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9V Adapter

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Pedro Carbonell

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I got a circuit from a magazine that uses a 9V battery.

I want to switch to an adapter. Do I have to just replace the battery in the circuit, or
am I missing something? Maybe a capacitor somewhere.
 
It would help to see your circuit but just replacing the battery with a good quality 9VDC adapter should be fine.

Something like a 100uF 16v electrolytic and a o.1uF polyester capacitor across the supply as it enters your circuit wouldn't do any harm and may help.
 
I got a circuit from a magazine that uses a 9V battery.

I want to switch to an adapter. Do I have to just replace the battery in the circuit, or
am I missing something? Maybe a capacitor somewhere.

You have to know a lot about the adapter you are using; usually more than is stamped on the adapter... I call these things WallWarts, or WW for short.

1. Some WWs contain only a transformer and rectifier(s), either half-wave or full-wave, with no filter capacitor.
2. Some WWs contain only a transformer and rectifier(s), either half-wave or full-wave, with a filter capacitor.
3. Some WWs contain a complete, regulated, DC power supply. This would include modern switch-mode WWs (lightweight), or transformer-based ones (much heavier).

If you happen to grab a type1 WW, you need to follow it with a large electrolytic filter capacitor (hundreds to thousands of uF). If the circuit you are powering requires a tightly controlled 9V (e.g. better than 9V+-0.5V), you may have to add a LM317 type IC regulator between the capacitor and load....

If you happen to grab a type2 WW, you may need to follow it with a large electrolytic filter capacitor (hundreds to thousands of uF) because the one inside the WW could be too small. If the circuit you are powering requires a tightly controlled 9V (e.g. better than 9V+-0.5V), you may have to add a LM317 type IC regulator between the capacitor and load....

If you grab a type3 WW, it might work with no extra components, but if it is an switch-mode type, it may introduce unwanted switching hash (noise) into the downsteam circuit...
 
Most DC wall warts are not regulated. I have some high quality 9V/500mA ones that produce 13V with no load and operate 12V products perfectly when the current is about 100mA.
I have a poor quality 9V/200mA Chinese one that gets hot even without a load and produces 18V with no load.
 
The pedal article does not spec how much 9V current it needs and you do not say how much current your 9V adapter gives. Is your adapter 9VDC or 9VAC? What is its unloaded voltage? How much ripple at the current used by the pedal?
 
If the adapter is a quality one and your pedal circuit overloads it then it simply turns off. But if the adapter is a cheap one from "over there" then it might smoke and burn. You must not overload a cheap adapter.
But you don't know how much current it gives and you don't know how much current it needs.
A quality adapter has its maximum allowed output current printed on its safety certification label. A cheap adapter was never certified to be safe so it might not have a label or it has a fake label.
 
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