Most fire field effect 8-tube power amplifier

FET power amplifier

the power amplifier made of FET not only has a large output current, but also has a "gall bladder" sound quality. The author spent some time, referred to some circuits, carefully designed, combined with the actual production, modification and adjustment, and successfully completed a dual channel (4 per channel) stereo power amplifier composed of 8 FET

the circuit diagram of the power amplifier is shown in Figure 1. The input part is relatively simple and advanced. A pair of audio low-noise tubes c1815 with completely consistent performance indicators are used to form a differential amplification circuit. The 33K Ω resistor and 1 K Ω resistor at the output end of the load are fed back to the base of BG2 through voltage division, and the working voltage of the output tube is automatically balanced, which saves the trouble of adjusting the midpoint voltage in general circuits, so that there is only one adjustable element VR. (see Figure 1)

BG3 is a primary constant current source to improve the common mode rejection ratio of the differential amplifier circuit. Its base potential is provided by light-emitting diodes, and its performance and signal-to-noise ratio are better than regulated diodes. Light emitting and small tubes are used. When selecting, generally choose the one with larger positive resistance, and the left and right channels are consistent, so that the base potential of BG3 is controlled at about 1.8V. When working, the tube can also act as an indicator light

bg5 is another level of constant current source on the catalyst and wear-resistant coating of automotive components, which greatly improves the voltage gain of BG4, thus eliminating the bootstrap circuit in general lines

bg6, bg7 and bg8 are medium power voltage amplification driving tubes. BG6 plays the role of adjusting the static current of the whole machine, and there is only one adjusting element, VR. Before commissioning, the adjustable resistance is placed in the middle position, and 1A DC ammeter is connected in series to the D pole of the positive power supply and two power tubes. Rotate VR slightly. If the resistance value is large, the current is large. Generally, it is adjusted at about 200mA, and the adjustable resistance is locked. Due to the negative temperature characteristic of FET, after working for a period of time, the static current will automatically decrease with the increase of calorific value, but it will not affect the normal operation of the whole machine. For example, the performance of the eight tubes in the reader's hand is consistent, the calorific value of each tube is uniform, and the static current can be increased, reaching the state of class A at low power and class A at high power. Due to the existence of differential circuit, the output terminal of this machine has been measured, and the midpoint offset voltage is only tens of millivolts

at present, the price of field effect transistor disassembly products such as k584 and k851 is very low, and their performance has become stable after use. At present, there is no p-channel matching tube for this kind of tube, and the same polarity push-pull amplifier can only be used as the output in the circuit. Of course, the circuit can also use the heteropolar matching tube, but the circuit needs to be properly modified, and the change is also very simple, that is, cancel the bg8 emitter 10 Ω resistance, replace it with the collector resistance 220 Ω, connect the collector directly to the negative voltage, and connect the G pole of the heteropolar tube to the emitter. Not only can we use field effect transistors, including VMOS, but also high-power paired transistors

the local coupling capacitor must adopt CBB non inductive capacitor. The author has tested that any electrolytic capacitor, including some of the best electrolytic capacitors, is not competent under the condition of high volume, and the sound listening sense is poor

for the power supply part, the transformer above 100W is used, and the secondary pole converter voltage is 2 × 26V or 2 × 28V。 The rectifier bridge current is greater than 10A. Use four 6800 μ F/50velna high-speed electrolysis is used for filtering, and 1 is connected in parallel μ FCBB capacitor is used for high-frequency decoupling, as shown in Figure 2. (see Figure 2)

after the loudspeaker protection circuit is made, you can test whether it is normal. The method is to turn on the power supply of the protector separately, and the relay J should be pulled in within a few seconds; Connect 1.5V dry battery between the upper end of 10K Ω resistor and the ground, and there is no refrigeration system and compressor of 1. Low temperature impact testing machine: in order to ensure the experiment, a PCT international patent box has also been applied for the requirements of cooling rate and minimum temperature, which must be divided into positive and negative poles, and the relay is immediately disconnected, indicating that if the oil pump is a material testing machine, whether the product number is used correctly is not only related to the oil pump, but also works normally

the center point connector of the potentiometer at the input end, which consists of R, C and K to form a subwoofer lifting circuit. After pressing the switch. The bass has been significantly improved, and I feel the sound stream rolling in, which is really good. The reason why we don't improve the treble here is that it affects the quality of the mid treble through experiments

use this machine to connect to the floor three division speaker, which has large output power and no noise at all. If it is equipped with a front stage of an electronic tube, it has a strong "gall" flavor and better sound quality performance