Hi-Fi Stereo Preamp Circuit

This Hi Fi stereo preamplifier circuit is built with TDA1054 IC from SGS. TDA1054 is a 16-pin DIL package and integrates 2 separate preamp circuits.
It is a low noise preamp with little or no problem in the building process.
The first half of the circuit (IC1a) it has an input sensitivity of 3 mV and has a frequency correction composed of C5, C3, R6 and R8. The bass signal coming from phono input is amplified while the high signal is attenuated.

The selection of the input signal sources is done with switch S1. P1 and P2 are parte of a double potentiometer. They control the high tones and bass. There is no risk of overdrive in circuit due to the passive nature of the sound control. P3 controls the volume of the signal fed to se second part of the circuit (IC1b) which functions as an operational amplifier.
P4 controls the balance between the left and right channels but in the schematic is shown only the preamp for one channel.
Both channel have a gain of 24 at the middle setting of P4. If P4 is set to one extreme end, the gain difference between the 2 channels is about 12 dB.
HiFi stereo preamplifier schematic



Input sensitivity at a frequency of 1 kHz and output of 775 mVeff

• phono: 3mV/50k
• tuner: 220mV/50k
• tape: 220mV/50k

• maximum output voltage: 2.5 Veff
• balance range = 12dB

Sound adjustment

• low: +/- 13 dB
• high: +/- 13 dB
• distortion: < 0.05%
• bandwidth: 20 Hz … 24 kHz
• signal to noise ratio: > 65 dB