Published:2009-7-14 1:31:00 Author:May | From:SeekIC
The circuit design shown produces a Dr Who Dalek voice effect by chopping an audio signal at a low frequency. The best frequency seems to be around 50 to 90 Hz, and this is generated by IC1, a 555 timer. The arrangement shown is not an ordinary 555 astable multivibrator, but a hysteresis oscillator, which frees the 555 internal discharge transistor (pin 7) to act as a chopper, shunting the signal to 0 V internally. The chopped frequency is set by VR1, which is adjusted to give the most realistic sound. The input signal should be in the region of 50 to 150 mV rms from a low-impedance source-e.g., possibly a dynamic microphone-to avoid clipping the signal. The diode D1 is optional, and prevents the signal from losing symmetry, if overdriven. The output signal is fed to an external amplifier. The two dc-blocking capacitors C1 and C2 are optional and are needed only if any dc bias is present on the input signal side.
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