Circuit principle: the input signal via IC1-1, and external components of the fourth-order low-pass filter to vary the slope of 24db/oct low-pass processing (figure value fc 70
Hz, A 8.2dB) and then to the IC2 -1 center AC inverting buffer amplifier 10 times amplified output is greatly enhanced low-frequency signal with the original signal strength respectively, by C4, C3 into IC2-3 mixing process, mixed-signal output from the C5. Mixed control the amount of W low-frequency signal with the original signal, in order to ensure that when W Off Ends C5 of the output signal is authentic, this gain level set to 0 dB. Component selection: determine the low-pass cutoff frequency R, C error is less than 1%, R2 - R5 can pick from the error of 5% resistors are used 1/8W RJ series; non-polar capacitors CL series, C4, C4, C5 tantalum electrolytic; RC components selected from the best use of digital measuring table, IC with authentic TL084. When using this circuit will be between the signal source and the amplifier connected in series.