My Theremax project

Thanks, Gordon. It might be quite some time before noise removal would fail to remove all the sounds I make on a theremin...

I started assembling the circuit board this evening. Got all the resistors, a couple of capacitors (I almost dated myself by writing "condensers") necessary to route a resistor for a modification, and the oscillator coils. Don't know what I'd do without a handy magnifying glass on a stand I picked up at Radio Shack. On to condens...er, capacitors tomorrow evening if I get off work at a civilized time.

I got all the condensers installed last night; tonight perhaps diodes, IC's and transistors.

Last night I got all the diodes, transistors and integrated circuits onto the board. I addition to the magnifying glass on a stand [http://www.radioshack.com/product/index.jsp?productId=2104639&cp=&parentPage=search] (you can toss all the other stuff that comes with it) I found a strong hand lens was REALLY great for checking my work for solder bridges etc. The Radio Shack 15/30 watt soldering iron is fine (15 watts is plenty). Soldering braid worked well to unsolder items. If doing it again, I would install the diodes either first or after the resistors, so I could put a heat sink on each one. Done after the capacitors, I could only use it on about half of them.

I spent quite some time figuring out how to install the pitch antenna coils. From the beginning I had planned to mount them horizontally, side by side, with a connector strip between, and I will continue with that setup because all the pieces are cut and the holes drilled--but if I were doing it again, I would probably mount them vertically (which would require longer taps), because that would give me a lot more room to work. This way the clearances are *awfully* small. I think I will have to connect everything (coils, connector strip, rotary switch, grounding wire) before mounting the whole bunch together. It would be much nicer to install one part at a time and then the wires.

The camera tripod mount I devised seems to have worked out well. A mic stand with a mounting flange would be easier, but I had a good tripod and didn't find a sturdy and stable mic stand. (Not that I looked very hard.)

Photos should ensue within the week.

I made a lot of progress today; panel wired, PCB almost all soldered--but I haven't connected the two. I will hold off until the 6800 ohm resistor and the 100pF capacitors for C39 and C44 come in from PAiA for suggested modifications. It's all looking very impressive! I discovered the 15/30 W soldering iron I was using wasn't powerful enough to handle three wires going into a lug on a panel potentiometer or jack; but my old 100 W soldering gun worked just fine. I don't know what I would do without a strong hand lens. I decided to try running the fly wires *underneath* the PCB for the sake of appearance, rather than above--but quickly (like on the first wire) discovered that trying to solder wires going in from the bottom was a big mistake. It was too hard to avoid creating solder bridges. I will try to neaten up the wires some other way. I installed a power plug so I can disconnect the wall wart from the theremin--but realized that if I did that I would have to run some extra wire inside the case so I would be able to pull the PCB for troubleshooting etc.

Tomorrow I will go forward with wiring the supplementary pitch antenna coils.

I got the pitch antenna coils assembly built and installed, continuity and ground OK. I was afraid it was going to look pretty bad, but by the time I got it done (having corrected a couple of misadventures along the way) it actually looked passable. Waiting now on three condensers and a resistor coming from PAiA for further modifications before I complete the circuit board and connect the fly wires, which should be the last assembly step. Maybe one more evening's work.

On the basis of various suggestions I found here and there, I made some modifications to the Theremax. These fall into categories:

My own ideas:

1) Pitch antenna coils. A noble experiment, in progress.
2) Push button mute rather than jack and foot switch. Done.
3) Power supply plug. Done.
4) Longer case to get the antennae further apart, possibly giving addition flexibility in tuning. Done.

Widely recommended:

5) Antennae more like RCA ones. Done.

Suggestions from PAiA web site:

6) 10K ohm R from R4 to R9 (on side nearest to oscillator coils) to improve tone.
7) Delete C44 to improve timbre in square wave

Suggestions from Fred Nachbaur:

8) Extra shielding around oscillators--very difficult; not done.
9) Not explicitly stated, but photos indicate fly wires soldered to underside of board for better appearance. I tried it, and it calls for soldering skill greater than mine. Not done.
10) To decrease birdies, C22 and C34 220 pF-->1000pF
11) To improve timbre fader response, pot. R81 100K --> 100K log taper (audio taper) and R40 470K --> 150K.

HOWEVER, there are new mods suggested by PAiA [yes, they DO have outstanding customer service]. They currently suggest 100 pF capacitors for C39, C44, and C37, plus a 6.8K ohm resistor between R81-3 and R81-2 to deal with all the items addressed in mods nos. 6, 7, 10 and 11 above. I will remove the previous mods and follow the PAiA suggestions as soon as the parts arrive from PAiA. They say these new mods also improve some of the stuff (I'm kind of vague here) related to timbre effects of rapid attack and (I think) CV outputs related to same.

Got it all re-modified as per latest PAiA suggestions and very close to finished. (Would have loved to finish it last night, but had already stayed up much later than I should have.) Only three or four wires left to connect, then I can clear off my workbench. Screwing the front panel to the case (which I left until after I had the wires all soldered to it) took nearly an hour because of having to use a right-angled phillips screwdriver in very cramped quarters; I'm REALLY glad I had the foresight to drill pilot holes for the screws when I was making the parts for the case.

Hang in there guy. Us builders have to stick together.

PHILIP

Just saw your post about RG174. I may have had some. Next time you need radio / electronic stuff email me.

ka4koe@arrl.net

Philip