Great tonepad power supply

[oldrocker]

I just finished it and it seems to work great.  I took apart an old wall wart and used the transformer and the four rectifier diodes and the 1000uf cap out of it.  The transformer is a 120 volt to 15 volt step down.  It says it was a 12 volt although I measured around 15 or 16 volts.  I set the 1k trim to about 8.89 volts.  The rest of the circuit was perfed.  I still need to figure out what to use for an enclosure.  It needs to be metal so I'll have to dig up something.  Nice regulated power supply.  I hope to use it to power my now battery only powered pedals after I get some DC plugs installed in them.

[smallbearelec]

Note Francisco's comment:

"An external 12V AC wall wart can be used to avoid the risk of working with 120v wiring. Use extreme care with wiring."

The board is clearly intended to be used that way. If you change the essential design and put the whole thing with transformer in a metal enclosure, do your homework and plan very carefully how you will handle the power input, safety ground, and the mounting and tying down of every component. See my articles on the Small Warts for some ideas on these points:

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

Regards
SD

[oldrocker]

Thanks Steve.  Yes I will check out all that you mentioned.  To be quite honest this build did make me a little nervous and I was thinking I had better do some more research for safety reasons.  I hope this will work for me or I will be buying stock in 9 volt batteries.
http://www.logmonster.com/images/full/?pic=ps1_1184213787-422-15262.jpg

[oldrocker]

I tried the unboxed power supply out after adding a DC jack to my Hwy89.  So far so good.  I need to add more plugs coming from the PS to power multiple pedals. The Hwy89 sounded fine and it was nice to be able to leave the pedal plugged in without worrying about the battery draining.
http://www.logmonster.com/images/full/?pic=ps25_1184271493-422-15277.jpg
http://www.logmonster.com/images/full/?pic=ps24_1184320850-422-15276.jpg

[Processaurus]

an ABS enclosure would be perfect, they are really strong, but are light, and easy to machine (especially since you'll probably need a square hole for the AC line jack.  Plus no worries about the ac getting on the metal box.

[smallbearelec]

an ABS enclosure would be perfect, they are really strong, but are light, and easy to machine (especially since you'll probably need a square hole for the AC line jack.  Plus no worries about the ac getting on the metal box.

True...and you can even do it with a two-wire line interface, IF you are VERY careful not to have ANY metal fittings penetrating the case that could accidentally become electrically hot. I used nylon hardware in some critical places when I did a low-power Small Wart this way.

One other concern is whether that transformer is the kind that automatically limits current under short circuit conditiions. I don't know how to tell whetherit is, and you may want to get advice from other people on this point. If it is not, you should put a resettable fuse between the filtered DC output and the input of the regulator. The LM317 and similar chips protect themselves in a short-circuit condition, but some means of current limiting is needed to protect the transformer from overheating. Again, see the Small Wart schems and construction notes.

[oldrocker]

Thanks gentlemen.  I will take all of this into account.  I noticed the fuse used is a resettable 50ma hold.  I'm hoping this will be OK for mine.  I will do more research and get more information before I finish this and start using it on a regular basis.  I noticed after about an hour and a half that the transformer was warm but not too bad.  I don't want to take chances though and with a power supply I want to be very cautious and careful.