Variable Wien Bridge Oscillator

7 A Wien bridge oscillator can be made variable by using two frequency determining parts that are varied simultaneously at high tracking accuracy. High- quality tracking potentiometers or variable capacitors are, how- ever, expensive and difficult to obtain. To avoid having to use such a component, this oscil- lator was designed to operate with a single potentiometer. The output frequency, 1"0, is calculated from fo=1/(arrlIC/a) where R =R2 =R3 =R4 =Rs, C=C, =C2, and a = (1)1+16)R. Preset P2 allows adjusting the overall amplification such that the output signal has a reason- ably stable amplitude (3.5 Vpp max.) over the entire frequency range. The stated components allow the frequency to be adjusted between 350 Hz and 3.5 kHz. Other frequency ranges are readily defined with the aid of the above formula, although it should be noted that the upper Parts list Resistors ± 5%): R, =10K R2;R3;R4;136=100K R5 2M2 P I IM O linear potentiometer P2 -- 5k0 preset Capacitors: Cit;C2 =1 n5 C3;...