12V adapter + resistor = 9V adapter?

[Pharaday]

This one seems kinda silly, but a buddy of mine suggested it and it seemed so crazy it might just blow my electronics... I mean work. I want to add some resistors to a 12V adapter to make a 9V adapter. I know that the amps is what I need to look at. I've seen one working, tested volts etc. but I figure he musta got lucky with the amps. What must I take into account to do this? I'm trying to power a flange pedal that wants 9V but it doesn't say how many amps it wants. It can also be powered by a 9V battery, if that halps. If it doesn't halp, well there it is anyways!

 

[davenn]

Although you can drop the voltage using a resistor, it also drops the available current considerably
and the resistor will get really hot. There will be absolutely no voltage regulation and the output voltage
will depend on the load resistance.
a resistor and a 9V Zener diode would be a bit better but still no stable regulation
a 7809 regulator is the best way if your expected current drain will be 1A or less


Dave

 

[Alec_t]

I can't believe a flange pedal designed to run from a 9V battery (presumably a PP3 size) would draw more than a few mA. Therefore a zener-based regulator would probably suffice. A 7809 looks like overkill. Do you have a schematic for the pedal?

 

[BobK]

Use a 7809. Here is a link to the circuit.

http://www.harrington.jp/diy/simple-9v-voltage-regulator-circuit/

You probably do not need the capacitor on the input, but on the one on the output is important.

Bob

 

[Alec_t]

Be aware that the LM7809 has a quiescent current as high as 8mA (the 78L09 is lightly better at 6mA), so your pedal would need an on/off switch to avoid running the battery flat quickly.
It's possible that your pedal would work ok from 12V directly, but without a schematic we can't be sure.

 

[BobK]

Alec_t,

He is running it off a 12V adapter, not a battery.

Bob

 

[Alec_t]

So he is.

 

[Pharaday]

Actually, I have only ever run it off a 9V battery OR, recently, off a 5V adapter. It works on a 5V adapter, but not as loud and speed doesn't go as high. I agree that it would probably work off a 12V adapter, but I'm afraid to try. I've blown things just trying willy nilly like that. It's a FAB flange, S/N: 7010909522, if that helps. I can post a pic of the circuit boards, would that halp?

 

[Alec_t]

Why not buy a 9V adapter? A couple of diodes could then be used to steer power from that or the 9V battery as required, or a switched jack would do the job.

 

[davenn]

I answered this in post #2

thread closed