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1KHz Sinewave Generator: Build Your Own Oscillator
Simple circuitry, minimal distortion, battery-powered operation
A variable, low-impedance output up to 1V RMS is attainable
Circuit diagram
Components:
- R1 5.6K 1/4W Resistor
- R2 1.8K 1/4W Resistor
- R3, R4 15K 1/4W Resistors
- R5 500R 1/2W Trimmer Ceramic
- R6 330R 1/4W Resistor
- R7 470R Linear Potentiometer
- C1, C2 10nF 63V Polyester Capacitors
- C3 100µF 25V Electrolytic Capacitor
- C4 470nF 63V Polyester Capacitor
- Q1, Q2 BC238 25V 100mA NPN Transistors
- LP1 12V 40mA Lamp (See Notes)
- J1 Phono Chassis Socket
- SW1 SPST Slider Switch
- B1 9V PP3
- Clip for 9V PP3 Battery
Circuit description:
This circuit produces a respectable 1KHz sine wave utilizing the inverted Wien bridge configuration (C1-R3 & C2-R4). It possesses a variable output, reduced distortion, and low output impedance, enabling good overload characteristics. A small filament lamp assists in maintaining a stable long-term output amplitude waveform. It is useful for testing the Audio Millivoltmeter, Audio Power Meter, and other audio circuits presented on this website.
BC238 Transistor
The BC238 is a general-purpose NPN transistor known for its good switching and amplification characteristics. It is a common choice for a variety of low-power electronic circuits. Its 25V, 100mA current rating makes it suitable for this application. This transistor is frequently selected for applications demanding both switching and amplification capabilities, and it is well-suited to this circuit's requirements. The BC238 offers reasonable performance and is a widely-available component, rendering it a pragmatic choice for this particular design.
Notes:
- The lamp must be a low current type (12V 40-50mA or 6V 50mA) to ensure stable, low-distortion operation.
- Distortion at 1V RMS output is 0.15% with a 12V 40mA lamp, increasing to 0.5% with a 12V 100mA one.
- Using a lamp differing from the specified values may necessitate a modification of R6 to 220 or 150 Ohms to maintain proper circuit oscillation.
- Set R5 to read 1V RMS on an Audio Millivoltmeter connected to the output with R7 fully clockwise, or to observe a sine wave of 2.828V Peak-to-Peak on the oscilloscope.
- With C1, C2 = 100nF, the frequency generated is 100Hz, while with C1, C2 = 1nF, the frequency is 10KHz, and R5 needs adjustment.
- Higher gain transistors are preferred for enhanced performance.
circuit from http://www.redcircuits.com/