Schematic Diagram

This preamplifier was designed to cope with CD players, tuners, tape recorders etc., providing an ac voltage gain of 4, in order to drive less sensitive power amplifiers. As modern Hi-Fi home equipment is frequently fitted with small loudspeaker cabinets, the bass frequency range is rather sacrificed. This circuit features also a bass-boost, in order to overcome this problem. You can use a variable resistor to set the bass-boost from 0 to a maximum of +16dB @ 30Hz. If a fixed, maximum boost value is needed, the variable resistor can be omitted and substituted by a switch.

With the schema shown in the following schematic diagram, both channels of this stereo preamp is constructed using  RCA CA3052 quad AC amplifier.  this pre-amplifier schema is featured with tone control (bass – treble). Make a similar schema to complete the other channel, since the schema for left and right channel are similar. To be high-fidelity, total harmonic distortion should be kept minimum, this schema gives less than 0.3% distortion level at  at 1-kHz testing signal with 1-V amplitude.  

Gain or amplification at 1 kHz is 47 dB,  and the tone control will curve the response with 11.5-dB boost at 100 Hz and 10 kHz at maximum bass and treble boost.  For minimum bass and treble knob position,  the attenuation will be 10dB  at 100 Hz  and 9dB at 10kHz. This schema is operated by a single ended supply for wider range environment. Inputs can be from tape recorders pickup or magnetic-cartridge phonographs.