Circuit of RIIA phono pre-amplifier with op-27
The op-27 is used in that circuit as phono pre-amplifier for your characteristic of low noise.
He only contributes with 3.2nV/√HZ of noise tension and 0.45pA/√HZ of current noise to the circuit. To minimize the noise of other sources, R3 it is configured for 100©. That generates tension of noise additional of only 1.3nV/√HZ. R1, R2, c1, and c @ form a net RIAA of a lot of precision with standard components supplying the necessary constant of time of 3180, 318 and 75µsec. For initial equalization and stability, resistors metal-film and capacitors of film of polystyrene or polypropylene are recommended.
Capacitor C3 and resistor R4 forms a simple filter of -6dB for octave, with cut to 22Hz. That circuit is capable of very low distortion on the entrance sign, usually below 0.01%. To 3v of total harmonic exit produced distortion is smaller than 0.03% in the frequencies above 20KHZ.
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