Low-power active speakers designed with TDA2822M

TDA2822M is a very classic and excellent audio power amplifier integrated circuit. In the early 1990s, it was widely used in portable radio recorders by domestic and foreign home appliance manufacturers. TDA2822M can also be often seen in some higher-powered Walkmans, especially those with built-in speakers.

TDA2822M is a two-channel audio power amplifier integrated circuit developed for portable recording and playback equipment. It has the characteristics of low crossover distortion and low quiescent current, and can work in two-channel stereo or mono bridge-type amplifier (BTL) mode. TDA2822M has a wide operating voltage range and can work normally within the range of 1.8V-15V.

The nominal output power of TDA2822M (1KHz, 8Ω, 9V, 10% total distortion) can reach 1W in stereo mode and 2W in bridge mode.

Other technical indicators of TDA2822M are as follows:

Maximum peak current (PeakOutputCurrent): 1A;

Quiescent Drain Current: ≤9mAVCC=3V);

Total harmonic distortion (1kHz, 8Ω～32Ω, typical value): 0.2%;

Closed-loop gain (typical): 39dB;

Channel imbalance (stereo state, maximum value): ±1dB!

Channel separation (1kHz, stereo state, typical value): 50dB;

Input impedance (1kHz, minimum): 100kΩ;

Load range: ≥4Ω.

TDA2822M is cheap, but it is best to buy the one starting with TDA, preferably the original STMicroelectronics. Do not buy the one starting with D, and do not buy TDA2822 (that is, without "M" at the end). The former has poor sound quality, and the latter has a narrow supply voltage range. It is rare to find DIP16 package, and the sound quality has not been commented on.

In actual production, the bridge connection method is often used, which can save two output capacitors that are easy to affect the sound quality. Figure 1 is a circuit diagram of a channel. In actual production, two sets of such circuits are required. TDA2822M can work in direct coupling mode, provided that the input signal cannot have a DC component, otherwise a coupling capacitor should be added to the input end of the sound source.

When you power on for the first time, do not connect the speaker. Use a multimeter to measure the output terminal (between pin 1 and pin 3). If it is at the millivolt level, you can use it without worry. Otherwise, it is best to connect a 1uF high-quality capacitor, such as a CBB capacitor, to the input terminal (pin 7). Of course, an electrolytic capacitor is also OK. When measuring, pay attention to the multimeter's gear should be adjusted from large to small, do not put it in the lowest gear at once to avoid burning the instrument.

The amplifier shown in Figure 1 is for MP3 players, so the input resistor for pin 7 is 820Ω instead of the typical 10kΩ, because the output load of an MP3 player is generally a 32Ω headphone. Although using a 32Ω resistor may be better, the MP3 player will consume more power and it will be difficult for this amplifier to use other audio sources.

In actual production, you can directly use the experimental board, and it is better to use a printed circuit board if conditions permit. When using a homemade printed circuit board, since there are relatively few components, you do not need to drill holes, and the components can be directly soldered on the copper foil surface, which is the so-called "root welding". Shorten the pins of the resistor and capacitor components appropriately, and cut the bottom edge of the TDA2822M flush, and lay it flat for soldering.

If conditions permit, it is best to use a CBB capacitor for capacitor C2 at pin 5 in Figure 1 to improve the sound quality. In actual listening, you can try to remove resistors R2, R3 and capacitors C4, C5 at pins 1 and 3. If there is no difference in the listening experience and the amplifier does not self-excite, it is also acceptable. The intuitive way to judge is: when self-excited, the IC temperature is much higher in comparison.

Since the TDA2822M has a wide power supply range and excellent sound quality, this amplifier can be fully used as a computer multimedia amplifier, and its listening experience is no less than that of products costing one or two hundred yuan.

The whole circuit is powered by a separate transformer, and 6V to 9V can be used. Filtering and voltage stabilization can use common active filter circuits or three-terminal voltage regulators to improve the signal-to-noise ratio. Here we recommend a more distinctive one, as shown in Figure 2. The main difference between this circuit and the electronic filter circuit we usually see is that an inductor coil is added to the base of the transistor, so as to achieve the ideal filtering effect with a low-power, low-inductance inductor. This circuit can filter out the AC noise in the power frequency power supply very well.

VT1 in Figure 2 can also use medium-power tubes above 2A, such as 2SC3074, 2SD14092SD882. The capacitors C2 and C3 of the base of VT1 and VT2 use CBB capacitors of similar capacity, which will have a better effect. Inductor L1 can be made by yourself, using Φ0.15mm enameled wire to randomly wind 200 turns on a 100kΩ resistor. It can also be replaced by a winding on the middle circuit of a radio, or a color-coded inductor of more than 330uH can be used.