This is a Simple G - Purpose Preamplifier Circuit Diagram. This amplifier is useful for audio and video applications. Gain is set by Rf and the voltage gain of this amplifier is approximately 1 + i//560, where R/vs, in ohms. Bandwidth depends on gain selected, but typically it is several MHz. R/= 5.1 KOhmhm, which produces a gain of 10 (20 dB) voltage.