requires a 9v 1000 mA ac to dc adapter.
I lost the original one, and I don't want to purchase one form the company
becuase it is overpriced, but I could not find a matching one from Radio
Shack. I asked a teacher of mine what I could do and he said i could use
one I found that was 9v 1300 mA because the keyboard would not use the extra
amps. Is this correct?

2. ### Ian StirlingGuest

Yes.
Assuming that the XP10 does not require a regulated power supply.

3. ### defaultGuest

Yes

Make sure the polarity of the connector is the same as the original .
.. . reversing polarity can get expensive

4. ### John PopelishGuest

Yes. At less than a 1300 ma. load the the voltage will be a bit
higher than 9 volts, but probably not enough to cause any problem.
You can measure the no load voltage and approximate the voltage
between that zero current load and a 1300 ma. load with a straight
line. E.g. If the open circuit voltage measures 11 volts, then at
1000 ma. the voltage will be approximately

(11-9)*((1300-1000)/1300)+9=9.462

5. ### ElectricWindGuest

Wouldn't pluging the adapter in the reverse way reverse the polarity? The
prongs on my orignal were both the same size, so does that mean its
protected or somthing?

6. ### JeBGuest

the plug from the ac adapter to the keyboard needs to have proper
polarity ... both polarities are commonly available. If your keyboard
isn't polarity protected, the wrong polarity "can get expensive".

7. ### defaultGuest

That's interesting. There are only way two ways I know of
"protecting" the electronics from reverse polarity, one is with a full
wave bridge rectifier - then the diodes steer the current in the
proper direction. The reason I doubt they do that is because it makes
the DC transformer redundant - AC would work if that's the case; so I
doubt they would use a DC transformer unless they wanted the option to
use either - unlikely when manufacturers build to save pennies.

The other way is with a diode that shorts the supply if it is
connected incorrectly. That usually entails a fuse to protect the
power supply from damage and keep the diode from smoking.

Your keyboard is chock full of circuitry that is bound to be sensitive
to polarity.

If you mean plugging in the AC in the reverse way - at that end it
doesn't matter.

Where is the plug - socket you are referring to?

The prongs can be the same size and they can use a physical barrier
that forces you to only plug it in one way.

Look at it more closely, are you absolutely positive that you can plug
the DC end in with either polarity? Absolute certainty - stake your
life on it certainty (well your keyboard's life anyhow).

That seems somewhere between highly unlikely (but still possible) and
totally unbelievable.

Measure twice; cut once.