making a regulated PSU out of a wall transformer

[DiggyFresh]

Hi peeps,  apologies for my english and if this topic shouldn't be here but i think it applies.


I'm thinking of using the transformers inside cheap "wall wart" transformers to make better, regulated power supplies, is it a good idea?
Like using just the transformer, adding a fuse, power switch, new rectification, a regulator and good filtering.


Because finding a transformer with the right specs is hard here, and some of these cheap wall wart already have right speced transfos. Like a 9v one would probably be good
with filtering and regulation ect..  i assume it probably would be 200% better than just using the adapter like it is.

Should i just forget it cause they are too cheap ? And just order a "better" transformer?

thanks

[merlinb]

You could build a little box that allows you to plug in any wall transformer that provides 9 to 15V AC, or 12 to 15V DC (or even higher). It then rectifies and regulates this, ready for pedal use. No need to take the wall transformers apart. I did exactly this, and it's very useful since I can always find a wall wart in the that range somewhere in any building.

[smallbearelec]

Hi--

You are thinking straight, as what you describe is common practice to "clean up" a wall wart for stompbox use. If possible, I would start with one that has a 12 Volt DC output. That will give the regulator room to "swing." You don't need to add a fuse, because wall warts necessarily have some form of short-circuit protection built into them. Find a small enclosure; plastic is OK for currents up to 150 ma. or so.

http://www.smallbearelec.com/servlet/Detail?no=1014

Put power jacks on front and rear, LABELLED CAREFULLY so that you don't fry the internals.

http://www.smallbearelec.com/servlet/Detail?no=1362

Inside go a large filter cap, 7809 regulator, small output filter cap.

[DiggyFresh]

Thanks guys! I didn't think about this! Would be super easy and cheaper.

I found a good site that breaks down exactly what you guys are saying: http://www.dxing.info/equipment/wall_warts_bryant.dx


I guess the only advantage of building a complete PSU would be shielding of the whole circuit/transformer. I mostly use effects/keyboards in the studio so i might take this more
complicated route. Of course it'll be way more expensive, adding a IEC socket, a cord, a metal box ect ect...


I'm guessing a power transformer is just a power transformer , appart if it's buzzing or has a deffect, i guess it would be the same as if i used a normal power transformer right?


thanks

[DiggyFresh]

I'm looking for the Overkill route for the studio. 

I mean if it's well shielded in a steel box,  would i see a difference/improvement if say i used a good quality Toroidal transformer instead?
( if it's an exetrnal psu in a metal box)

i'm guessing the regulators would get rid of most of the crap and it would be the same. ( as far as my limited understanding)

Thanks for your input on this

[smallbearelec]

would i see a difference/improvement if say i used a good quality Toroidal transformer instead?
( if it's an exetrnal psu in a metal box)

Building with your own transformer, especially in a metal enclosure, makes this a Waaay more difficult (and possibly dangerous!) project, because you would be making your own connection to the AC power line. I would strongly suggest sticking with the wall wart solution.

[PRR]

> difference/improvement if say i used a good quality Toroidal transformer

That's good for when you must put the transformer CLOSE to critical audio circuits.

Keeping the power transformer AWAY from audio is even better, and is what wall-warts are good for.

E-I core (cheap) transformers are actually a wee bit better than torroids at rejecting some stray coupling from the wall-power into your system. (Torroids are better wide-band transformers; you don't *want* wide-band, you just want your 50Hz/60Hz power.)

[greaser_au]

The nice thing about the wallwart is that is is a complete boxed device that has been type-approved by the electicity authority (or the UL/CE) so I'd expect that will be one less set of questions to be answered in the case of a problem. Plug it in and use the output however you like, you are safely isolated from the mains supply. There are no doubts or concerns about your own mains wiring.

I built my first pedal supply from a 16VAC 1A plugpack over 20 years ago.

david

[DiggyFresh]

Thanks for your input gentlemens.

Thanks all for the concern about safety, as it's surely not a project for the novice. I should have mentioned that i already built
several power supplies both internal and external for mic preamps and various things. I did my homework and i know all the safety rules.
But most of the power supplies i built before used nice toroidal transformers i ordered online. that's why i was asking about using the wallwarts transformers,
Cause they are availlable and very cheap.

@PRR thanks! Very good info. I will use normal E-I core in the futur if it's not inside the equipment. But Does the quality of the E-I core transformer matter much?
Would the one inside a wallwart be good enough? things like noise rejection ect? compared to an off the shelf E-I?

One of my concern about using a wallwart's transfo inside an external supply is probably just how to mount it,  as it would'nt have any bracket i guess. 

For the moment i'll try the "regulating box" idea, will be very practical for keyboard and stompboxes.

thanks y'all