Random DIY

[mshilarious]

I have a bunch of small DIY projects I'm trying to finish up in the next few weeks, I'll post some of them here.

Here's something really basic that might encourage somebody--this is a 12VDC power supply in a 1u rack case. I used a commercial switching power supply, so it's not true DIY, but a good switching power supply is not really DIY.

The great thing about switching power supplies is better than 90% efficiency and excellent regulation. The downside is the potential for switching noise to leak into audio. This supply reads a dead 12.00V and 3.5mV of ripple. I haven't scoped it, but clearly this would need more filtration to be used in an audio circuit.

And that's OK, because it's in its own box, and any audio circuit really ought to have local regulation and filtration anyway.

In fact, I built this box as a power supply for the pipe organ I've been working on now for . . . uh . . . 18 months. I need a pretty good amount of power for it, this just switches the electromagnetic valves on and off, at 130mA a pop. This is a 15A supply, so in theory I could play 112 pipes at one time; I'd be happy with less than half that, as I only have about 230 pipes . . .

OK, back to the DIY: real simple, a hardwired AC plug (to avoid needing an IEC punch) into a switch (with integral 12VDC LED), a 4A circuit breaker (so I never have to replace the 15A fuse on the board--why would a 12VDC 15A supply have a 15A fuse at the 120VAC side ), into the power supply. 12VDC comes out into two Speakon connectors (for the pipe organ), but also two 2.5mm AC adaptor style jacks, one front and one back, so I can run random stuff off the same supply. Also, there is a fan to help cool the supply and the power LED that also run off the 12VDC supply.

Nice and simple, a $30 Mid Atlantic 1u box, and my trusty pair of step bits for drilling. The drilling was very ghetto, normally I print out a design template and tape it to the box to keep things lined up, but for my own stuff I don't care. You should see the box top where I drilled vent holes randomly!

If you don't already have a step bit, buy one tomorrow. I weep when I think of all the DIY years when I didn't have a step bit

 

[antichef]

(to avoid needing an IEC punch)

...

If you don't already have a step bit, buy one tomorrow. I weep when I think of all the DIY years when I didn't have a step bit

a step bit like these?

http://cgi.ebay.com/28-size-3pc-HSS...5|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

and what's an IEC punch - something else you'd use to put a hole in the rack metal in addition to the step bit?

(and thanks for all the knowledge disbursements, btw )

I think I'm going to have to build an external power supply for my long festering rack mounted DMP2 project.

 

[mshilarious]

a step bit like these?

http://cgi.ebay.com/28-size-3pc-HSS...5|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

Yep, although I just bought mine at the local hardware store. I would get a bit that goes all the way to 1" though--standard chassis mount XLRs are 15/16".

and what's an IEC punch - something else you'd use to put a hole in the rack metal in addition to the step bit?

Yeah, you can get punches to cut holes that aren't round. I have a couple of Greenlee punches, but I never use them anymore. I should sell them . . . anyway, the other options are a Dremel tool, or a file and the rest of your life . . . or a milling machine . . .

 

[sweetbeats]

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96275

Picked these up last week to go with my original step-bit...I've got a project coming up to build power supplies for my old Radio Shack PZM's. Gotta drill for jacks in an aluminum case. Step-bits are a life saver. You have to be a little careful of drift when free-hand drilling in softer materials especially (plastic or wood), but they make quick work of drilling clean holes.

Essential DIY gear...

 

[dgatwood]

and what's an IEC punch - something else you'd use to put a hole in the rack metal in addition to the step bit?

An IEC punch would be presumably a punch for a C14 chassis socket (commonly used for electrical plugs). It would make a hole that's roughly rectangular with rounded corners.

Normally, when you use punches, you drill a hole first. You then run a bolt through one part of the punch, then through the hole in the material, and finally into the other part of the punch. Next, you tighten down the bolt by thumb until the sharp blade-like protrusions on the back side of the punch dig into the material sufficiently that the assembly doesn't rotate easily. Finally, you take a wrench and continue to tighten the bolt. That bolt effectively pulls the outer part of the punch into the inside of the inner part (or vice-versa, I forget which), thus behaving like a giant, shaped pair of scissors.

As for myself, I've only attempted an IEC connector once, and I did it with a circular drill bit and a small file. It took a small eternity, but it didn't cost eighty or a hundred bucks like my XLR punch did, either....

 

[mshilarious]

More random DIY: XLR-o-scope!

Here's something I wish I had a long time ago--the XLR-O-Scope! I can't really afford a decent O-scope, and they are waaaay too bulky, and software is really better at analysis . . . so . . . using my opamp microphone circuit, I created this instead!

Pretty simple . . . I used a low-current opamp as the first 2/3s of an instrumentation amp, with a 10M input impedance. This is kinda similar to what you see here on pg. 12:

http://focus.ti.com/lit/an/sloa058/sloa058.pdf

Except the mic preamp acts as the differential amp after the high-impedance buffer.

Limitations: well, between the chip, the mic amp, and the converter, you're not going to do better than 100kHz resolution. That's OK, usually I just run at 96kHz, which gives me 40kHz resolution. I normally am just interested in AF distortion, power supply ripple, stuff like that. It is AC coupled, so it won't show DC at all. That's OK, I have a multimeter. I'm a little worried about the inputs, because this is a sensitive chip (it will be quickly destroyed by hot-patching phantom if you leave out D1-D4). In my mics, the input is a hardwired electret capsule, so no worries there. I will just have to be careful what I test--usually something else phantom-powered anyway.

Sorry my camera does a crummy job at macro . . .

 

[mshilarious]

This is the coolest DIY ever!

This is going to be featured on several upcoming projects, definitely the Fender So-Cal featuring Brian Wilson Presents Smile sticker guitar, and also another idea I've been kicking around for an all-class A JFET/MOSFET guitar amp, using a tube-style topology--complete with output transformer! It will need the mojo from the chicken, which will cause guitarists worldwide to throw their chicken-less tube amps in the trash!