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DIY Stompboxes => Building your own stompbox => Topic started by: smallbearelec on September 23, 2004, 11:27:18 PM

Title: Better Small Wart(s)
Post by: smallbearelec on September 23, 2004, 11:27:18 PM
I made a couple of mechanical changes to the low-current Small Wart to address issues that had been bugging me. We know that nobody wants to have to open the thing to tweak the output, so I'm using "semi-fixed" trimmers from Mouser. I re-designed the board so that they poke out the bottom:

http://www.smallbearelec.com/Projects/SmWart/bottom.jpg

The precise spacing of the holes on the perfboard makes it easy to get accurate registration. Check out the revised article for details.

I also changed to a taller rubber foot so that you don't have to hack the shaft of the power switch.

It's now easier to build, and easier to use as a tweaker's tool--even when gigging.

I have the high-current version almost done. The big issue (other than getting everything on the board and in the case) was current limiting. To handle that, I have successfully tried on the bench a Bourns resettable fuse. I'll be getting together with Howard Davis next week to test a prototype.
Title: Better Small Wart(s)
Post by: RDV on September 24, 2004, 08:11:15 AM
Why would you want to make a higher current version(200ma I'm assuming with the flat-pack) and then limit the current?

RDV
Title: Current Limiting
Post by: smallbearelec on September 24, 2004, 02:40:42 PM
When dead-shorted, the high-current unit gets too hot. I want some device in there that will open up under really serious overload.
Title: Re: Current Limiting
Post by: RDV on September 24, 2004, 05:41:06 PM
Quote from: smallbearelecWhen dead-shorted, the high-current unit gets too hot. I want some device in there that will open up under really serious overload.
Like a circuit-breaker that trips when too much current flows?

RDV
Title: Re: Current Limiting
Post by: Peter Snowberg on September 24, 2004, 05:47:42 PM
Quote from: smallbearelecWhen dead-shorted, the high-current unit gets too hot. I want some device in there that will open up under really serious overload.

http://www.mouser.com/catalog/619/366.pdf 8) Look at the RXE series.

also available in axial leads and SMD
Title: Re: Current Limiting
Post by: RDV on September 24, 2004, 09:00:27 PM
Quote from: Peter Snowberghttp://www.mouser.com/catalog/619/366.pdf 8) Look at the RXE series.
also available in axial leads and SMD
I'm very interested in this Peter. When you use one of these, do you get one with the 'Hold' amperage rating of the value of your transformer? I hope I said that right.

RDV
Title: Better Small Wart(s)
Post by: Peter Snowberg on September 24, 2004, 11:28:57 PM
Pick the device based on the "trip" current.

The "hold" figure tells the draw you have to fall below before it resets automatically.

For a 200mA adapter, I would use the 650-RXE010 or maybe the 650-RXE017 but that later one is a little big. You have to be sure your transformer supplies the trip current when dead shorted. Some transformers just won't supply current beyond a given point.

There are lots of other resettable fuses. See the 650-TR250-120 or the 650-TR250-145 or 652-MFR010 or similar. They're all under "resettable fuses" :D

One thing to keep in mind with these devices is that they start out like a very low value resistor and after their first trip the values raises a bit. ;)
Title: Better Small Wart(s)
Post by: RDV on September 25, 2004, 10:48:22 PM
I forgot to ask the obvious silly Q.
Do you just put it inline with the DC positive?

Thanks in advance.

RDV
Title: Better Small Wart(s)
Post by: Peter Snowberg on September 25, 2004, 10:51:39 PM
Yep. :D

Not a silly question at all. :o
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