Calling this an amplifier build would be deceitful

Its more of a box build.

So browsing adafruit.com a while back I came across a class-d amplifier board they recently introduced. What is interesting about class-d amps is they are very efficient, thus generally needing no heatsinks. Seeing boards like this I am frequently reminded how far things have progressed since my electronics classes in 92/93. In that class I tried to build an amplifier for my car, and really didn’t get much further than etching the board. The traces didn’t etch cleanly, even using the advanced (at the time) sharpie+acid method. After getting board patched up with jumper wires to fix screwed up traces I then realized how expensive power mosfets were for a high school student. End of that project.

So I of course bought this little amplifier board immediately. There has been some conversations around the house that we should have music upstairs. So this board + an old ebay purchased airport express should do the trick nicely. So board in hand, it needed a box. I always skimp on the box, but in this case the board was pre-manufactured so I could afford to put some energy into its home. I haven’t done anything with any hardwoods on the CNC yet, and I had some walnut I got from a friend when he moved. So I set about making a box.

I have no jointer, so surfacing with the CNC, using a 1″ bit.

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Flipped the board over and routed a box + lid.

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The lid didn’t fit perfectly, and required some chisel work on the inside lip to seat properly. The outside also needed some time on the disc sander to be flush all the way around. I really need to upgrade my y/z axis with some linear bearings. Maybe this winter.

With the overall box built i used the drill press to put some holes in the back to mount the 1/8″ input, the 12v barrel jack, and the 4 speaker posts. Of course one of those holes is a square, so I had to spend some time with the files.

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Before mounting anything I needed to finish the back, as it would have been hard to do with all the posts etc in place. I was just going to do a basic coat of poly as this wood was very nice. Got out the rattle-can and gave it the first light coat – which did not work out well. I was not paying attention and grabbed black spray paint instead of my clear lacquer. How could that happen?

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Quick wipe down with mineral spirits, but black was deep in the pores. Decided to just blast the whole thing with black, wipe with spirits, and sand again. Turned out ok, gave the wood a darker appearance – although this wont be my ‘go to’ finishing technique.

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Mounted the amplifier inside with double-sided foam tape, and soldered up all the connections. Pretty basic.

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Functionality test with a 12v 1.5A switching power supply I had in the junk box, and it wouldn’t power up. I kinda forgot that 20w per channel is 40w. At 12v you need 3.5A at full power. I tested instead with a 11.1v Lipo battery from one of my RC airplanes, using alligator wires to the board and all was fine. (fatal mistake)

Double checked everything, glued the lid on, and finalized the finish.

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I sourced an old pc power supply, as they can handle crazy current, and modified it to work w/o a pc. Grounding green wire is all it takes. I pulled out all the un-needed connections and put a barrel connector on it.

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Brought everything inside, connected up the speakers, power, airport express… and it doesn’t work. Much testing ensues, still does not work. Shamefully bring it out to the garage, and bust it open with a chisel.

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Of all things it turns out the barrel connector plug was bad. That was why the initial power supply didn’t work. That is why new power supply didn’t work. The test battery worked because I alligator jumped the leads to the back-side of the connector. Dang.

So now the power supply is hard wired in and everything works fine. This amp does a great job driving bookshelf speakers, and i would use it again. Things I would do differently if i were to do this again (hint : i won’t).

    Not use black spray paint by accident
    Put an indicator LED in the box so I know if there is power
    Turn the box ‘upside down’ and inset a plexiglass bottom that is screwed in (for access)

Overall a fun project, and I learned how nice walnut is to work with. I also finished an amplifier project, that i started over 20 years ago!

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CNC sign from Plywood

My neighbor is starting to brew his own beer, which is a great boon to me.  In an attempt to curry additional favor I offered to make him a sign for his garage.  My intent was to do a trial run in plywood, then do a final in maple with walnut letters.  While doing a clearing operation the main portion of the sign, I got into a layer of plywood that had a very nice grain/color.  I am no real wood expert, so I don’t know what it is, but it was very pleasing overall.

Got off easy on this project, just routed the letters down into the next layer of lighter colored wood, and I was set.  Few coats of rubbed poly and off to the neighbors.

Lesson learned – look at the edges of plywood when routing, you may be able to use the various layers to your benefit!

New sign for the workshop

Took a shot at making up a sign for the workplace.  Learned quite a bit in the process, and wanted to document a few of those learnings for the proverbial ‘next guy’.

I used 3/4″ mdf.. and a 1/4″ upcut spiral bit to do most of the cutting.  The circle logo and ‘aperture’ letters are .4″ above the surface, and the ‘laboratories’ letters are .2″.  I profiled the letters after the overall pocket was created with a 1/8″ bit to get more definition.  This all worked ok except for a few things:

  • An ‘R’ and an ‘I’ in laboratories popped off.  The MDF doesn’t hold well when the letters get small.
  • I re-routed those letters and then glued them on.  In that process I realized that NEXT time i would just route all the letters out of another (thinner sheet) and glue them on.  It would save many hours of pocketing work.
  • Glueing the letters would also allow for easier painting as you could paint everything seperate and then glue them on.
  • On the topic of paint, for $3 for a 1/2 quart home depot will create color matched ‘sample’ paints… awesome for this kind of work.
  • Be careful when shopvaccing around the machine while its working.  At the end I looks like a skipped a few stepper moter steps on the x axis, so i have some rough edges on the right side of my letters.  I vaguely recall the router pinching the hose against a letter while vaccuming.. that may have caused it.  If it didn’t.. well thats a problem for another day.

