Differential circuitry 2A3 single-end output machine, 2A3 Power Amplifier
Keywords: Differential circuit for input stage 2A3 single-end output machine
Differential circuit for input stage 2A3 single-end output machine
There are four major elements of the courage to make a sound. First, we must use a sound line, and then the sound of elements, the third is the excellent production process, and the fourth is high. Classic commodities are more complicated. And some use special components and self-developed transformers, the imitation is difficult.
In recent years, domestic electronic teshes have continued to have a burn-up boutique, such as 2A3, 300B, 274B, 845, etc., created a material foundation for making oysters. The author introduces a biliary power amplifier with 2A3 or 300B, although the output power is only a few watts, but as a small number of sound pressure in the household Hi-Fi player, because the input stage uses the differential use of general aspirations The amplified circuit, so the signal to noise is relatively high. The sound is clear, beautiful, plus single-ended output machine is strong, and the music is deducted, it is worth listening.
The line see the drawing, the input voltage amplification is a differential amplifying circuit consisting of VL, V2. This circuit is very superior. The domestic gallchard magnifier is used by this circuit. Get a grand prize at the International Audio Exhibition. Since the VL, V2 two tubes work in symmetrical state, the effect on the circuit is extremely small in temperature change, power supply fluctuations, external interference, etc., that is, the suppression ability of the common mode signal is strong, and the circuit operation is stable. The signal to noise is relatively high, the music background is very quiet.
The working principle of the differential amplifying circuit is as follows: The input signal is input from the gate input of V1, and the phase output, the phase of the output signal is opposite to the input signal. Since the operating mode of the single-ended output is not used, the output of V1 is not used. The input signal of the V2 is injected from the cathode (8 foot), which is due to VL, V2 shared cathode resistance, an interpatch, and the amplified signal is output from the screen; the phase of the output signal is the same as the input signal, V2 works The magnification of the differential amplification circuit of single-ended output is 1/2 of single-tube, in order to have sufficient voltage gain, this grade magnifier 12AX7 can also be used with a five-pole voltage. Such as 6J1, 6SJ7, etc. The value of the cathode resistance R2 is large, and there is no bycoming capacitor, so the current is negative feedback. And the feedback is deeper. Work is very stable. The gate of the V2 also includes a loop negative feedback voltage from the push-level output. The feedback amount is determined by the resistance magnitude of R4 and R14. This circuit component is less and superior in performance.
V3 is the promotion level, with power amplification tube 6P3P (6L6), this gallbladder is large, and the sound is heavily. Promote the post-level power amplifier tube, you can get better results and bright tones. In order to reduce the internal resistance of 6P3P, it is connected to the form of a triode, and the ability to drive is stronger, and the appropriate amount of voltage feeds back to the gate of V2, so that the tone of the whole machine is more beautiful, the gate of V3 is equipped with R6 to inhibit parasitic oscillation.
The amplifier stage is used with a straight-heat tripathy power pipe 2A3 to get a extraordinary music performance. The power amplifier is working in a Class A state, and the self-bias work mode. The balance potentiometer W2 is provided at both ends of the filament to suppress communication. If the power amplifier tube is used to switch 300B, the other elements do not need to be more necessary.
The power supply section, B + high pressure uses a courage and choke CLC filter circuit. Take the tube 5AR4. This timid dynamic is better than other commonly used rectifier. The effect of the excellent and disadvantage of the whole flow tube is not absained by the magnifier; all the filaments are powered by AC;
The cathode circuits of V1, V2 require B-voltages, which can be powered by a battery of 1.5V. Another switch is responsible for the opening of B-power supply. Due to V1, V2, the operating current is small (2 mA). Therefore, the power consumption is not large, and the first battery can be used for 1-2 months, the sound is very transparent, sweet, and the signal-to-noise ratio is high. This machine is used in another set of B-power, adjusting W3, causing VL, V2 cathode (3, 8 foot) voltage to 1.5-1.8V.
To get a good playback effect, increase investment in components. Electronic tubes 2A3, 6P3P, 5AR4 have a wider, 12x7 selection surfaces, 12AX7WA and 5751 have tried; if you use ECC83 better. B + Source Capacitors use Mallory or Philips electrolytic capacitors. AB carbon resistance and domestic RT type carbon film resistance, B + circuits are sprague wound resistors. The capacity of the power transformer is large enough. At least 180 ~ 200VA, the capacity of the secondary high voltage windings is not less than 200mA, the output transformer is the key to the sound, the dawn 300b or 2A3 dedicated output transformer primary impedance 3.5kΩ The secondary impedance is 4Ω, 8Ω, and 16 Ω. The volume potentiometer should use the resistance stage to enter the variety of generic carbon film, this machine uses a 23-handage resistance level and is soldered with a US-feeding CGW resistance and silver-containing 6% Osel tin wire. The power fuse is to pass all power. Don't ignore, you can't use the normal home fuse tube, this machine uses the UK BUSS card fuses developed for audio equipment. The chassis uses a professional-processed stainless steel chassis, the chassis is preferably used in a non-conducting material, and the thicker, the thicker, and the thicker the sound after the load.
This machine uses a shed welding. It should be noted that the amplifier of the output of the straight-heat tripathy, there will be a large exchange of exchanges; therefore, pay special attention to component ranking and walking Lines, wires or components with AC magnetic fields should be remote from the signal transmission line and the on-screen power line of the large tube to avoid interference.
Whether there is a good voice and the work point of the school, especially the work point of the electronic tube, the impact of the voices is particularly large, so it is necessary to try the effect of different work points when debugging each work point can we find good Voice.
The negative feedback has a large impact on the mushrooms of the Senang and the whole machine. Adjust the resistance value of R14 and R4 makes the tonic. When the gain of the whole machine is enough, the sound is talented. More importantly, the Quality of R14 is because the feedback voltage is R14 to the gate, and when the Quality of R14 is high, the tone of the whole machine is more than the ship. Negative feedback resistance use antique AB carbon displacement or domestic RT type carbon film resistance. Apricot is more sweet than gold film resistance.
V1. The V2 of the cathode resistance R2 is large. The differential amplification circuit has a deeper current negative feedback, which has an impact on this level. When the resistance of adjusting R2 makes the input stage have sufficient gain, it is also possible to fully utilize the difference between the differential amplification circuit on the common mode signal, so that the signal to noise ratio of the whole machine is higher, and the tone is also more clear.
Golden is the simplest, most effective, and the most effective. 12AX7 for use in the UK Mullard or Sidide Telefunken ECC83, 6P3P switching 6L6GC or 5881, 5AR4 with 274b manufactured by Tianjin, etc. will have extraordinary sound performance.
There is still something that can't be mentioned, that is, the signal line connected to the sound source is also sufficient, and the sound quality will be more super.
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