Audiophiles are endless in their pursuit of audio sound quality, especially the pre-amplifier circuit, hoping to get a more pure music background and better sound quality.
To make a high-quality power amplifier, you must first have a superior preamplifier circuit, and a good preamplifier circuit to play its best performance, you need an excellent power supply to power it! Some Hi-END-level preamps are powered by dry batteries. For example, the Panasonic SU-C7000, the first-class power amplifier in Japan, is battery-powered! The domestic circuits of award-winning machines are mostly composed of discrete components. Figure 1 is a noise comparison diagram of three power supply systems: voltage regulator IC, discrete voltage regulator circuit, and battery.
Here, I will introduce to the enthusiasts the most widely used Class A parallel voltage regulator circuit in the domestic award-winning machine. The circuit diagram is shown in Figure 2. Using this circuit to supply power to the pre-amplifier circuit, the background is very quiet, which makes the low-frequency control force better, and there are Intensity, mid and high frequencies become smooth and soft, which greatly improves the music. It feels more gentle on the subjective sense of listening, without some coolness, harshness. Using this power circuit to motor, it can have an immediate effect, sound quality The improvement is obvious! Because the general audio mostly uses three-terminal voltage stabilization or series voltage stabilization, some use active servo voltage stabilization, and the performance of the class A parallel voltage stabilizing power supply circuit is closest to the performance of battery power supply, and the effect is of course remarkable!
The internal resistance of the parallel type stabilized power supply is very small, which plays a great role in improving the sound quality, because in the music signal current loop, the smaller the internal resistance of the current loop, the better! Laid the foundation for the reproduction of music details.
Let's analyze the working principle of the class A parallel stabilized power supply: 220V mains is filtered by the transformer after being stepped down by the rectifier bridge and then rectified by the C1 (C2) filter to filter out AC clutter, and then composed of LM317 and R1 with superior performance The constant current circuit (about 160mA, enough to drive any pure class A preamplifier circuit, if the current is larger, you can change the resistance of R1), the constant current circuit can block the power supply noise and effectively decouple The interference of the rear stage to the front stage through the power supply. The power supply after the constant current is composed of VT1 (VT2), VD1 (VD2), RP1 (RP2), R2-R5), etc. The voltage error sampling setting circuit is formed by Control the base of the adjusting tube VT3 (VT4), change the conducting voltage drop of the adjusting tube, and use the shunt current to achieve the purpose of voltage regulation. The adjustment tube and the load are connected in parallel, and the resistance is very small.
During production, the constant current source (LM317T) and the adjustment tube should be installed on a larger radiator (note that each tube and radiator should be insulated with mica sheets). Selection of components during author's production: The power supply is the key part of the performance of the pre-stage, so it is necessary to make enough use of it. The positive and negative power supply rectifier uses a 1A rectifier bridge, and the filter capacitor uses Japanese famous brands such as black diamond, ELNA, Ruby, Panasonic, etc., electrodeless capacitors use Panasonic CBB metalized non-inductive capacitors or Dutch Thomson MKP capacitors, resistance: R1 uses 2W or more metal film resistors, the remaining resistance is imported 1 / 4W five-color ring metal film resistors For low-power transistors, use the low-noise sound tube A970, and medium-power ones also use the sound tube C2073. The potentiometer for adjusting the output voltage cannot be used for ordinary products. You must use a precision potentiometer (the market price is 6- 8 yuan / piece). Of course, good components must be equipped with good circuit design: the author uses epoxy glass fiber circuit board and silver plating process.
Commissioning: Welding correctly and connecting to a transformer with suitable voltage, it can be powered on and debugged (Note: The voltage of the transformer must be equal to or greater than that required by the pre-amplifier): Use two digital multimeters to connect the positive and negative power supplies respectively The output terminal measures its output voltage, and then adjusts the precision potentiometers in the positive and negative power supply circuits to make them stable at the voltage required by the previous stage circuit, and the positive and negative power supply voltages are equal, then the front stage can be powered Now!
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