My Theremax project

Previous posts on other thereads:

9/11/2007 1:03:40 AM - edit
Well, I got the pitch antennae made, using 3/8 inch 0.035 in wall aluminum tubing like I used for the volume antenna. I made two lengths, 18 inches and 24 inches in height, with a 90 degree bend at the bottom to work with the connectors I have. I had hoped that I could make the 90 degree bend with a jig, like I did with the volume antenna (which has bends of 10.75 and 6.0 inches in diameter). I tried for a 2-in. diameter bend, but no matter how careful I was, I couldn't do it--the tubing flattened. I bought a proper (albeit designed for softer copper tubing) tubing bender at the hardware store, and by calling on my inner gorilla I was able to make good 90-degree bends (one inch diameter) in the aluminum tubing. So now it is on to the case/box for my Theremax. It will be somewhere between a Kees and an Etherwave--red oak, 18 inches wide, 7.75 in. deep and 6 in. high (457 X 19.7 X 15.2 cm).
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9/14/2007 11:22:24 AM - edit
Here's a picture of the jig and antennae I made:

http://www.abarbour.net/antenna.html

The base is a scrap pine board; the shaped pieces are made from some scrap particle board, roughly shaped with the jigsaw, shapes finished with the rasp, and the edges grooved with the round file. The small round piece was intended to make a 90-degree bend in the pitch antenna, but that didn't work. I could still use it to finish bending the volume antenna. (Of course it sprung open a bit after being shaped on the large circular gizmos.)
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9/15/2007 12:01:07 AM - edit
Here are the connectors for the antennae:

Swagelok bulkhead union, brass, 3/8 inch:
http://www.swagelok.com/search/product_detail.aspx?part=B-600-61

I am familiar with this product from work, and had the boss order me a package (four). The invoice hasn't come in yet, so I don't know the price. Note that on each end there is a nut. Inside each nut is a pair of ferrules, front (cone shaped) and back (a 2-level ring). Slip the nut onto the end of the tubing, followed by the back and then the front ferrule. Put the tubing into the fitting as far as it will go, then tighten the nut as far as it will go, not just to where you feel resistance. Back the nut off, and the ferrules are connected so firmly to the tubint (a little back from the end) that the only way to remove them is with a hacksaw. The only washers I found at the hardware store that would fit these unions are so big I think I will skip them on the outside, since the case will be red oak and pretty hard. On the inside I will put a washer and lock washer, and maybe a spade lug underneath the lock washer will make a good electrical connection.

They also sell straight copper tubing that I think might very well work; it's the same size as the aluminum tubing I used. In October I will pass by a Swagelok distributor, and I might take a look and/or buy a length.

Swagelok copper tubing (note 3/8 inch, 0.035 in wall, 10 ft straight):
http://www.swagelok.com/downloads/
webcatalogs/EN/MS-01-160-SCS.PDF

Dealers:
http://www.swagelok.com/distributors/
locate_dist.aspx

Discoveries about copper-clad printed circuit board:

1) It is a good shielding material.
2) It is a good structural material--very stiff.
3) It is easily cut with either tin-snips or (if sandwiched between pieces of wood) a skil saw.
4) If the hole you drill in it is a bit small, it can easily be reamed out with the tang of a file.

I succeeded in winding a pair of air coils for my Theremax pitch anteena today. Two--because that's what fits easily--air coils in series with taps at 0, 100, 200, 300, 450 and 600 turns, selectable with a rotary switch.

Here are the instructions I used for inspiration::

http://www.oldtemecula.com/theremin/ultimate2b/
newcoil.htm
and
http://www.oldtemecula.com/theremin/ultimate2b/
boxwinder.htm

I used two 2-inch PVC couplings spliced together for each coil. 300 turns of 30-gauge enameled wire fit on with just enough room left for a clamp on one end and a bit to spare on the other. (The 30-gauge wire from Radio Shack comes on a 200-foot roll with a couple of other sizes in the same package. I figure each coil uses about 120 feet, so I needed two rolls.) Not surprisingly, the second coil looked better than the first. I learned to put some Scotch tape around the joint in the middle, for one thing. I improved on the winding device linked above by using PVC sprinkler parts I had on hand to make a crank. When I started I had to tamp the coils down every two or three turns; by the end I could go ten turns before tamping them down. I didn't put metal cores into the coils, but can do so if I should so desire.

I had to actually wind the coils and get them in place so I can drill various bolt holes in the bottom of the case before I proceed to the sides of the case, otherwise it would be the Devil's own work to assemble. Now I can proceed to the front, back, sides and top. Photos made and will ensue in due course.

MY RESEARCH PROJECT, after I get the T-Max built, will be to test the linearity at various coil settings and two different pitch antenna sizes. A friend with an oscilloscope will help, and I will post the results here once I have them. Of course no two types of theremins will have just the same quantitative response to such tinkering, but the qualitative responses should be similar, and therefore it should be of general interest, I think. The electronics experts have probably figured it all out long ago, but I don't have their knowledge, so I must resort to empirical tinkering.

A couple more notes on making the coils: I secured the coupling to the axle with duct tape, and finished by pinning things down with a bit of hot glue. I had no need to solder the twists on the taps.

Working on the case today, and it is starting to look like a case. I am far from being a professional cabinetmaker, and it shows--but most of the "artistic" touches will be covered up or invisible from a few feet away.

Alan

I'm very interested in your coil. Could you post some pictures when your done?

I think i'll be doing the same thing for my theremax. At the moment all the electronics are done. Seeing as i'm making a very different case to what the theremax is normally housed in, i've had to do allot or rewiring and such. (i'll post pics when i'm done). When i have some information on my coil project for the theremax i'll give you a yell.

Keep up the good work!

Tim

I certainly will post pictures--last night I cleared out a bunch of files on my server to make room for a theremin project web page with photos: antennae, coils, case, assembled Theremax, and pitch linearity graph. I have no idea if the coils I am splicing in will truly be helpful, but I will find out. I have roughly figured out how to test the pitch linearity--it will be a two-person job; me to produce the tones, and another to read the distance from my hand to the pitch antenna from an indicator I will build and record the frequency from an oscilloscope. I am building my T-Max into a box with roughly the footprint of an Ethermax, although higher to accomodate the T-Max control panel. That left me an area of about four by six inches for the coils.

Theremax project web page, with photos:

http://www.abarbour.net/tmax.html

I need some small (50 ohm) coax, RG174U. Can't find any around here, can't find a small amount for a reasonable price online. Anybody have some to spare? Say 3 or 4 feet?

The folks at PAiA are sending me the extra coax. Just like others have said, their customer service is first-rate.