Internal circuit of STK3048 and 6153

It is a loOw power amplifier circuit composed of ST K30 48 and STK6153. It uses 1/2STK3048 as preamplifier
and drives it directly. STK6113, and l/2 ST K30 48 for DC servo circuit. It not only makes the best use of everything, but also
improves the performance of the circuit. The signal output by the power amplifier is filtered by the RC circuit and the detected DC drift signal is input to pin 1 of IC3 . After being processed by IG, the zero point correction signal is output from pins 5 and 6. This signal is input to the inverting input terminal 14
of ICI through a 22kn resistor.
pin, so that the amplifier's output zero-point potential is accurately controlled within the required range.
The 0.39fl non-inductive high-power resistor at the lower end of the speaker is the sampling resistor for the speaker voice coil current. Its function is to
sample the DC feedback signal. The feedback signal current is input to the feedback input terminal of Icl through the 22kfl resistor. The 2200 resistor connected in parallel with the speaker is
designed to prevent the amplifier from self-excitation when it is no-load.
    In the circuit, capacitor C3 has a significant impact on the sound quality. When the island is 1vF, the frequency response of the circuit is less than 9kH, the treble
is severely suppressed, and the sound is dull. When the value of C3 is 0.1t,F, the frequency response is less than 12kHz, the treble is obviously insufficient, and the low and midrange
are prominent. When the value of C3 is 0.03ruF, the treble is bright and clear, and the full range performance is balanced. If C3 is cancelled, the sound becomes
dull.