The three-way with a simple mechanical and electrical, making easy, no debugging, there is some practical value, it is suitable for amateur production.
Work

The electromechanical principle of Figure 1 ( Click here to download the schematic diagram ). It consists of a CMOS inverter composed of six. A-D composed of odd-level negative feedback amplifier. The feedback resistors R1, R2 and R1 adjust the ratio of adjustable voltage gain, the typical gain of up to 100 times. F3 and F4 in parallel to increase load capacity of the amplifier. E and F form a low frequency signal generator, it is a simple CMOS multivibrator. Its oscillation frequency is about 0.7Hz. Changes in C2, or R3, can change the oscillation frequency. R4 and MIC constitute pickup circuit.
In his hearing and memory intensive applications, the switch is placed in a position S, MIC will be converted to electrical signals into the external audio amplifier to amplify, and then by the headphone output. For memory enhancement, the use of dual headphones to listen to outside interference can be reduced.
For hypnosis in the device, the switch S 2 is placed in position, 0.7Hz low frequency signal is amplified by the transformer, the headset can hear "blah," the Beat sound, similar to the sound of rain, people relax, thus play the role of hypnosis.
Selection and production of components
Parts list below.