hypofocus

In continuing the current theme of catching up on updates, that someone may read someday, I thought I’d post some pics of my attempt at a 386 amplifier.

This was a quick little project, a chance for me to start and finish something in a weekend and at the same time learn a new tool. First was to draw up a schematic pulled from the various designs and a large chunk straight off the data sheet. The schematic was drawn up in TinyCad.

I had hope to use this to export a netlist and play with a couple of layout/pcb type programs but fell foul of the lack of package attributes in the tinycad library. given that most of the time I’m not entirely certain what that’ll be until I scrounge up the part that wasn’t entirely helpful. Since then I’ve discovered an eagle library with the majority of the parts that I use.

Next step was the breadboard. I must admit at this point that my first breadboard circuit was somewhat messier and when I moved it over onto vero-board, tidying up as I went, I managed to get something wrong. I still don’t know what, the layout matched the schematic as far as I could tell, there were no solder bridges and the track breaks were correct. After much head scratching and probing I decided to rebuild it again on the breadboard in a layout that is closer to the final layout.

As much as I have an historical attachment to veroboard, I’d love to see some more of the American prototyping boards easily available over here. I did find one supplier selling the Radio Shack ones but I can’t find it again.

Here’s a photo showing the completed construction. The speaker came out of an old Acorn computer that had suffered fatal battery leakage and the jack is a standard Neutrik part.

Finally the project needs to be put in a case. Traditionally these amps are housed in a cardboard cigarette packet but i had a better idea. At a festival I was working on last year Lambert and Butler had the exclusive rights to sell on site and were selling cigarettes in these wonderful metal tins. Of course metal tins are conductive where cardboard is not. So a healthy dose of heat-shrink is wrapped around the circuit and the jack socket. The speaker mount was cut somewhat erratically with my budget powered multi tool, the speaker was stuck in place with an adhesive I normally use for repairing speakers. The resultant gaps were then filled with black silicone sealant. The end result is what you see below, it’s dirty, noisy and great fun to play through.

A few more sources of useful information

Run off Groove – The original Little Gem

LM386 DataSheet

Once I had the basic framework ready to assemble, a quick trip to B&Q sorted me out with the two tops. One for the work surface and one for the shelf, with quite a bit left over. Still, I’m sure I’ll find a use for the left over parts.

The frame was quickly put together and I then realised my first error. I hadn’t worked out a cutting list for the side pieces. As a result I ended up with two pieces, neither of which were quite long enough to go along the entire back length. If you look closely in the picture you can see two blue additions that are used to anchor the back panel.

It was a straightforward job to then cut out two notches in the bottom shelf. They’re even almost square and the shelf was screwed in place. Then the next hiccough. I hadn’t checked the cuts in B&Q as I’d misplaced my tape measure, so the top had been cut 10cm too long. Now I am no up to cutting a straight line the full width of the board so I needed a plan B. Checking it in place revealed that the longer top would still fit between the two cupboard doors and I would just need to alter it slightly to make it fit. So two more corners were cut out and I now have a slightly larger work surface which is a definite bonus.

One more hiccough to overcome which came to light as I pushed the now completed bench back into place. I’d failed to take into account the skirting boards which were now catching on the lower panels. Quick fix and the whole thing is supported on two pieces that were going to act as end pieces for the shelf.

Now it’s finished

I went out wandering today to get the other bits I needed as I don’t appear to have a tape measure anymore and I wanted to check that things were square, so a tri-square was in order. A couple of quid at the local dodgy hardware and pound shops has me fully prepared to bodge this together.

The first thing that has come out of this is that I now want a powered mitre saw even more than before. I’m getting a lot better at wielding a saw but I could have done in 15 minutes what has just taken me two hours and been a little more accurate about it.

I now have the basic frame which actually lines up square. I’m beginning to wish I had some large clamps so I could glue up the end pieces before I have to assemble the rest. I’m going to have a go to see if I can do it accurately with a couple of ratchet straps.

Back to the saw horse…

I recently dug out my old IBM A30 which suffered an untimely death after a fall from a high stool. I’d previously started to dismantle it to investigate the problem but came across a knurled screw head. Lacking appropriate tools at the time the laptop went back in the bag. I’ve since had cause to want a portable computer that has some real I/O ports on it so back out comes the old ThinkPad.

The laptop was suffering from serious corruption in text mode and occasional graphics glitches. Stripping the box down to it’s bare minimum I was able to successfully boot the GnuStep live CD. However then trying to install Ubuntu again would lead to the laptop hanging with a few random pixels and then a blank screen. Suffice to say it wasn’t particularly happy and looking on Ebay for an estimate on the parts value I found another six A30s for sale with the exact same fault.

So now I’m on the lookout for an A30 or A31 with a cracked screen so I can hopefully get one working without too much expenditure. Failing that a T21 looks tempting and cheap. It seems a waste to discard the Ultrabay drives, especially as one is a DVD rewriter, so I’m hoping to get something that supports Ultrabay 2000 and Ultrabay Plus. The only differences I can see being that only one has the connections for an additional battery.

I’ll keep things posted as things progress

I have in my little workroom a nice work table, situated in front of the window, which is a wonderful place to while away the time wielding a soldering iron. Unfortunately, the wandering nature of my brain means it isn’t really enough space to be able to just leave a project whilst I work on something else. And when the sun isn’t shining and I can’t get into the back garden, it’s a less than ideal spot to fire up the power tools.

On the other wall, against the chimney breast, there is currently a rather makeshift arrangement, with an old 19″ monitor (Yes I still have CRTs. Whilst I don’t use them much, and they take up far too much space, I really can’t bear to throw out such lovely monitors), an XBox and the stereo, perched on top of a plank on a keyboard stand – far from the best use of space. So I’ve been keeping one eye on ebay, and Freecycle for something I can use as a work bench. Nothing has appeared that really fits the bill, or more importantly, fits the extremely narrow space. As an aside, previous ideas have left me with a few piles of random timber in the under stair warehouse, so I’m casting off the fear of woodworking and attempting to build one myself.

As with all these things a quick google search and a flick through Make magazine showed that it may not be as difficult as I first thought. Certainly I have enough timber to build a sturdy frame, although possibly topless. I’ll go and buy a suitable worktop once I’ve shown sufficient motivation to build the carcass.

Continuing the Make theme I knocked up the following in Google Sketch Up, a program I’ve long since meant to get to grips with, and for which the workbench article in Make actual included a tutorial on designing the bench in the aforementioned app. So here is the grand design.

About as straightforward as it gets. Everything butt jointed and then glued and screwed. Tomorrow I’ll whip out the tenon saw and start challenging myself to cut right angles again.

As a postscript, although I’m very much a technology person it’s still very nice to start with paper and pencil…

Finally I sat down today to get on with drilling some of the enclosures to get the Big Muff clone and Purple Peaker painted and tested. Unfortunately in an almost typical act of stupidity I can no longer find the chuck key for my drill press. That’s two projects back on the shelf until I can get a new chuck key.