So I learned a lot, and have a fun sign for the garage – its about 36″ long for reference.

Dust seperator for the CNC

I have a love/hate relationship with MDF.  It sure machines nice, and paints well if you seal it with watered down glue first.  But the DUST!  My 5hp shopvac has a steady reduction in suction as the filter clogs up.  It’s capacity is noticably diminished only 1/2 way into a machine run.  I have been looking at Bill Pentz’ cyclone page for a long time, with dreams of building one.  Sourcing of the metal, room in the garage, and downright dislike for sheetmetal cuts has dissuaded me from going down that route (thus far!).  I recently came across the ‘Thien Separator’ which in concept seemed like a good comprimise.  Didn’t look like it would take long to make, could be adapted to a shopvac/5 gal bucket and had nominal sheet metal work.

So, with that in mind grabbed a bucket, a caliper, and my mouse and drew something up.  Initial design didn’t take long to get drawn, and over a couple of days I made minor tweaks until I got a chance to run it on the machine.

Clogged the shopvac BTW.

So you can see the pieces outlined, from the first run.  Piece on the left is the bottom of the bottom.  You can see the 120 degree cutout, the bucket groove, holes for bolts, and the profile cut.  On the right is the bottom of the top.  Groove for the sheet metal, and a hole for the outlet to the vaccuum.  Along the top are the risers which mount the incoming line (it’ll make more sense in a later pic) and an aborted ring made to support the outlet.  I hit the y-axis limit switch, and had to redo that later.

I pulled the pieces and cleaned them up.  I then also machined a 1/8 groove in the top of the bottom piece which was needed to receive the sheet metal (not pictured).  Below you will see a picture of the bottom sitting on the bucket.  You can see where the incoming material will circle around, and fall into the slot – landing in the bucket.  At least thats the plan!

For the sheet metal, i picked up a roll of 10″ galvanized flashing.  I trimmed it down to 8.4″ (8″ + two 1/4″ slots + wiggle room).  It was pretty thin (not sure what gauge) so I cut two pieces and doubled them up.

Pretty straightforward assembly from here.  Work the metal into the 1/8″ slots, sandwich the top and bottom.  Tighten the threaded rod.  Insert the inlet blocks, and glue them in.  Silicone around the edges.

Here is a picture of the final product.  I am going to test drive it with a garbage can liner in the bucket, as it would make disposal real slick.  Right now the seperator sits on the bucket with a friction fit, and with the vaccuum on i don’t detect any leaks.  I will post updates on effectiveness after my next CNC run, but a quick cleanup of the dust on the floor, shows most of it ends up in the pail!

EDIT:

Ran the system on both the CNC and the Tablesaw today, and the seperator worked swimmingly!  Nothing of note in the shopvac, about 4 inches of dust/shavings in the bucket!

Wine bottle ring

I had a friend turning the big 4-oh and he was having a little dinner event.  I was bringing a bottle of wine, and as he thinks the CNC machine is pretty cool I wanted to make him something.  As my wife indicated all the birthday cards we had in the house were too girly, I thought a ring of some sort on the bottle would work out nicely.

I broke out he calipers, and measured the neck on a bottle I had in the house.  Pretty straighforward to draw up the ring in CAD, and add the text.  This was my first text engraving, and all I had on had was a 60 degree v bit I had purchased for isolation routing circuit boards (which I haven’t actually done yet).  I loaded up some maple on the CNC machine, and put a piece of contact paper (for lining kitchen drawers) on it.

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I then routed the text, and blasted the letters with some black spraypaint.  The contact paper made a great mask.

I then routed out the circles, and did a light sanding on all sides.

One note, be aware not all wine bottle necks are the same size.  We ended up taking the ring to the wine shop, and had to test bottles to ensure it fit on the one we purchased!

Machining trays for WarMachine mini’s

So this is a peek into my really dorky side.  The general idea is a needed a tray to transport my mini’s from the kitchen counter to the game table.  The end result is much more complicated than it needed to be, but i learned a lot in the process.  One of which is you probably shouldn’t use the old 1/4″ bit you’ve had for 8+ years for moderately fine work.  The other is how hard maple is to plane/join.  I have never actually worked with a real hardwood before, so that was fun.

Video of the process.

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Monitor mount for CNC machine

I needed a to replace the stock monitor mount on my 19″ lcd as the base took up too much room, and didn’t leave any for the keyboard.  The VESA mounts are standard 70mm spacing, so it was pretty easy to draw up a replacement.  The only thing I forgot to account for is the on/off toggle on the back, so I had to add a notch for that during install.

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