This is a design circuit for generates a good 1 KHz sine wave adopting the inverted Wien bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. The figure is shown in below.
The bulb must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term stability and low distortion. Distortion @ 1V RMS output is 0.15% using a 12V 40mA bulb, raising to 0.5% with a 12V 100mA one. Using a bulb differing from specifications may require a change of R6 value to 220 or 150 Ohms to ensure proper circuit's oscillation. Set R5 to read 1V RMS on an Audio mili voltmeter connected to the output with R7 rotated fully clockwise, or to view a sine wave of 2.828V Peak-to-Peak amplitude on the oscilloscope. With C1, C2 = 100nF the frequency generated is 100Hz and with C1, C2 = 1nF frequency is 10 KHz but R5 requires adjustment. High gain transistors are preferred for better performance.
Component Part:
R1 5K6
R2 1K8
R3, R4 15K
R5 500R 1/2W Trimmer Cermet
R6 330R 1/4W Resistor
R7 470R Potentiometer
C1, C2 10nF/63V
C3 100µF/25V
C4 470nF/63V
Q1, Q2 BC238 25V 100mA NPN Transistors
LP1 12V 40mA Filament Lamp Bulb (See Notes)
J1 Phone chassis Socket
SW1 SPST Slider Switch
B1 9V PP3
Clip for 9V PP3 Battery
The bulb must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term stability and low distortion. Distortion @ 1V RMS output is 0.15% using a 12V 40mA bulb, raising to 0.5% with a 12V 100mA one. Using a bulb differing from specifications may require a change of R6 value to 220 or 150 Ohms to ensure proper circuit's oscillation. Set R5 to read 1V RMS on an Audio mili voltmeter connected to the output with R7 rotated fully clockwise, or to view a sine wave of 2.828V Peak-to-Peak amplitude on the oscilloscope. With C1, C2 = 100nF the frequency generated is 100Hz and with C1, C2 = 1nF frequency is 10 KHz but R5 requires adjustment. High gain transistors are preferred for better performance.
Component Part:
R1 5K6
R2 1K8
R3, R4 15K
R5 500R 1/2W Trimmer Cermet
R6 330R 1/4W Resistor
R7 470R Potentiometer
C1, C2 10nF/63V
C3 100µF/25V
C4 470nF/63V
Q1, Q2 BC238 25V 100mA NPN Transistors
LP1 12V 40mA Filament Lamp Bulb (See Notes)
J1 Phone chassis Socket
SW1 SPST Slider Switch
B1 9V PP3
Clip for 9V PP3 Battery
