The Small-Wart 125

smallbearelec · September 12, 2010, 09:06:52 PM

Not long ago, there was a post here asking what would be the "best" power supply for pedals. My answer is that what is "best" depends on what you need. If you have a large board, no problems with ground loops and no positive-ground pedals, one high-current supply (One-Spot, BOSS, Voodoo Labs, etc.) will do you fine. In some situations, though, you just want the equivalent of a wall-wart (or maybe more than one), but stable and well-filtered. That's my Small-Wart 125:

http://www.smallbearelec.com/Projects/SmWart/SmWart.htm

I had shown my first prototype a while back, but I wasn't happy with the amount of prep needed on that Hammond case. This version can be built in two evenings without hurrying. The circuit is nothing new to anyone here, but this project has always been more about mechanical design and details; I am very happy with this version and hope you find it useful. The full kit is available on the Stock List.

Regards
SD

askwho69 · October 21, 2010, 06:30:42 AM

is this power supply as quiet as GGG's?ultra quiet? even though its not using metal cases?

anchovie · October 21, 2010, 07:39:10 AM

Metal cases are important for audio signals, not 9VDC power. Ever seen a metal-cased wall-wart?

Gus · October 21, 2010, 05:29:46 PM

You are going to sell an AC plug in the wall kit to people that might have problems building a 9VDC battery powered effect?

Where is the transformer AC in fuse? You are going to plug that in the wall with no AC fuse and thermal protection. IIRC wall wart have thermal fuses and transformer wall side fuses.

IMO The deluxe is missing two diodes to protect the 317

IMO The first one is missing one protection diode for the 317.

No heatsink on the TO220 package?

smallbearelec · October 21, 2010, 09:32:03 PM

Quote from: Gus on October 21, 2010, 05:29:46 PM
You are going to sell an AC plug in the wall kit to people that might have problems building a 9VDC battery powered effect?

Anyone who offers a power supply design of any kind has this issue. There is self-selection involved, and I do my best to discourage the inexperienced.

Quote from: Gus on October 21, 2010, 05:29:46 PM
Where is the transformer AC in fuse? You are going to plug that in the wall with no AC fuse and thermal protection. IIRC wall wart have thermal fuses and transformer wall side fuses.

That transformer draws almost no primary current. The smallest fuse you can buy stands a chance of not popping under short-circuit conditions. I tested this during design, and I went with the resettable fuse.

Quote from: Gus on October 21, 2010, 05:29:46 PM
IMO The deluxe is missing two diodes to protect the 317
IMO The first one is missing one protection diode for the 317.

Are those mandatory when a resettable fuse is used?

Quote from: Gus on October 21, 2010, 05:29:46 PM
No heatsink on the TO220 package?

I have tested the short-circuit protection repeatedly. Since the transformer is only rated for 125 ma. and the resettable fuse kicks in at about 150 ma., the IC does not get dangerously hot even when the output is shorted. By all means, try one of these yourself.

askwho69 · October 21, 2010, 10:03:04 PM

WOW! U like this! smallbearlec has all the answer!! but i think this power supply hums? because its not in metal chase . . .but if we use 100r and 100 uf will ease the hum?

smallbearelec · October 22, 2010, 12:12:34 AM

Quote from: askwho69 on October 21, 2010, 10:03:04 PM
but i think this power supply hums?

No. It has far more filtering than you get in any wall wart, and the three-terminal regulator chips are specifically designed to eliminate hum.

askwho69 · October 22, 2010, 01:15:52 AM

ok this is nice i'll make this one

Gus · October 22, 2010, 05:41:37 PM

http://www.national.com/ds/LM/LM117.pdf
page 10 for the two diodes.

smallbearelec · October 22, 2010, 06:30:46 PM

Quote from: Gus on October 22, 2010, 05:41:37 PM
http://www.national.com/ds/LM/LM117.pdf
page 10 for the two diodes.

Thanks for the reference. It states:

"No protection is needed for output voltages of 25V or less and 10μF capacitance."

If I ever do tackle a higher-voltage design, I will be aware of this issue.

SD

Lurco · October 23, 2010, 03:02:55 AM

Quote from: smallbearelec on October 22, 2010, 06:30:46 PM
Quote from: Gus on October 22, 2010, 05:41:37 PM
http://www.national.com/ds/LM/LM117.pdf
page 10 for the two diodes.
Thanks for the reference. It states:

"No protection is needed for output voltages of 25V or less and 10μF capacitance."

If I ever do tackle a higher-voltage design, I will be aware of this issue.

SD

the larger than 10µF cap will be rail to rail in the customers effect!

stringsthings · October 25, 2010, 12:18:55 PM

Quote from: Gus on October 21, 2010, 05:29:46 PM
You are going to sell an AC plug in the wall kit to people that might have problems building a 9VDC battery powered effect?

hey Gus, i think your comment would be more appropriate on the "Don't-Electrocute-Yourself" forum ... ICYHN, DIY stands for "Do-It-Yourself"

or, you could contact your nearest Television Manufacturer about putting warning labels on the back of their sets ... something to the "effect" of:

Warning! Beware of Danger! This TV comes with an AC plug!

Gus · October 25, 2010, 06:12:40 PM

It is all about liability.

I have been building for decades. I have seen things other people have built. This is one reason I have not sold kits or even PCBs for things like external powered tube and transistor condenser microphones.

The big question is what is the liability of selling a kit of parts for a device that plugs into a AC socket? It might be one thing to sell parts and another a kit of parts.

Stringsthings I don't know if your is post is for humor or if you think my posts were a waste: however liability is a big issue in the USA IMO.

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The Small-Wart 125