The amplifier`s gain is nominally 20 dB. Its frequency response is determined primarily by the value of just a few components-primarily C1 and R1. The values of the schematic diagram provide a response of ±3. 0 dB from about 120 Hz to better than 20, 000 Hz. Actually, the frequency response is ruler flat from about 170 Hz to well over 20, 000 Hz; it`
s the low end that deviates from a flat frequency response. The low end`s roll-off is primarily a function of capacitor C1(since RI`s resistive value is fixed). If C1`s value is changed to 0. 1 pF, the low end`s comer frequency-the frequency at which the low-end roll-off starts-is reduced to about 70 Hz. If you need an even deeper low-end roll-off, change C1 to a 1. 0 pF capacitor; if it`s an electrolytic type, make certain that it`s installed into the circuit with the correct polarity, with the positive terminal connected to Q1`s base terminal.