This circuit generates a good 1KHz 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. A small filament bulb ensures a stable long term output amplitude waveform. Useful to test the Precision Audio Millivoltmeter, Three-Level Audio Power Indicator and other audio circuits posted to this website.
Parts:
R1____________5K6 1/4W Resistor R2____________1K8 1/4W Resistor R3,R4________15K 1/4W Resistors R5__________500R 1/2W Trimmer Cermet 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 Filament Lamp Bulb (See Notes) J1__________Phono chassis Socket SW1__________SPST Slider Switch B1_____________9V PP3 Clip for 9V PP3 Battery
Notes:
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 Millivoltmeter connected to the output with R7 rotated fully clockwise, or to view a sinewave 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 10KHz but R5 requires adjustment.
High gain transistors are preferred for better performance.
Read more:http://www.redcircuits.com/Page13.htm
