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Re: "Overpowering/frying" my effect pedal

7/13/2000 1:42 PM
Mark Hammer
Re: "Overpowering/frying" my effect pedal
It's also a good idea to have a regulator in line of *known* value. Many of the switchable voltage adaptors provide very little regulation beyond a couple of diodes and a modest value cap. Having a little in-line adaptor box with a 9V regulator, bigger cap (e.g., 1000uf/25V) and power LED is a nice thing to be able to plug in between whatever adaptor happens to be handy and your cherished effects.
7/13/2000 3:03 PM
why multiadapters are innaccurate
The adapters ar eNOT as inaccurate as you all think they are. Say you have a multiadapter set at 12 v, and you measure 18v on it, that is because the power supply is unloaded. IF the adapter is for exapmple, 1A @ 12v, and you have no load on it when you measure it (a voltmeater's load is negligible!), of course it will soar! SO by ohms law, V=IR, you get V/I = R SO to get 12V at 1 A, you have 12/1 = 12ohms. NOW try putting a 12ohm resistor (make sure we are talking a 15w power resistor or so!), NOW measure the voltage... voila, you are now drawing 12V! The point i'm making is, the selected voltage determined at the curent rating of the transformer. SO in the case of powering a couple stomp boxes, bigger is not always better! IF your pedals draw a few hundred milliamps current, and the transformer is rated at a couple amps, you better either set the power supply for a lower voltage, or throw in a big resistor or a zener or two to load it more. The ideal solution would hbe to get a transformer closer matched to what you need
7/13/2000 10:50 PM
Frank Clarke

True. Some people think that unregulated 9VDC 200mA means that it always puts out 9V up to a maximum of 200mA. So they think that a higher mA rating is better. But this is not the case.  
To be safer, you might spend a couple of bucks on a voltage regulator. You could take RG's schematic:  
and add everything to the right of the "Full wave Br." to your 12V wall wart, in a separate box.  
This will prevent too high a voltage getting to your pedal.
7/13/2000 12:56 PM
Re: "Overpowering/frying" my effect pedal
Check and see if a 9 to 11 volt zener is used as a protection device, if so replacing the zener MIGHT fix it.
7/14/2000 3:56 AM
Most of the variable voltage adapters I have seen have come with universal plugs that allow you to switch polarity. I imagine being a Korg they put a diode in for protection but you never know. Maybe coulda sent upwards of +twelve volts to ground and fried it that way. Follow the leads from the adapter jack and hope the meet up with a diode.

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