Simple circuitry suitable for moving-magnet cartridges
Passive high-frequency equalization
In recent years, following CD's introduction, vinyl recordings are almost disappeared. Nevertheless, a phono preamplifier is still useful for listening old vinyl discs from a well preserved collection. This simple but efficient circuit devised for cheap moving-magnet cartridges, can be used in connection with both audio power amplifiers shown in preceding pages, featuring low noise, good RIAA frequency response curve, low distortion and good high frequency transients behaviour due to passive equalization in the 1 to 20KHz range. Transistors and associated components provide ± 18V supply to the op-amp, improving headroom and maximum output voltage.
PART list
R1=47K 1/4W Resistor
R2=100R 1/4W Resistor
R3=_6K8 1/4W Resistor
R4=68K 1/4W Resistor
R5,R6=2K7 1/4W Resistor
R7=_2K2 1/4W Resistor
R8=39K 1/4W Resistor
C1-C3=100΅F 25V Electrolytic Capacitors
C4,C5=47nF 63V Polyester Capacitors 5% tolerance
D1,D2=BZX79C18 18V 500mW Zener Diodes
IC1=LM833 Low noise Dual Op-amp
Q1=BC337 45V 800mA NPN Transistor
Q2=BC327 45V 800mA PNP Transistor
J1=RCA audio input socket