Rants, raves and stuff from this dude's brain

This is going to be a quick post.  I just finished putting together a CMoy amp.  This is something I’ve been working on for a while now.  There’s a great tutorial on-line with parts list and everything if anyone wants to give it a go.

I had tried it once before but, my general stupidity when it comes to actually electronic parts led me to make a bunch of mistakes.  Stuff like capacitors really really really care about polarity.  Or if you don’t solder stuff properly electricity won’t flow.  So, as you can imagine, the thing didn’t work at all.  Not even the little LED.  Sadness.

I tried it again and this time with a little more patience and a lot more careful-ness when soldering.  And it works!  I kind of wish I would have take a couple of pictures before it was in the case.

If you look closely you can see I didn’t add a volume knob.  The reason is, this is going to sit between my iPod and the car Stereo.  I already have volume control on both devices, I didn’t need a third.

So I gave it another go.  The first try didn’t seem to go as smoothly as expected.  This time I tried using a jackhammer to drive  a nail (live action video at the end of the post).  I’ve recently gained access to a 60 Amp plasma cutter owned by the good people at TechShop.

(If you don’t know who they are or what they do, this this is a short aside.  Think of it as a gym for geeks.  You get access to all the tools you can possible imagine to make any project you can think off.  They have plasma cutters, metal benders, sowing machines, wood-working gear, etc, etc.  I highly recommend you join if you live near an area where they are located.)

For this I sat down and measured all the parts that are penetrating the case and did a very simple CAD drawing with Cut2D as well as made the tool paths.  Once I got the design dialed in, I took the the file and fed it into the Torchmaster driver software, made sure everything was aligned and zeroed properly and let-her rip.  I initialy used the speed for the machine straight from the operations manual, 155 inches-per-min (ipm).

This is what I got from the first try:

Not bad but looks ever worse that what I did by hand!  Ugh, so that didn’t work.  I looked around the internets for a while and found people saying that you should run the machine slower if the cuts are jagged and not precise.  Ok, so I ran the machine at 140 ipm.

This is what the second, slower, try came out as:

Oh noes! It was going so slow you can even see it get snagged on the top tube hole (right above the number 2).  As well the hole for the power-plug didn’t get cut properly.  Probably it was going to slow so the slag from one of the holes melted on to the part that was supposed to fall off (bottom right).

More internet search and some conversations with people at TechShop we decided to get a new tip and try and go quite a bit faster.  The final run was at 190 ipm.

Here it is try:

I don’t know how much better this was.  The lines look better defined but still, I’m not getting anywhere near the precision I need to fit parts in to this thing.  After staring at all 3 tries for a while it does seem clear the right side of all cuts are quite clean while the left ones aren’t.  This is quite clear when looking at the large circle cuts on the left (those are where the tubes are going to go).  My guess is the torch might not be level.  This is a brand new machine at TechShop so I’m sure there’s kinks to get out.

What did I learn?  Maybe using a Plasma cutter for this might be too big of a hammer for something so delicate.  Next step, CNC routing.  Stay tuned.

Ok, this is the Plasma cutter creating the 1st run.

As of a couple of week ago I’ve been getting the parts together to build my own tube headphone amplifier.  More information on the circuit and construction of the amp will come soon.  For now I just wan to share what I went though to get the box ready for the parts.

The part I’m using is from Antique Electronic Supply and is a 20 gauge steel box (Model number P-H1441-12).  I really can’t describe how unprepared I was to deal with this box.  20 gauge steel is hard metal to work with if you don’t have a garage full of tools and, I don’t have a garage full of tools.  But I’ll get to that later.

Here’s the box on my desk.

The first thing I did was mark the holes for the 3 tubes I’m using, power plug, RCA connectors, power switch and the hole for the cables from the transformer.

I found many websites that said the best way to do this was to use a drill-press.  I don’t have one and don’t know anyone that has one either.  That idea went out the window.  The next thing I tried was to drill a hole and then go at it with a cutting disk on a rotary tool.  This failed miserably.  Two broken disks later and I had barely put a dent on it.  Then I found this tool called a nibbler.  It’s an insanely brilliant tool.  Cuts though this metal like a hot-knife through butter.  It does this a couple millimeters at a time (get it? it nibbles).  I tried to clean up the mess I made with the rotary tool with the nibbler.  It’s the messy hole on the left in the pic.

After some more trial and error I did learn that going counter-clockwise with the nibbler is much easier.  The nibbler has a little tooth on the right side.  It uses this to begin the cut.  When I tried cutting clockwise this tooth didn’t catch and the tool slipped.  Once I figured this all the square holes were a breeze.

The round holes for the tubes weren’t that easy.  It just took a lot of patience with the nibbler and very little bites.  I stopped caring about the jagged edges left by the tool and figured out I could sand them down later.  This turned out to be true, which was a great relief.

This is the finished box with the round holes for the tubes.  The holes aren’t perfect, but this should all be covered up by the bezel that holds the tubes in place.

That was a lot of work.  Now, next step, install everything and wire it up.