Evolution Of A Power Supply Idea

[smallbearelec]

Everybody here knows that the standard nine-volt 200 or-so milliamp wall transformer that sells for about seven bucks at Wal-Mart is only useful for powering pedals if it is front-ended with some additional filtering and, preferably, a regulator IC. COnsequently, I have taken a couple of cracks at designing a small power supply, optimized for use with FX.  A fair number of people have built my Small Wart 200, but that remains a suitable project only for someone who has good construction chops.  My version of the Small Wart 60 in the plastic case is mechanically simpler, but it doesn't deliver a heck of a lot of current, and that Mouser transformer is a little inconvenient to mount in a small case.  I have come up with something that delivers more juice but is easier to build.

Part of the good news/bad news of "success" is that you don't always have to search for things to buy; in time, manufacturers will often come to you and offer to sell you things.  Usually the advertising is of the "throw it against the wall and see if it sticks" variety. But sometimes, someone actually looks at your business and markets a product or products to you sensibly. A Chinese manufacturer e-mailed me their catalog, and I found this 12-volt transformer:

http://www.smallbearelec.com/Detail.bok?no=1012

It's 125 ma. output, PC board-mountable and a little more than one cubic inch in size.  So I

ordered samples and built with it what you might expect--a Small Wart  125.



It's what I said: the equivalent of a DC "brick" transformer, but quiet, regulated and current
limited. It has an on-off switch, an in-use indicator and a detachable line cord.  If you're
willing to build it yourself, it is inexpensive enough that you can easily afford several--use
them to avoid ground loops, do "dead-battery" simulations and accommodate positive-ground pedals. The construction is much easier than either of my previous Small Warts, and I have selected components and designed to eliminate metal hardware both inside and outside.

I sorta want to manufacture this, but the thought of getting a mold made so that I don't have to use an off-the-shelf Hammond case is a little scary. Of course, I will post a project. Has to wait a little, because I am out of medium perfboards and Mouser is back-ordered on that nice, inexpensive Cherry rocker switch. I also want to design a PC board for it.  Meanwhile, the transformer alone is available for purchase for use in Spyder-type designs.

Regards
SD

[R.G.]

Neat project Steve.

The transformer appears to be a knock-off of the Pulse Engineering EI130 series of potted transformers. I ran into these at Mouser when designing a remote AC-powered pushbutton for my NAS server. The ones I saw were only rated at about 20ma, so they're a lot more limited in current and your price for a capable device is great.

If you do your own, I suggest getting a couple of 100ma secondaries in there instead of one. That lets you have two isolated outputs instead of one, and the transformer price should be about the same.