Low Frequency Wien Bridge Oscillator

 Low Frequency Wien Bridge Oscillator

Circuit Project Description

The circuit was created to produce an oscillator operating at low frequency for use in the production of electronic music and experimenting and testing tone controls.

TerminologyOscillator – an electronic circuit that produces a time varying or repetitive electronic signal, sine wave or square wave, without an external input signal using positive feedbackTone Control – an electronic circuit used to modify an audio signal before it is provided to headphones, speakers, or recording devices by the use of amplifiersWien Bridge Oscillator – a type of electronic oscillator that uses an RC high pass filter and an RC low pass filter for setting the frequency of oscillation while generating sine waves without any input sourceBC549B – a bipolar NPN Epitaxial Silicon transistor designed for general purpose and switching applications due to its high voltage and low noise characteristics  Circuit Explanation

By definition, the frequency of a low frequency oscillator is low. The signals being produced can be as low as 0.01 Hz while the upper frequency can be as high as 20 Hz limit. This circuit will impose an audio technique that will create a pulsating rhythm instead of an audible tone. Using a single bipolar transistor, the circuit is structured like a regular Wien Bridge Oscillator which consists of four resistors and two capacitors. The combination of resistors and capacitors will provide feedback to cause the circuit to oscillate. This type of RC oscillator circuit prevents distortion of the output signal and regulates the amplitude of the generated signal. The frequency of the generated signal is modified by altering the values of the timing components consisting of resistors R1 and R2 and capacitors C1 and C3.

The regenerative feedback is applied through capacitor C2 upon rendering power to the circuit. The feedback travels from the collector to the base of the bipolar transistor. To begin the oscillation, the preset variable resistor or potentiometer RV1 is adjusted. The oscillation of full amplitude would reach up to 4.8 seconds, given the values in the diagram. Having to build this circuit would result to controlling the amount of generation and regeneration by proving low frequency oscillation and thus causing a low harmonic content of the developed signal, having a way of tuning over a wide scope of frequencies without having a change on the amplitude of the signal, for fast switching of developed signal frequency, and avoiding excessive harmonic content to the signals during frequency switching.


A low frequency oscillator finds its way in modulating other factors of an audio and not for the purpose of being a sound source as compared with standard oscillators. They can be directed to provide control in the amplification, filter frequency, stereo panning, and the frequency of the oscillator. It can produce various effects in sound synthesis and sampling by producing regularly repeating waveforms such as square, sawtooth, triangle and sine, at a very low pitch or frequency. As an audio oscillator, the modulation of the pitch would produce a vibrato, the modulation of volume or amplitude would result to a tremolo and the modulation of filter cutoff would result to wah style effect. The parameters being controlled by this type of oscillator in most synthesizers include a rate control, routing options, waveform varieties, a tempo sync feature, and the amount of audio signal that will be modulated.

In more complex applications, they may be used to control the rate of arpeggiation or triggering gate envelopes whereas, it can provide a melody with simple tremolo or vibrato in the field of electronic music. In modern music, it is used to provide a number of sound effects like a bass sound for low rate and a rippling sound for high rate.

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