Design and production of NE5532+TDA1521 amplifier

Amplifier is a common and typical electronic product. It consists of three parts: DC regulated power supply, audio preamplifier and power amplifier (as shown in the figure below). The amplifier basically covers all the contents of the amplifier circuit, and is very comprehensive. Each part is an independent unit circuit. In this production, the audio preamplifier and power amplifier are taken as two projects, and the design and production are explained separately. Then some auxiliary circuits are added, connected together, and debugged. It constitutes a practical amplifier.

1. Production of audio preamplifier

The output signal of the microphone is generally only about 5mV, so it needs to be amplified without distortion, which is accomplished by the preamplifier. The preamplifier is required to have low distortion and wide bandwidth. The main technical indicators are as follows.

Voltage magnification: 10 times:

Passband: 50Hz～20kHz.

1. Circuit design

This project designs and manufactures the preamplifier of a two-channel amplifier. Each channel consists of two parts: a preamplifier and a volume adjustment circuit. The preamplifier is implemented by an integrated operational amplifier, and the volume control is implemented by a dual potentiometer.

The circuit is shown in the figure below. The integrated operational amplifier is NE5532.

NE5532 is a dual op amp, a high-performance, low-noise op amp with good noise performance, excellent output drive capability, and fairly high small signal and power supply bandwidth.

The circuit is a circuit with two same-phase input amplifiers. Through analysis, it can be known that the voltage amplification factor of the circuit is about 11 times, corresponding to two channels. The function of the 200k potentiometer in the figure is to ensure that the gains of the two channels are the same; the function of the double potentiometer is to adjust the output voltage of the two channels at the same time, that is, the volume of the two channels; the function of the voltage regulator is to ensure that the voltage of the power supply is ±15V; the function of the capacitor on the power supply is to eliminate the influence of ripple and high-frequency noise and prevent self-excitation; the capacitors at the input and output ends play a role in blocking DC.

2. Circuit fabrication

When soldering the circuit, please note:

(1) The dual potentiometer should not be fixed on the circuit board, but should be fixed on the casing during assembly as a knob for adjusting the volume.

(2) To ensure the balance of the two channels, the feedback resistor of one of the amplifiers can be replaced by a 200kΩ potentiometer. The resistance value of the potentiometer can be adjusted to ensure that the gains of the two amplifiers are equal.

3. Circuit debugging method

(1) Input the same small AC signal (Ui=10mV, f=1kHz) to the two channel input terminals, measure the voltages at the two output terminals, and observe the output voltage variation range;

(2) Adjust the 200kΩ potentiometer to make the output voltages at the two output terminals equal.

(3) Change the input signal frequency and record the output voltage amplitude. Find the frequency value when the output voltage is 0.7 times the maximum voltage and draw the amplitude-frequency characteristic curve.

4. Common problems and solutions during debugging

(1) No output voltage: Is the power supply connected? Is the voltage regulator connected in reverse or of the wrong model? Is there a signal at the input end?

(2) The amplification factor is incorrect: Are the resistance values ​​of the feedback resistor and the inverting terminal resistor incorrect?

2. Design and production of power amplifier

The main technical indicators are as follows: Output power: 2×12W; Frequency response: 50Hz～20kHz; Distortion: ≤0.5%.

1. Circuit design

This project uses the integrated amplifier TDA1521 to design and manufacture a high-power low-frequency power amplifier. TDA1 521 is a high-quality power amplifier integrated circuit, which adopts a nine-pin single-in-line plastic package. It has the characteristics of large output power, small gain difference between the two channels, no impact sound when the speaker is turned on and off, and reliable overheating, overload and short-circuit protection. The output power is 2×12W, and the distortion is ≤0.1%. TDAl521A can be powered by both positive and negative power supplies, and can also be powered by a single power supply. When powered by dual power supplies, two audio output capacitors can be omitted, and the sound quality of high and low bass is better. When powered by a single power supply, the power filter capacitor should be as close to the power supply end of the integrated circuit as possible to avoid self-excitation inside the circuit. When making it, be sure to install a heat sink on the integrated block before powering on and testing it, otherwise it is easy to damage the integrated block. The heat sink cannot be less than 200mm×100mm×2mm.

2. Circuit making power amplifier

The circuit is shown in the figure below. This circuit uses dual power supply. Note when soldering the circuit:
(1) Do not connect the TDA1521 power supply in reverse, otherwise the circuit will burn out.
(2) The heat sink should be large enough, not less than 200mm×100mm×2mm.
(3) Do not solder the speaker in the circuit. When assembling, the output terminal should be connected to the output terminal.
(4) To reduce noise, the power amplifier circuit and the preamplifier are soldered on the same circuit board and as close to the output terminal of the preamplifier as possible.

3. Circuit debugging

(1) Connect the power amplifier circuit to the preamplifier. Input the same small AC signal (Ui=10mV, f=1kHz) to the two channel input terminals, measure the voltages at the two output terminals, and observe the output voltage variation range;

(2) Adjust the dual potentiometer to measure the maximum undistorted voltage output by the circuit; (3) Measure the passband of the circuit.

3. Assembly of the Amplifier

1. When assembling auxiliary circuits, some auxiliary circuits need to be added:
(1) Input terminal white: left channel red: right channel
(2) Output terminal left and right channels, black terminal grounded;
(3) Switches, indicator lights, and fuses are shown in the figure below.

　　
2. To reduce noise and ensure that the signal is not distorted, shielded wires should be used for the signal input terminal connection wire and the double potentiometer connection wire.
3. Shell
(1) The input terminal, volume adjustment terminal, indicator light, and switch are fixed on the front panel; the output terminal, fuse, and power line are fixed on the rear panel.
(2) When drilling, the shell should be aligned with the circuit board.
The assembled amplifier is shown in the figure below.

4. Common problems and solutions in debugging loudspeakers

(1) No sound: The power is not connected; the DC regulated power supply is not working; the circuit connection is wrong.

(2) Loud noise: Not using shielded wire.

By making and debugging the amplifier circuit, the following ability goals were achieved:
(1) Able to correctly identify, detect and select components such as resistors, capacitors, diodes, transistors, integrated three-terminal regulators, integrated operational amplifiers, and integrated power amplifiers.
(2) Able to read practical electronic circuit schematics.
(3) Able to solder practical circuits according to circuit schematics.
(4) Skilled in using electronic measuring instruments such as multimeters, signal generators, analog oscilloscopes, etc. to test basic circuit parameters.
(5) Able to debug the completed circuit to meet design requirements.