Homemade a front bile stone bass amplifier

DFN1006 TP-RCLAMP3321P ESD Diode Low Capacitance

In order to enhance the bass, a front-mounted bile stone bass amplifier was built. It works well with the original one-channel combined amplifier.

The circuit is shown above. The BTL power amplifier circuit is composed of two LM3886 integrated circuits. Use two 10" 8Ω speakers in parallel to form a 4Ω load, and achieve IOOW power when the power supply capacity is sufficient. BTI. There are several ways to input the signals of the two amplifiers in the circuit. I choose a fully symmetric dual signal input. This requires a pair of input signals with equal amplitude and opposite phase. The front stage of the machine consists of a 12AX7 bile tube differential amplification circuit, single signal input, dual signal output, equal amplitude, opposite phase, feedback low-pass active filter circuit composed of two 12AU7 bile tubes, which will be higher than 159Hz in the two signals. The component is attenuated and the bass band signal is output from the cathode, which matches well with the rear LM3886.

The signal input of this unit is taken from the left and right channels of the original power amplifier. Since the left and right channels each have their own ground bus, they are grounded at the power supply. If the left and right signals input to the unit are simply combined into one, and the signal grounds are also put together, the original circuit will form a large loop, destroying a grounding method and causing interference. To this end, an isolation circuit composed of two 4N35 optocouplers was designed at the front end. The two machines were electrically isolated. Two 12V power supplies were used to form two 12V power supplies, which respectively supplied power to the 4N35. By the independence of the 2 windings, the grounds of the input signals are made independent, and the problems caused by the joints are eliminated.

Because the coupling output of the original machine is added to the coupling capacitor, in order not to affect its DC operating point, plus the Cl capacitor is blocked. The resistance of Rl has a large influence on the low frequency waveform. Because the input signal is not a digital quantity but an analog quantity, in order to overcome the dead zone voltage of the LED, a suitable operating current is provided through R2, generally 5mA~lOmA is preferred, although larger is advantageous for linearity, but power consumption and noise. It will also increase, which is unfavorable. The power supply of the phototransistor is stepped down by a resistor and is regulated by a 24V Zener diode. The resistor R3 is to provide a suitable bias current to the phototransistor, otherwise it is always in a state of deep saturation conduction under illumination, and the tube voltage drop is small. The bias current is pulled back to the amplification region.

The power transformer of this machine is 500VA. The 32A rectifier bridge for low voltage power supply, the positive and negative voltage filter electrolytic capacitors are each 50000 ̈F, which is composed of multiple PHIUPS brand electrolytic capacitors. Considering that the commercial power allows IO% fluctuations, and the filter electrolytic capacitor is not fully symmetrical, the positive and negative voltages are asymmetrically unstable, and the voltage drop under large currents will inevitably affect the dynamic amplitude and symmetry of the output.

To this end, a high-power voltage regulation component composed of discrete components is added. The triodes in the symmetrical position are all complementary tubes, the magnification is selected to be substantially close, the heat sink is large, the power quality is greatly improved, and the dynamic distortion is effectively reduced.

Due to the large capacity of the filter capacitor used, the strong inrush current at the moment of powering will cause an impact on the rectifier bridge. To be safe, a buffer circuit is added, which consists of a 555 integrated block and a relay. Two models of JZX-22F42 small medium power relays were selected using the hand components. Each relay has 4 sets of contacts, each of which has a capacity of 3A/28V (DC), which is used in parallel to ensure the safety of the contacts. When starting up, two lOO high-power resistors act as a buffer, and the inrush current is greatly reduced. After a dozen seconds, a relay contact is turned on, the resistor is shorted, and the power supply is normally supplied.