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Radio Frequency Mixer - Experimental use with audio.
This is the same as the mixer used in a superhet receiver but audio frequencies are being used instead.
This circuit has been tested. The goal was to produce Dalek like sound effects. It worked.
- The SA602AN chip multiplies the two input signals together.
- As this is a double balanced mixer, the output contains only the product. The input signals do not appear in the output.
- Quite large coupling and decoupling capacitors are needed because the audio frequencies are low and the inpit resistance of the chip is about 1.5 kΩ
It might be possible to use this as a voltage controlled volume control where the DC voltage on one input alters the gain of the other input. Automatic gain control might be possible too.
The SA602AN is available from Farnell for about £2.00
- The microphone drives a non inverting audio pre-amp with a gain of 67.7.
- The audio level into the SA602 mixer should be about 200 mV.
- The local oscillator signal between 20 and 50 Hz should also be at about 200 mV.
- There is a Zener diode providing a 5 Volt supply to the SA602 chip.
- Take care NOT to apply 12 Volts DC power to the mixer chip.
- The photo shows a "line" signal connected to the SA602, bypassing the microphone amplifier.
This could come from an iPod, phone, computer or any other line output device.
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