[Predator88]

Well, I hate dealing with batteries when I don't have to (rechargeable or not). So for the cmoy i built, I find that only on occasion will I really use it for portable purposes. So I was wondering if there is a way I can make an external PSU for it (small and cheap is nice), but still be able to use the battery when I need it.

 

[diredesire]

Yes, just get a switched DC Jack and a small wall wart. Partsexpress.com has cheap wallwarts, you'll need one 9+v (depending on opamp and voltage tolerance of your parts) and mA requirements don't typically matter, as the CMoy is well under the maximum of almost all the wallwarts on the page. Make sure you match the diameter of the plugs on the wall warts to your switched DC Jack. They're typically 2.5mm or 2.1mm

Another way of doing it is wiring a molex connector for your computer PSU to a 9v battery snap. You can use either the +12v and +5v to make a 7v power plug (which is near the bottom of the requirements for a lot of opamps, but it will maintain it at a constant level). Or you can use +12v and ground for a 12v power supply.

The Computer PSU is supposedly fairly noisy, and isn't the most ideal power option, but for a CMoy i don't think it will make a large difference.

Good luck!

 

[Ikon]

You could use a cheap unregulated AC-DC wall-wart and build a simple regulator on a small board for it. A cheap LM78xx regulator IC (the "xx" stands for the output voltage) and 2-3 capacitors would already do, I wouldn't build much fancier things for a CMOY. The datasheet of the chip will give you an idea of the circuit (I strongy suggest also to use a protection diode, it costs only 2 cents but can rescue your amp).

Note, that more voltage means a higher voltage swing / less distortion for op-amps, most of them can work with up to 36V (respectively +/- 18V). The highest output voltage you can get with LM78xx regulator series is 24V (that would be a 7824 chip then) and I suggest that is what you should use. The regulator's input voltage needs to be at least 2V higher than it's output voltage, so your wall-wart should deliver at least 26V in this case. The input voltage can be even higher (up to 38V with the 78xx series), but beware that this will result in more heat (a heatsink is always a good idea for these regulators).

As you don't have to care about enough voltage with mains power, I wouldn't settle for a 10 or 15V supply here -> use the potential, it's definitely worth it. As for output current of the wall-wart, even the smallest 100mA thingie will be enough.

 

[ATAT]

The "Simple" solution

a TREAD + AC AC Wallwart transformer + DC Jack + Diode.

 

[leftshoe]

You can run a cmoy straight off of a 12v wall wart. Thats what I do, and I havn't had any problems so far. The solutions other people have suggested may be better, but I havn't tested anything else, so I can't comment on it.

 

[MisterX]

Quote:

Originally Posted by ATAT The "Simple" solution a TREAD + AC AC Wallwart transformer + DC Jack + Diode.

QFT.

 

[mono]

The typical unregulated AC-DC wall-wart is very noisey, too much so for a CMOY. Computer PSU is also quite bad, IMO. If you had a regulated wart, completely different situation but the typical generic wart is not regulated.

The simplest and cheapest thing I'd suggest is to grab any-random 12V wall-wart, any size really, I've never seen one with less than 50mA and that's enough for a CMOY.

Add to the output of the wall wart, on a piece of protoboard, air-wired, or however-you-wanna-do-it, 1 x 100uF capacitor across the +- input, an LM7812 regulator physically near it, and another 100uF cap after it. If you prefer tantalums, a smaller cap will work. This is only with a AC-DC wart, if you have an AC output wart you then need a bridge rectifier after it then far larger capacitor before the LM7812.

Next step up is an LM317 or similar adjustable regulator. Takes a minor bit of layout as you have double # of parts including resistors. Better performance but on a CMOY you may not care so much.

 

[Lithos]

I used this:
http://www.vellemanusa.com/common/pr...an=1&id=350481
and a AC to 24V DC Adaptor

 

[]|[ GorE]

Pretty Simple really.
Take a wallwart preferably one with a large value capacitor in it.
If it doesnt have a capacitor in it,atleast buy a 4700uF cap and wire it in parallel with the wallwarts output.Now you have got enough charge in the capacitor to remove the humps in the voltage output of the wallwart.

Next,Download the LM317 Voltage Regulator IC's datasheet.Implement the diagram for "Variable output voltage with extra ripple reduction".
DONE !
Oh BTW,
i got my LM317T for 20cents (USD).

 

[Predator88]

thanks for all the advice guys. I'll post resulting pics when/if i build it (realistically I will rarely use the cmoy outside of portable situations.). I'll chekc the ol wallet and see how its looking nowadays then decide (not that this is expensive but all the little projects can add up quickly).