Make 100W power amplifier driven by TDA7250

When making a power amplifier circuit, the most headache problem is the transistor pairing and zero drift of the differential circuit. One accidentally rushed the power amplifier tube ... Now you can try the TDA7250.
TDA7250 is a power amplifier driver IC produced by SGS-THOMSON. Its features are as follows:
· Simple peripheral circuit and convenient production;
· Support wide voltage range: 2V-90V (± 10V- ± 45V);
· With zero drift control circuit without temperature compensation;
· Power transistor overcurrent protection;
· Squelch / standby function;
· Low power consumption;
· Low harmonic distortion: PO = 40W, fo = 1KHz, harmonic distortion = 0.004%
· Output power 60W / 8Ω, 100W / 4Ω.
The following is the application circuit diagram:

It can be seen from the above circuit that the over-current protection principle of the TDA7250 is to detect the voltage of the resistors R11, R12, R13, R14. When the overcurrent of the transistor, according to U = I · R, it is obtained that the terminal voltage of the resistor increases accordingly. After reaching a certain voltage, the TDA7250 will set the voltage of the base of the transistor to zero, so as to achieve the role of transistor overcurrent protection. Resistors R14, R15, R16, R17 are negative feedback loops, the gain of the entire circuit is determined by the ratio of R14, R15 and R16, R17, the formula GV = 1 + R14 / R16 or GV = 1 + R15 / R17.
The following are the PCB diagram, component arrangement diagram and PCB diagram sent to the PCB board factory for processing.

The above circuit has another use for audiophiles: to compare the differences between different power tubes. I happened to have MJ11032 / 11033, MJ11015 / 11016, 2SC3055 / 2955, 2SC4278 / A1633, 2SB522 / D522, TIP142 / 147 and so on, so I tried one by one. The speaker is a 12-inch box of Feida. The results are as follows:
The first to listen to is MJ11032 / 11033, which is transparent and bright for the treble of the tube, the midrange is full and full, the lip and tooth sound is clear and audible, the bass is more powerful and flexible, after listening to its bass, I feel that other pairs of tubes The bass is worse, especially 2SC3055 / 2955 and TIP142 / 147 are even tasteless; MJ11015 / 11016 is worse than MJ11032 / 11033 in high, medium and low bass, especially in the strength of bass and the overtone of treble; 2SB522 / The sound of D522 is relatively pure, and the sense of low volume is worse than that of MJ11015 / 11016, but it is better than MJ11015 / 11016 in the overtone of treble; 2SC4278 / A1633 is generally similar to 2SB522 / D522, and the treble seems to be better than 2SB522 / D522; / 2955 and TIP142 / 147 feel very bad, I do not know whether to buy genuine. The above are my personal ears and psychological feelings, for reference only.

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