DC servo constant current power amplifier 02

A few days ago, I purchased a DC servo constant current stereo power amplifier printed circuit board from a company . It uses the TDA1514A
integrated circuit, as shown in Figure 5-103. After listening to it, I immediately felt that its high frequency was rich and impetuous, and its bass was weak, giving people a dull and dull
feeling. In addition, it made a loud "chipping" sound when it was turned on and off. Later, although I consulted relevant electronic newspapers and made some
improvements, the sound quality was still not satisfactory. 6 Finally, in desperation, I restored the circuit to the circuit recommended by Philips,
put in the original record, and tried it immediately. I feel that it is different from the original. The low frequencies are expressed and appear to be flexible.
The distribution of high, middle and low frequencies of the music appears harmonious. The treble is no longer harsh but is still very clear. It eliminates the original dull and dry feeling, and
"porches" when turning on and off the phone. "The sound was almost inaudible. After listening like this for a few days, I felt that the low frequency was still not enough, so I
changed the low-end cutoff frequency of the AC negative feedback at point AB in Figure 5-104, which is better than the AC negative feedback network to quasi-AC negative feedback, as shown in Figure s- As shown in 105
. Because the low-end cutoff frequency of quasi-AC negative feedback is much lower than that of AC negative feedback, it is obviously slightly
higher than DC negative feedback, but its ability to maintain the zero potential of the speaker is one order of magnitude higher than that of DC negative feedback. After powering on, I used a digital meter to measure that
the output DC voltage was only about 3mV. I put the record on and listened carefully. I found that the bass dive was deeper than before and the treble was much more delicate. I was
not satisfied until then.