The setup of Theremin is very easy. Speakers of required range is connected to one end, an extension cord for power supply, adapter and connectors. It is a very simple setup.
How does it work?
Theremin is an electromagnetic device which produces sounds with varying electric field. It has a resonance circuit which has two radio frequency oscillators. Among the two oscillators one is the beat frequency oscillator operating at 285 kHz and the other is the ring modulator operating at 282 and 285 kHz. It also consists of variable oscillator which depends on Capacitance.
There are two antennas in both the ends in which one of it is used to vary the pitch whereas the other one is used for volume variations. The pitch antenna consists of variable oscillator. The pitch is varied with the help of hand movements. As we move our hand near to the antenna the capacitance increases and frequency lowers, similarly when we move our hand away from the antenna there is reduced capacitance and increased frequency.
The two oscillator outputs are given to a mixing circuit. In the mixing circuit the two signals are superposed. These superposed signals produce a beats having frequency which is equal to the difference of the input signal frequencies. As the variable oscillator frequency is lowered the beat frequency increases and if oscillator frequency is increased the beat frequency reduces. The beat frequency lies between 65 Hz to 3 kHz. These mixing signals are not strong enough to be transmitted. So the signal frequencies extracted by the mixing circuit is sent to voltage controlled amplifier. The second antenna is the volume control antenna. The volume control antenna consists of a LC circuit connected to 450 KHz oscillator. It works on principle of resonance. As you move your hand away from antenna the voltage across the inductor circuit increases.
The amplification of the output of volume circuit is done by filament in the vacuum tube. For heating the filament in the vacuum tube current from volume oscillator is provided to it. So when player brings his hand near the volume antenna the resonance of the oscillator is withdrawn which leads to drop in filament current thus reducing gain of amplifier and leading to reduced volume.