This is a simple three transistor frequency doubler circuit to raise an audio frequency by a factor of two i.e., one octave.
O1 is connected as a phase splitter with anti-phase signals·’ appearing at its collector and emitter. These signals are fed to two emitter followers Q2 and O3, which have a common emitter resistor, and thus add the two anti-phase signals. A degree of distortion is inevitable as shown in Fig. 2, but is acceptable for speech and soloists and produces a sound similar to the Chipmunks or Pinky and Perky.
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O1 is connected as a phase splitter with anti-phase signals·’ appearing at its collector and emitter. These signals are fed to two emitter followers Q2 and O3, which have a common emitter resistor, and thus add the two anti-phase signals. A degree of distortion is inevitable as shown in Fig. 2, but is acceptable for speech and soloists and produces a sound similar to the Chipmunks or Pinky and Perky.
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