What is the reason for the loud communication of power amplifier?

by:Gisen     2019-12-27
The reason for the large AC sound of power amplifier: Reason 1: common impedance interference of ground wire: all wires have resistance, and current has voltage drop through them. Reason 2: interference of power supply, almost all amplifiers are powered by AC power. No matter what kind of filter capacitor is used, ripples always exist. Fortunately, single-ended amplification is rarely used at present, and differential circuits have a great inhibitory effect on the ripple of power supply, therefore, there are fewer problems in this area. The third reason is electromagnetic and spatial interference. There is mutual inductance and inter-line capacitance between wires, which will interfere with the line. When wires pass through alternating current, alternating electrical and magnetic fields will inevitably be generated nearby. Wires are in alternating electrical and magnetic fields, the electromotive force is also sensed. When the current of the interference source wire is larger, the higher the working frequency and alternating potential amplitude, the higher the impedance of the interfered circuit, and the more the induction is. Power amplifier AC sound processing method: first, power supply and grounding point processing many power amplifier filter capacitors are too small, there are four only l0000μf, and at both ends of the tool and a 0. The CBB capacitor of 22μf can not only reduce the AC sound of power amplifier in static state, but also improve the transient strength and high frequency resolution of power amplifier in large dynamic state. Some power amplifier still has AC buzzing sound even after the above treatment, which may be due to improper grounding points. Generally, the grounding points should be selected near the filter capacitor and the 'one-point grounding method' should be adopted. Second, the output stage, if the static potential of the output stage deviates from the zero point, it will produce a great buzz. At this time, it may be a zero-adjusting resistor or a problem with the output pair, the output point potential of the power amplifier can be carefully adjusted, which should be below 100mv. If the zero point is not adjusted, some components of the power amplifier, such as the tube, should be carefully checked for damage. Third, the front amplification part, first short-circuit the input end of the front amplification part to the ground to see if the noise disappears. If the noise disappears, it can be determined that the noise comes from the input signal line, it can be replaced with a three-core Shielding Wire. Note that the shielding layer can only be grounded at one end. In addition, the coupling capacitor should choose capacitors with small leakage, such as tantalum capacitors, MKP capacitors, etc. , and the volume potentiometer housing should be grounded. There are also some power amplifier enthusiasts on the internet who have compiled some incomplete power amplifier communication sound processing methods: 1. Adding negative feedback can suppress the communication sound. 2, even if the negative feedback is screaming, it must be connected to positive feedback. 3, plus negative feedback howling may be because the circuit phase shift is too large, you can remove the feedback capacitor. 4. The feedback connection should be shielded and grounded at one end of the input terminal, otherwise it will scream. 5, the feedback of the left channel is connected to the right channel, there will be a howling. 6. If the push-pull tube is not paired, it is easy to have communication sound. 7. The feedback resistor is connected to the output terminal, and then connected to the cathode resistor with a shielded wire, so that the feedback resistor itself can be shielded without being shielded, and the noise will be lower. 8. Input RCA ground connection chassis 9 and filament connection balance resistor to reduce the gate negative potential by half and the frequency becomes 100Hz. In other words, adding balance resistor can reduce the AC sound amplitude, communication sound cannot be completely eliminated. 10. The direct heat cathode AC power supply is used as a single-ended Machine for AC sound compensation and AC sound compensation, that is, the idea is to take out the AC sound signal to be compensated, the opposite phase is used to compensate at the front stage of the power amplifier to offset the AC generated by the power amplifier filament. 11. The filament is converted into DC by a filter capacitor 20000 micromethod, or is powered by a DC external power supply. But the sound has become ugly, and it is better than listening with communication! 12. Power the filament with positive and negative DC power supply. In this way, the sound quality has the taste of communication. 13, tube or field effect delay voltage stabilization. 14. Set up a large grounding copper plate, and all those that need to be grounded will be grounded nearby. 15. The signal input stage unit is grounded and connected to the casing. 16, each unit (Or every time)All circuits are shielded with aluminum boxes, and the aluminum boxes are connected to the casing. 17, power cattle loaded silicon steel cover. 18. The filament circuit is suspended except for a little grounding. 19. The signal line and the return line are shielded lines, and the receiving interference amplitude is the same, the phase is opposite, and the anti-common mode interference is strong. 20. Signal line shielding layer single point grounding. 21. The internal live wire and zero wire of the power supply cable are connected to the Earth through the capacitor grounding wire. 22. power amplifier uses a three-wire plug, and the chassis is really connected to the Earth. 23, rectifier tube and small capacitance. 24, unreasonable wiring will also infect AC sound, the filament line should be close to the bottom version, do not parallel the power cord to the signal line. The power supply part cannot be too close to the audio input, and the feedback output two lines or the voltage amplification part is too close. 25, there is also a power transformer and output transformer coil winding difference of 90 degrees (A coil stands and a lie) This is to avoid mutual sensation. If there is a transformer cover with a good magnetic shield, there should be no problem! 26. The fixing bolts of the transformer should be grounded. 27, the front pole cathode resistor is connected in parallel with a capacitor 28, and there is the problem of the transformer itself! There should be a shield between the primary and secondary! Together with it, the grounding effect will be better! 29. The shielding layer of the signal line can only be grounded at one point, which is very important. 30. The potentiometer Shell should be grounded. 31. Short-circuit the voltage amplification grid leakage resistance to the ground with an electrolysis to see if there is any change in the AC sound, and the AC sound completely disappears, indicating that the voltage condenser tube produces AC sound, if only there is a change, it shows that there are communication sounds in the first and second levels. 32. Raising the filament potential of the voltage condenser tube can prevent breakdown between the cathode wires, and is also conducive to reducing the AC sound of the filament and the cathode leakage. 33. The lead of the gate should be as short as possible, and the Shielding Wire should be used. 34. The screen output is shielded wire, and one end of the shielding layer is grounded, preferably at the input end ( El84c likes, but zhainm version likes to follow the signal to ground at the back end) 35. Also set the grounding point at the RCA input socket. 36. The signal of each pipe is used as a grounding point at the negative level of the pipe. The peripheral resistance and capacitance are connected to this point by wire, and the bus is not used. 37. All power filter decoupling capacitors are connected to a total grounding point with wires, and do not use bus bars. 38, all lines, resistance as far as possible against the chassis (Roof) Fixed 39. Connect the signals of each pipe to the total grounding point 40 separately, and input the ground of the advanced Volume potentiometer of RCA, then connect to the negative level of the first-stage voltage condenser tube 41. If the filament does not have a tap, use two 47 ohm resistors and come out to ground.
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