RS Illusion - Illumination Volume Control

This could also work good with other theremins that are pitch only.

As your hand lowers to cover or shadow the photocell, the volume quiets. The resistance will increase to several mega-ohms. Greater than a 12" window of control from Full Volume to Total Cut Off is possible. This transition creates a clean low volume range. A crystal ball creates one of the better methods to focus the incoming light from above that I have found.

Currently I am designing a small volume control circuit board so the CdS sensor will have output pre-amplification to drive the input of any amplifier from mic level to line level. Also the Pitch Preview will be taken from this circuit board with a panel mounted volume control. On the RS Illusion circuit board the big square pads at R10 are where the battery power will come from. This would be one of the three connections using a stereo jack, the other two connections would be the Audio Out and Ground.

Features: This is the simplest and most natural volume control design!

Setup properly in the controlled environment of your own room this method of volume control can surpass the control of the RCA hoop style antenna using the same arm motion.

This CdS volume control method outputs a clean & undistorted signal (sound).

This illumination setup works excellent with a white ceiling in normal bright room lighting.

Wide "fade out range" with excellent undistorted control on the quiet side or complete on or off.

The input of this volume method works best driving it at Line level then fed into a microphone or guitar amplifier. If you need more volume from your Amplifier use 9 volts with your RS Illusion instead of 6 volts to increase the RS Illusion signal level output.

Use shielded audio cable on the out side of the CdS to your main amplifier to avoid 50/60 hz hum.

Your theremin will get an adequate ground if connected to any amplifier with a three prong plug.

Home Depot has a package of two for $5

R1 - CDS Photocell - remove it from any bathroom plug in nightlight, they worked the best.

I have tried the Radio Shack 5 pack of CdS cells 276-1657 they are not effective. They did not have a wide Light to Dark response resistance.

The photocell should be mounted on its own enclosure which can allow for better volume response.

Having the volume control separate from the pitch control base allows for better placement of the two controls. Sometimes you may want a left handed volume or a setup closer to you when you're playing the lower outside octaves.

Black out the sides (try black tape) and use the plastic cover over the top of your CdS cell. This directs the light from above to your CdS cell mounted below it.

I will have a better example of this soon.

Halogen lamp light works better than incandescent bulbs to minimize any 50/60 hz hum. Bouncing bright light off a low white ceiling is ideal. Battery powered super bright LED lamps also work good.

Note: The lower half of the crystal ball could be painted black to block bottom light.