The filter circuit of this main circuit will sent to through to the signal that middle frequency. At the same time is attenuated the others frequency into input signal to R1 through the base of emitter circuit as complementary form (T1/T2). And the feedback from the emitter lead of T1 and T2 through twin-T to input of the complementary amplifier (T3/T4) at others frequency from feedback.
Then, out to the collector lead of T3 and T4. By there are the phase opposite the input signal. Thus, at a moderate frequency of the twin-T has been reduced significantly.
Therefore, The signal level at the middle frequency has a few only. Which will be sent out of the collector lead of T3 and T4 from both T1 and T2. To get it to expand and cause reduced again. This final signal can connect out of the emitter lead of T1 or T2
The Q level of the filter is approximately A/4. The “A” is the amplifier rate of the T3 / T4. Which is equal 2R1 (R2 and R4 are equal), the Q of the circuit, it is about 500.
Since we use the complementary Amplifiers, So the signal has low distortion. This feature can be used as a modifier harmonic distortion sine before the distortion measure.
The middle frequency of the filter is set to f = 1 / (2?RC). From the items are in the makes the circuit, it is the middle frequency of 1 KHz. Both P1 and P2 to adjust the filter to get the highest output frequency.
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