adapting an ac adapter

[christobean]

i have several ac adapters from old video games and stuff, but they are all for 4.5 or 6 volts
is there any way i can mod them to run 9 volts for a stompbox?
thanks

[Joecool85]

Not easily.  I am looking into buying a sega adapter at radioshack and modding it for pedal power supply though.

[Paul Perry (Frostwave)]

If it was an emergency, and you were on a desert island or something, you could put the outputs from two 4.5V adaptors in series, like they were batteries, to add the voltages together. I don't recommend it, but you can do it if you want.

[christobean]

are there any other options for making a power supply without buying a transformer?

[Joecool85]

Yes, if you mean not a regular transformer.  You can buy adapters.  Like the one you have, but different voltages.  You could use a 9vAC adapter, rectify it and regulate it.  Or you could buy a 9vDC regulated adapter and you're done, if its noisy, make a small box that holds a 2200uF cap that goes from + to ground.  Or buy a 12vDC unregulated (or larger), and regulate it down to 9vDC.

Of course, if you can find a transformer out of a junk radio or something you are all set too.

[R.G.]

i have several ac adapters from old video games and stuff, but they are all for 4.5 or 6 volts
is there any way i can mod them to run 9 volts for a stompbox?

Yes, maybe.

Is the output for AC or DC? If it's AC, you can do a voltage-doubling rectifier and get enough volts to run your effects.

If the voltages are DC, you can, as Paul notes, stack them until you get over 11V and then run a three terminal regulator.

I don't know what part of the world you live in, but here in Texas, there are so many wall-plugin adapters that one from some other application can usually be had for almost free. At worst case, the thrift stores will often have a basket of them for a couple of bucks a piece.

[smallbearelec]

i have several ac adapters from old video games and stuff, but they are all for 4.5 or 6 volts
is there any way i can mod them to run 9 volts for a stompbox?
thanks

While it could be done various ways, as others have pointed out, it seems to me like more trouble than it's worth. Depending on what you want to do and how you want to build, there are two inexpensive transformers and a few designs that you should check out:

--The Mouser 41PG006 has been used for a long time. It's 12 VCT, only 60 ma. out, but it's dirt cheap. If you want something with multiple isolated outputs like R. G.'s Spyder at GEOFEX, it is fine. I also used it as the basis of a low-current, tweakable Small Wart.

--I had always wanted a compact flat-pack transformer like the Magnetek FP12-200 that didn't cost a fortune, so I got one made. That's the basis of the Small Wart 200.

http://www.smallbearelec.com/Projects/ProjandProd.html

Regards
Steve Daniels

[Joecool85]

I should know this, but how many ma does a "normal" overdrive/distortion use up?

[Steben]

Look at the schematics, you'll be quite safe with these thumb rules:

Discrete OD circuits:  1ma/transistor.
Op-amps: 5ma/amp (not per "op-amp chip", per single amp in the chip!) , although there are opamps drawing less current than a transistor and some that draw double as much (10ma or more).
BBD's and Digital chips: at least 30ma/chip.
LED: 5ma.

A supply with 60ma is quite fine for OD/distortions (mostly too much). For delays and modulators, go for at least 200ma for most pedals.

[Joecool85]

Doesn't an average LED draw 20ma?