The RS Illusion Theremin

Update 08/15/08

The New RS Illusion Theremin
A Modified Ult-2c
100% Radio Shack

My theremin board uses "Illumination" Volume Control,
with focus on the true theremin sound.

RS Illusion PDF (461k) Revised 08.08.08

Iron it on!

Construction Order Below:	6. The Lev Antenna for perfect linear pitch
1. RS Illusion Parts List Updated 08.08.08	7. Diagnosing The Sound of Illusion New 7.11.08
2. Etching your own PC Board It's really not difficult!	8. VAPP Optical Volume Control or use a simple LDR photo resistor
3. Assemble your Board FAQ Look this over!	Panel Mounted Controls
4. Making the L2 Coil	The Modified Ult-2c Photo of Modifications
5. Tuning the Oscillator	Photos & Notes from my backyard!
Email - Christopher: "Tell me what major city you live near." theremin@oldtemeculaX.com <=Remove X from your Email Address Box.

The toner laser printer RS Illusion PDF (461k) theremin iron-on is here! Revised 08.08.08

Note: Orientation of the L2 coil is critical. The metal side plate must face the LED 2 side of the board.

Mount the two 100uh "L1 choke coils" with 3/4" clearance above the circuit board.
The two choke coils L1-A & L2 - B must mount in the same direction

The Modified Ult-2c has evolve into the new RS Illusion board:

R8 - Located on the board below U4 but not on the schematic is for the Ultermen Output (not used)

You could substitute R8 with a 4.7uf non-polarized capacitor and use this output as a
pitch-preview with an earpiece that has an inline volume control.

C13 - .1uf is not shown on the schematic but has pads on the pc board. This is only
used if you separated the RT pads to use the remote null adjuster. (not used)

C20 - 4.7uf capacitor (Audio Out) is Non Polarized. Mount it standing on end, either side up.

RT (R-Tune) is on the lower left side of the board, is a resistor method of tuning using a low ohm pot (25 ohms?). You could run wires to remotely adjust your Null point several feet from the theremin. I have only tried this on my bench setup. The white line indicates the pads are normally connected together when RT is not used. This is already connected on the copper clad side of the board so "do not drill" the pads apart!

The TLC555 adds distortion to keep the theremin tone from sounding like a slide whistle.
It is also a simple way to drive the LED 1 with a good square wave which visually
indicates the NULL point or zero beat.

How to add a Pitch Preview to the RS Illusion or Build the new VAPP board.

Use the Output terminal + pad to the left side of LED 1 and replace the R8 -100 ohm resistor with a 4.7 uf non-polarized electrolytic capacitor. Use headphones that have an inline volume control on the cord. This wire connection should be through the tip connection on a three wire stereo jack; while the normal Audio Out to the CdS volume sensor is from the middle plug connection. Wire your headphone jack at the remote volume stand where the CdS sensor is located to keep the headphone wire from interfering with the pitch electro-magnetic field. This also allows for the shorter headphone cable.

The RS Illusion theremin works best using the CdS volume control fed into the sensitivity of a microphone level input or a guitar amplifier. Keyboard amplifiers are not as sensitive and will probably sound quiet unless using the new VAPP illumination volume control board.

The new VAPP volume control board will greatly enhance the use of the CdS volume control method.

RS Illusion board current is < 10 ma. A 6 volt Lantern Battery would last the rest of your natural life!

I developed my best theremin sound using 6 volts rather than 9 volts, plus the battery lasts longer.

The purpose of the two diodes on the TLC555 pins 1 & 8 are my kludge method of narrowing the trigger window.
Pins 5 & 7 of the TLC555 are not connected to anything.

The theremin needs a good "earth ground" to work properly. This is most often achieved through the audio ground and the three prong power connection of your amplifier. Amplifiers using a wall wart adapter or two prong plugs "will not" work properly, in this case get a direct earth ground connection from somewhere else.