Do you really understand the power amplifier circuit? These two most classic power amplifier circuits let you know what is the power amplifier circuit.

The internal pre-stage of the STK6153 uses a constant voltage source bias, which can better stabilize the operating state of the output stage. However, the quiescent current provided by the constant voltage offset between the STK61534 pin and the 1 pin is only about 10 mA. This leads to a certain degree of serious crossover distortion and high-pitched phenomenon of the power amplifier. In addition, the final current output area of ​​the STK6153 chip is much more amplified than the set of LM1875, TDA1514, so the internal resistance is smaller and the power margin is larger. However, the output form of the STK6153 open collector increases the output impedance of the amplifier, making the above advantages impossible. In response to the above defects, I gave up the STK6153's pre-stage offset, and the latter stage changed to the emitter output. At the same time, the UPC1225H was used to push the STK6153 for current amplification to produce a high-quality low-cost Hi-Fi amplifier. The specific circuit is shown in the figure.

The uPC1225H is a 50W audio driver circuit introduced by NEC. The chip has a perfect protection link inside. The peripheral circuit is slightly more complicated, but the output voltage deviation of the uPC1225H is only ±5mV. The extremely wide power band and extremely high slew rate make it It is warmer, softer and more resistant than the LM3886.

The accelerating capacitor C5 in the circuit diagram has a significant influence on the high-frequency output of the power amplifier, and the capacity should not be too large. It is best to use a CBB capacitor. T1 can choose any low frequency medium power NPN tube. Rw1 is the only component in the circuit that needs to be adjusted. By adjusting Rw1 to change the voltage between c and e of transistor T1, the bias voltage of the final output tube of the power amplifier can be fine-tuned. Under the amateur condition, the circuit is installed and the dummy load is connected after checking. After the static, the Rw1 is carefully adjusted with a screwdriver to minimize the output potential of the midpoint to the ground. The temperature rise of uPC1225H and STK6153 is relatively high, and a suitable heat sink is required.

The system also designed a set of speaker protection circuits composed of uPC1237HA. D1 uses a neodymium diode whose anode is connected to any AC output of the transformer secondary. Relay J1 is directly powered by the 24V voltage provided by the LM7824.

Practice has proved that the combination of STK6153 and uPC1225H takes into account the advantages of both, not only retains good low-frequency strength and F-dive depth, but the flexibility and high-frequency resolution of the power amplifier are significantly better than those of STK6153+STK3048A. improve.

STK3048 and STK6153 are thick film power amplifier integrated circuits from Sanyo Corporation of Japan. STK3048 is a pre-stage voltage amplification integrated circuit; STK6153 is a post-stage current amplification integrated circuit.

The STK3048 is a 15-pin dual-channel single-row thick film package with an exposed heatsink connected to the (8) pin but insulated from the internal circuitry. (8) After the ground is grounded, it has a certain shielding effect on the internal circuit. The thick film block does not have to be equipped with a heat sink when it is working.

The STK3048 has two internal stages, the input stage has a protected differential amplifier, and the two diodes on the base of the differential tube protect. Its collector's RC series phase compensation network prevents transient distortion in the input stage due to burst signals. A set of mirrored current sources are connected between the two collectors. The purpose of this circuit is to linearly invert the right input tube current and the left input tube to form two subtracted current sources, and perform current excitation on the latter stage. The main voltage amplification stage is a common base common-emitter circuit, the upper tube broadens the signal for amplification, and provides impedance matching for the direct coupling between the input and output stages; the lower tube linearly outputs the amplification current of the upper tube to reduce the opening of the stage. The ring is distorted and provides a large excitation power to the subsequent stage. The two-stage amplifying tube is supplemented by a constant current source as a load, and the power supply ripple suppression force is strong.

The STK6153 is a 10-pin mono single-row thick film package (two for two channels) and the internal circuitry is electrically isolated from the exposed heat sink. The STK6153 integrates a constant voltage source bias, a non-pre-stage push, and a non-composite current amplifier circuit. It adopts fully complementary symmetrical structure and has excellent characteristics such as high speed, high precision, high power and low noise. Due to the built-in constant voltage source bias, the unstaged high power tube is always in optimal working condition and has excellent temperature compensation. The complementary output of the thick film block is designed as an inverted Darlington composite circuit, which is output as an open collector to reduce the output impedance.

The power amplifier circuit composed of STK3048 and STK6153 is shown in Figure 3-41 (power supply and protection circuit are omitted), and the internal circuit of the front and rear stage IC is analyzed in the dotted line frame. The small capacitors in the front stage can be selected from German WIMA or ERO high-quality capacitors. The power supply filter is optimized with Nissan Marcon NIPPON, CHEMICON Nitsuko and Rubycon brand capacitors. Each large electrolytic unit is connected in parallel with a small WIMA0.1uF~0.33uF. Capacitors to improve frequency characteristics. The circuit can work normally without debugging. In the overall listening feeling, the frequency bands in the full range are very balanced, with large dynamic, wide frequency response, low distortion, fast transient response, pure and powerful sound quality, and extremely low noise. Circuit sinusoidal power; 2X100W, distortion.

The internal circuits of the STK3048 and STK6153 are relatively simple, and their sound quality is very good. However, the design of peripheral lines and the selection of peripheral components have a great influence on the sound quality of the IC. Therefore, the power amplifier uses the circuit shown in Figure 3-42.

1. Use Gm to control the volume, enter the volume potentiometer and connect it to the gain control point of IC3 (NE5532), and change its negative feedback depth to change the volume. The STK3048 works at its best steady state. There is almost no sliding noise when adjusting the volume. What's more important is that the dynamic range is still the same when playing at a small volume. At high volume, the details of the music are vividly displayed, without any feeling of muddy water.

2. Using constant current negative feedback circuit, the linear resistor R and R' variable amplifier constant voltage mode is used to drive the load in constant current mode, which improves the transient characteristics of the power amplifier and enhances the strength of the bass and the clarity of the high sound.

3. Cancel the loop negative feedback capacitor, IC4 (NE5532) and peripheral components constitute the output midpoint zero servo circuit. Used to servo the STK3048's 2, (14) feet, after canceling the feedback capacitor, it causes the DC potential of the STK6153 output to drift, improving the amplifier's high and low frequency resolution.

Subjective listening evaluation of the amplifier: the treble is slender and clear, the midrange is bright and clear, the bass is full and strong, the range is distinct, the harmonic distortion is small, the noise is low, and the dynamic range is extremely wide. Due to the large output power of the circuit, it should be noted that the power supply used must have sufficient capacity, and the STK6153 heat sink should not be too small. The op amp IC is powered by a separate active servo supply. In addition, the amplifier must be equipped with a speaker protection circuit

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