The device provides the maximum gain of 45 dB. However, it can be lowered by placing an external RC series circuit between the feedback pin (6 and 11, see pin diagram) and ground. The datasheet recommends not to reduce the gain under 36 dB. In order to get the maximum gain, use R=0 and C=100 µF (as shown in the application circuit above) between the feedback and ground.
The low cut-off frequency (fL) of the output signal depends upon the load resistance (speaker, RL) and the output capacitor 470 µF. If the speaker resistance is 4Ω, the low cut-off frequency will be,
fL = 1/(2π CRL) = 80 Hz
An interesting characteristic of TEA2025 is it has built-in thermal protection circuit. If you want to run it at its full capacity (5 W), you should provide a heat sink in the circuit. In case you don’t, the internal thermal protection won’t let the device damage; all that happens is that the output power is reduced when an excessive junction temperature is sensed.
At the input stage, a logarithmic dual taper potentiometer (10 or 20 K) can be used to provide the volume control feature. The 0.22 µF capacitors at the input side help to minimize any noise due to variable resistor contact. The 0.15 µF capacitors at the output end are for frequency stability. Use of other value capacitors could result in unwanted oscillations at the output. Long wire connections and ground loops in the circuit could also cause oscillations, so a good layout of the circuit PCB is very important.
I built this circuit on a 5 cm x 9 cm general purpose prototyping circuit board as shown below. The circuit is put inside a 6 cm x 11 cm size plastic enclosure and necessary connections (power supply, speaker, and stereo input terminals) are drawn out of the box. The circuit can be powered from 3-12 V power supply. I am powering this with my spare 9.6 V rechargeable battery from my broken RC toy. I am happy with the performance of TEA2025 as an stereo audio amplifier.
