Simple Phono Preamplifier

This circuit shows that a preamplifier for magneto-dynamic cartridges can be relatively simple without seriously com- promising compliance to the IEC stan- dard in respect of frequency response. Compared to the RIAA standard, the IEC frequency curve has an additional roll-off point at 20 Hz-see Fig. 1. The circuit diagram of Fig. 3 shows that input and output of the preamplifier based around the Type TL071 oper- ational amplifier are direct coupled, making it possible to accurately define the previously mentioned roll-off by means of network R2-C3. Output offset of the preamplifier is about 3 mV. Output capacitor C4 can be fitted if this offset voltage can not be handled by the input of the line or power amplifier. For optimum compliance with the IEC frequency curve it is recommended to use close tolerance polystyrene (Siemens Styroflex) capacitors in pos- itions C: and C2, and an MKT capacitor in position C3. Resistors are preferably high-stability metal film types from the E48...