360W×2 amplifier production

1. Design concept and implementation method

(1) It can drive 4Ω, 2Ω and other double bass "big food" speakers and various professional boxes with professional large and thick voice coils.
(2) It should save power, have low noise and low heat generation.
(3) The sound quality should be good and suitable for home and professional use.
　　 The realization of the first point is to have a large driving power. Due to the current trend of expanding living room area, amplifiers below 100W ×2 have become somewhat "incapable", so this amplifier is designed to be 360W ×2 at 4ΩQ and 720W ×2 at 2Ω.
　　 The realization of the second point is that the circuit works in a static Class B small current, relying on large pond-level capacitors and resistors for filtering and noise reduction, so that the amplifier-level noise is extremely small. The working state of the circuit determines that the heat generated by the circuit components is very small, which is equivalent to that of general Class B circuits. The large heat dissipation system is equipped to cope with the safety and reliability of continuous high-power and low-impedance output.
　　 The realization of the third point is the main goal of this amplifier board. It is generally recognized that Class A, MOS, and electronic tubes have good sound quality, so this amplifier should achieve the sound quality of Class A, MOS, and electronic tubes.
2. Realization of high power output
　　 To achieve high power, the power supply capacity must be large. The power supply configured in this amplifier is a ring transformer wound on a ring core with a cross-sectional area of ​​35mm × 60mm. The primary side is 1.0mm wire wound 484 times, and the secondary side is 1.5mm double wire wound 100 times.
　　 The rectifier is two 40A full bridges for double bridge rectification, and the filter is 4 47000 uF capacitors + 2 2.7kΩ resistors connected to the positive and negative power supplies to stabilize the voltage at ±62V. If the voltage is too high, the resistance can be reduced to 2.2kΩ, and if it is too low, the resistance can be increased to 3kΩ, and the power is more than 3W.
　　 In addition to the power supply, to achieve high power output, especially to drive the "big food" speaker, the power amplifier output current capability must be strong. This power amplifier uses 6 pairs of 2SD1037 tubes for quasi-complementary output per channel, which can drive the "big food" speaker with a DC resistance as low as 0.5Ω. Therefore, 360W×2 at 4Ω and 720W×2 at 2Ω are guaranteed.
III. Implementation of the concept of green environmental protection
　　 For this power amplifier, low power consumption, low noise pollution, and low heat radiation pollution are achieved through the following measures:
(1) When this power amplifier is unloaded, it only works at a small current level, and the base voltage of the power tube is only 0.45V, which is basically cut off, so it consumes less power than the general Class B and is a power-saving power amplifier.
(2) Due to the above-mentioned static principle, this power amplifier has low heat, so the heat radiation is very small. The noise is even smaller. Even if you put your ear against the speaker, you can only hear a slight "hissing" sound, which is smaller than the noise of ordinary headphones.
4. Realization of Class A, MOS, and Tube Sound Quality
　　 At present, it is generally recognized that Class A, MOS, and tubes have the best sound quality, so this power amplifier circuit is designed to work in the best state of Class A when it is dynamic, and the bias current increases and decreases synchronously with the signal size, so the sound quality is technically guaranteed. In this working state, even if a few general MOS tubes are replaced, the improvement of the sound quality is not obvious. The schematic diagram is given below, as shown in Figure 1. It can be seen from Figure 1 that this schematic diagram is quite simple and saves more components than the general Class B or Class AB quasi-complementary circuit. And by changing the connection method of a resistor on the circuit board, it is convenient to switch between this circuit and the quasi-complementary Class B or Class AB.

Below: Circuit Principle

Figure below: Power supply

　　 Due to the simple wiring of this amplifier board, it is easy to make by hand. The author uses a carving knife to make the bottom board lines and drills Φ1.2mm holes on the solder joints, and welds them with copper rivets with an inner diameter of Φ0.8mm, making this circuit board a "pure earth artillery" level production, and can be double-sided welded and repeatedly welded without damaging the circuit board, which brings great convenience for repeated adjustment and replacement of components. Two "pure earth artillery" amplifier boards are shown in Figure 2, and four power tube shunt boards are shown in Figure 3. The component parameters are listed in the attached table. As long as the construction is carried out according to the drawing, the parts are qualified, and there is no adjustable resistance.

Below: Pure earth cannon amplifier board

Below: Power tube shunt plate

　　 The following points should be noted:
(1) The electrolytic capacitors used on the board can be domestic CD26 type, and tantalum capacitors should not be used, so as not to affect the layering and high frequency. Audiophile-grade capacitors are better.
(2) Both the 20pF feedback capacitor and the 300pF capacitor should be 100V domestic mica capacitors, and ceramic or polyester capacitors should not be used, so as not to generate noise and phase shift.
(3) 0.047uF capacitors can be polypropylene varieties, and polyester varieties should not be used, so as not to disperse and soften the high frequency.
(4) The transistors used are all commonly used varieties. If other models are used, please pay attention to the component parameters and safety.
(5) The more accurate the values ​​of all components on the board, the better, especially the resistors and paired tubes.
(6) Since the final stage uses up to 24 power tubes, the heat sink should be large. I used a 35mm×100mm×450mm black aluminum alloy heat sink for each arm (6 pieces) and fixed it on a top cover made of 730mm×480mm aluminum plate. When playing with a 4Ω or 2Ω speaker, it was still "cold" after a few hours at normal volume.
(7) All data tests of this amplifier were measured by DT890B digital multimeter.