Constructing a Jaycar: Tom's adventure in electronicland

Posted: 1/16/2007 6:05:51 PM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

This weekend I started work on my Jaycar (mk 1) Theremin kit.

I haven't assembled an electronics kit for 20 years, although way back when I was taught how by my father, who was an electronics technician once upon a time. I was surprised how much came back to me, actually. But, I took the precaution of starting on the kit while visiting my friend Gene, who is an electronics technician and repairman for a living, and had kindly agreed to be my advisor on the project.

Some initial impressions:
* The manual comes with a guide to identifying the various parts that are included with the kit. Not all the parts are shown. Some parts I had to ask Gene about, some I had to guess at. ("This must be the part that goes in that spot, it's the only thing that's the right shape...") One part just seemed to make no sense, we eventually guessed it must be the jack for the external power supply.

* The resistors are, as normal, labeled with color bands, and the manual provides a handy chart to look up the pattern of colors. It fails to tell you in which order the colors are read, although that's not a big deal because I don't think they work in reverse. Also, a problem I've always had with resistors is staring at them and wondering "is that red, orange, or brown?" Ultimately I did the obvious ones first ("hmm, it says there are six of this kind with brown black black black brown, and there are only six of one kind and it looks like brown black black black brown, so that must be it...") and then figured out the rest by process of elimination.

* I *tried* to use a 15w soldering iron, but really, the solder needed 30w.

* The solder really likes to follow the circuit traces on that board. Despite careful soldering, and despite that Gene says I actually did a pretty good job, this created a lot of spots that looked like solder bridges, but aren't really. I had to keep referring to the picture of the board in the manual to make sure that spots that looked like a solder bridge were actually okay.

* They don't explain well how to read the circuit board to figure out what part goes where, and I think a few of their markings may not have been entirely standard for U.S. norms. Some guessing was involved, even with Gene's professional help, although it wasn't too bad.

* The capacitors had another lookup table, by which you could look up what was written on the capacitor in one column (it didn't say which, and it would only match part of the very long numbers written on some of the capacitors) and then something in one of the other columns (it didn't say which) would be what was printed on the circuit board. This was helpful, but insufficiently obvious.

All in all, I think the kit is a very nice and relatively easy kit for anyone who has any experience assembling circuit boards and is willing to take a few tiny leaps of faith, but would be very bewildering for a beginner on their own.

So, on that first evening of work I soldered all the parts onto the board. I haven't made any attempt to install it in its case yet. Next time I visit Gene I'm going to rather loosely install it in its case, just for testing purposes, and then as soon as it's working I'm going to sit down with Gene and we're going to discuss modding the board and making a much nicer wood case for it.

In an unrelated note, some months ago I bought a (used) Moog Concertmate MG-1 ( synth on ebay, broken. The seller was blunt that it didn't turn on. It consequently was selling for about 1/4 what similar units were selling for in working order and poor cosmetic condition. I figured, "doesn't turn on" is probably either really bad or really trivial, and I'd take a bet on it. So, I dropped that off with Gene while I was visiting him about the Jaycar. Good news: he called me on monday to tell me he'd opened the synth, and that inside it's in pristine condition, all original equipment, e
Posted: 1/28/2007 7:26:12 AM

From: sunnyvale california

Joined: 1/28/2007

That does not surprise me, I've bought such things as a McIntosh amp in really nice condition for ..... wait for it.... 5 bucks! Because the fuse cap (and fuse) were missing. I went and got a new fuse holder, installed that, installed fuse, interestingly all that cost me $7.50, more than the amp cost! Then took it out to the TRW swapmeet and sold it for $250, and the guy who bought it knew I had it in my trunk before he could see it, unless he had x-ray eyes and could see through me. Weird! Other stuff, stuff gets dropped and large componants like transformers and large electrolytic caps come loose, or cable connections come loose.... stuff like that.

Fuses sometimes just get tired. And blow. A little power surge helps.

Here's a tip: When buying electronics used, sniff! If you smell a burned smell, proceed with caution.
Posted: 2/19/2007 4:13:32 AM

From: Undisclosed location without Dick Cheney

Joined: 2/21/2005

Sunday evening I went for round two of construction. This time, I didn't get a lot done, but I didn't spend a lot of time either.

Having installed all components onto the circuit board itself last time, what's left is the antennas, speaker, knob, and sockets. I have already decided that I will only be using the included antennas to test the board and will be replacing them with better antennas later. Also, I will be replacing the little plastic box with a nicer and larger wood cabinet. (I'm thinking the same size and shape as an etherwave standard.) So, it makes little sense for me to carefully install the board into the included box and permanently attach the antennas.

Consequently, I installed the two antennas into the plastic box, and while at it I attached some wires running from their leads to outside the box through one of its holes. I'll attach them to the board when I'm ready to test it, then I'll remove them after it's tested good, in preparation for the new antennas and mods.

I also attached some longish wires to the speaker, but didn't connect it to the board. I'll do that when it's ready for testing as well.

I did wire up the knob to the board, but I gave it longer wires than called for, so I'll have more freedom in placing it in whatever case I end up making later.

I ended up leaving it at that for the night: it now requires a power supply, which I haven't purchased, and a new socket with which to connect the power supply, because the one included with it doesn't look like it will fit American power supplies' connectors. I'll be getting together with my project advisor to select and purchase that stuff sometime soon. After that I'll do a complete temporary assembly of all the parts, calibrate and test it, and if it's all good I'll then disconnect the antennas in prep for mods.

I have lined up a welder who is interested in making one set of antennas for me for this instrument out of stainless steel. For my other kit, the MIDI theremin, I'll probably have a set made out of anodized titanium by my jeweler. (She specializes in science fiction jewelry and will likely do something creative with the volume antenna for me.) I need to communicate with both further to refine some specs for the new antennas so that I can have both sets made to be about the same; I may also look up what info I have on the RCA antennas and see if that might provide useful sizes. Ideally I hope to end up coming out of this with two vendors who are enabled to make Theremin antennas to order according to my specs (or Lev's, if the RCA antennas end up being the choice), which will be published with the relevant information to integrate them into the projects. I think this would be good for the Theremin community (a new source for parts!) and good for my friend the welder and my jeweler (more work!).

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