Transistor type B power amplifier with transformer as output

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Crystal oscillator

Photocoupler

There is a saying in the audio fever ring that the sound of the amplifier is soft and resistant because of the use of the output transformer, and the same conclusion can be drawn from the hysteresis loop of the silicon steel sheet. Coincidentally, the world famous Mai Jingtu is an established factory that produces audio power amplifiers. The plant's high-quality tube power amplifiers and transistor power amplifiers are well-known. Its transistor amplifiers feature a special high-quality auto-coupled output transformer. The ordinary transistor power amplifier components produce a sweet and audible tone. The output transformer is indispensable.

The author is inspired by this. Experiment with a transistor amplifier at home. Disconnect the speaker cable of one channel. Connect a megaphone with a power of 10W and a secondary impedance of 8Ω. Experimenting with one channel is good for comparison. Start listening.

The sound of this speaker with the wiring transformer has a great change. The sound softness is similar to that of the tube amp, the bass positioning and the strength are better, and it is very resistant. Experimental results show. A transformer is used as the output in the transistor power amplifier. It does improve the tone. So the author refers to the relevant information. Several transistors, integrated circuits and field-effect power tube amplifiers with transformers were produced. The sounds have their own merits. It has the same sound quality as the amplifier and the high efficiency of the transistor power amplifier. I am sending it to make an article. I hope that your newspaper will introduce it to audiophiles and look forward to correcting the same age. The power amplifier circuit is shown in Figure 1.

The components are basically eliminated from the replacement of China's electronic military enterprises, with high quality and low price. Among them, the input, output and power transformers have a significant impact on the performance of the whole machine.

Input transformer

The 22mm×32mm EI type silicon wafer core is used, and the sheet thickness is 0.35mm. The primary uses φ0.21mm enameled wire wrapped around 1500匝, and the secondary uses φ0.23 mm enameled wire around 190匝×2. Because there is a unidirectional DC pass. The silicon steel sheet is inserted. A 0.15 mm thick kraft paper pad was used as an air gap between the E and I sheets to avoid magnetic saturation. Since the supply voltage of the transistor is very low, the author uses a random winding method. After the primary winding, the two layers of kraft paper are wound around the secondary, and the secondary double wires are wound together. Pay attention to the same name when wiring. See Figure 2.

Output transformer

It adopts 30mm×50mm EI type large window high silicon core, the window height is 53mm, the width of the window and side column are 19mm. See Figure 3, the thickness is 0_35mm, the primary is φ0.86mm enameled wire winding 250匝×2, secondary With a φ0.90 mm enameled wire wound 350 匝, the silicon steel sheet is inserted without leaving an air gap. The skeleton is divided into two by a partition from the center. Two push and pull two wire packages are separately wound. Conducive to symmetry and reduce distributed capacitance. Pay attention to the same name when connecting, as shown in Figure 4.

Power Transformers

The power is 200W, and the 45mm x 60mm EI type high silicon core is used. The sheet thickness is O.50mm, the primary is φ 0.77mm enameled wire wrapped around 570匝, and the secondary is wrapped with φ1.30 mm enameled wire around 74匝.

Assembly

Two 3AD18 power tubes and two 3AD18 power supply adjustment tubes are respectively added with 100mm × 200mm and 2.5mm thick aluminum plates for heat dissipation. Pay attention to the insulation treatment between the shell and the aluminum plate during installation. The circuit is divided into two parts: the main board and the power board. You can draw by yourself according to the conditions. The heat sink is also mounted on the board. Each transformer is installed near the circuit diagram.

debugging

Adjust the BGl base 1.8KΩ resistor so that the BG1 quiescent current is 2.5-3mA, the collector voltage is 4V. Adjust the BG2 base 470n resistance. The quiescent current of BG2 is 50-55 mA, the collector voltage is 18 volts, the quiescent current of BG3 and BG4 is 0, and the collector voltage is 24V.

Audition

After testing, the output power of this machine is 25W, and the frequency response is 30~10000Hz. The audio signal is directly connected from the CD player, and the amplifier is used to push a pair of 88dB three-way audio. The bass is thick and powerful, the sound quality is pure, the soft and beautiful, very resistant, and interested enthusiasts may wish to try. Will not disappoint you. However, compared with the tube power amplifier, the high-pitched part is lacking. After all, the 3AD18 has a lower characteristic frequency. Why not use a 3DD-type silicon triode with a high characteristic frequency? Because the neon tube is more symmetrical than the silicon tube. It’s much better to listen.