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Craig, Ted has a question...

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Why thanks, Dr. Destructo...


I know...I should have asked Craig in the first place, but he should ask (and rightly so) "So, Tedster, you DON'T have a copy of the book...hmmm???"


(Rather embarrassed look on face)...


(Peter Sellers Indian accent)..."I swam the deepest deserts, climbed the steamiest valleys...crossed the burning tundra...to ask you, O Great Sage...the secret to power supplies for stompboxes".


Like I said in the other post...I really haven't used much in the way of stompboxes until recently...

"Cisco Kid, was a friend of mine"
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Yeah, I have thumbed through his book but never bought it...YET.....and I want to build a Theremin something awful, or one of those filter sweep units.
Down like a dollar comin up against a yen, doin pretty good for the shape I'm in
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Well, not much to add to the comments in the guitar thread, except that universal power supplies are a good bet. As long as the voltage, polarity, and current ratings are satisfactory, you should be okay.


The question of noise from an AC supply varies. There are two parts to a power supply: the rectifier, which converts AC to pulsating DC, and the filter, which smooths out the pulsating DC. Most generic AC adapters do not include filtering, which is okay because many devices have filtering built in. Those that don't require custom AC adapters that include filtering.


The next step up is an AC adapter with regulation. That's the kind I wrote about in my book. With regulation, the voltage coming out is constant. My supplies are also short-circuit protected.


The issue of current rating is more complex than it first appears. One would think that if a device is rated at 300 mA, then a 600 mA supply should work fine because there's a huge margin of safety. But there's a catch: cheapo supplies generate more voltage than you need, and depend on current drain to bring it back down. In other words, an adapter may deliver 12V with no load, but drop down to 9V under their rated load. If the load is substantially less than the rated load, the voltage may only drop to 10 or 11 volts. That's why it's safest to get an adapter that's rated at the same current as the one it replaces.


With all the effects I designed, you can plug the adapter in backwards and nothing bad will happen because there's a "safety diode" that shunts current to ground if the adapter is plugged in incorrectly. Most commercially-available effects that I've seen do not offer this protection, so be VERY careful about the polarity.


One final thought: do not leave AC adapters plugged into the wall when the unit being powered is off. There is nothing to draw current from the transformer, and Eddy currents can occur that heat up the transformer. I highly recommend plugging your wall warts into a barrier strip, leaving the devices they power on, and turning off power at the barrier strip, not the effects.


Hope this helps...

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