Advice, please, on modifications

Posted: 8/10/2007 1:47:09 AM

From: Fresno, California USA

Joined: 3/26/2006

Hi! I was recently inspired by the movie "Theremin: an Electronic Odyssey." I could use a hobby (I'm on the wrong side of sixty), and it seems to me that if I were to build a theremin I would probably be sufficiently invested in the project to keep at it and really learn to play. Buying a ready-made theremin would not offer that degree of psychologica investment up front.

I figure the PAiA Theremax looks pretty good, but there are also a number of modifications here and there that seem promising; if they really work, why not add them in the first place? I would be very grateful for any advice from those who have installed the following Theremax modifications:

From the PAiA modifications page(s):

if you connect a 10k ohm resistor (brown-black-orange) to these same circuit locations, instead of the "gimmick", the resulting change in sound is spectacular ...

You can remove the .005uF ceramic disk capacitor C44, which is connected between the collectors of Q10 and Q11. Simply clip it's leads off flush with the circuit board. This will make the square wave timbre very reedy.

To set it up so I can hear the theremin without disturbing others:
9605K Headphone Buffer Amp Kit

From Fred Nachbauer's web page:

"Timbre Control Modification:
Replace R40 with a lower value (I used 150K). This gives a smoother, more even transition between sine and square wave sounds...[Replace] R81 (the 100K Timbre pot) with a log-taper (audio taper or "A" type) pot of the same value as the original"

"Birdies can be reduced considerably by lowering the frequency of the pole of the low-pass filter after the mixer to about 34 kHz. (from 156 kHz.) by increasing the value of C22 and C34 from 220 pF to 1000 pF."

"Shielding the "reference" oscillators with small pieces of un-etched pc board (on both sides of the Theremax board) greatly reduces the tendency to lock up near zero-beat. Without the shielding, lockup occurs at around 20-30 Hz. With it, you can get stable frequencies down to under 10 Hz."

Of course replacing the PAiA antennae with more substantial ones, probably made to the model of the RCA antennae using the plan and jig shown here at Theremin world.

I wonder about adding a mute pedal; maybe later on. The ones I have seen seem a little expensive.

Also an induction coil in line with the pitch antenna--is bigger better and still bigger better yet?

For a practice speaker/amp, the Moog theremin amp looks OK, and is not overly expensive.

Thanks in advance to all.

Alan in Calfornia
Posted: 8/10/2007 6:17:11 PM

From: Fresno, California USA

Joined: 3/26/2006

I just located a good type of connector for antennae at

3/8 inch bulkhead union
comes with two nuts, two sets of front and back ferrules.

They also sell 3/8 inch tubing, but I am not sure how soft it is.

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