TDA7850 2.1-Channel Class-AB Amplifier Board 2×80W+120W Subwoofer Amplifier Module DC9-18V for Car/Desktop Audio DIY

TDA7850 2.1-Channel Class-AB Amplifier Board Product Overview

This is a 2.1-channel Class-AB analog amplifier board built around the STMicroelectronics TDA7850. With a DC 18V supply, it delivers a nominal 80W per channel into 4Ω for left and right, plus 120W into a 2Ω subwoofer load. The module accepts DC 9V to 18V, offers both 3.5mm and 3P-2.54mm audio inputs, supports 2Ω to 8Ω speaker loads, and includes reverse-polarity, short-circuit, thermal, and over-current protection. The TDA7850 is a MOSFET-output Class-AB power IC designed by ST for high-power car audio, featuring rail-to-rail output swing and strong low-impedance driving at low supply voltages.

Typical Applications

Car audio upgrades and trunk subwoofer systems

Desktop 2.1 multimedia audio and PC speaker upgrades

DIY active subwoofers and 2.1-channel amplifier builds

Portable high-power audio and outdoor sound reinforcement

TV audio external bass enhancement systems

Motorcycle/e-bike audio upgrades

FAQ

Q: How is the 2×80W + 120W rating achieved?
A: The TDA7850 is a four-channel BTL amplifier, with each channel capable of up to approximately 80W into a 2Ω load. The board uses two channels for left/right (2×80W nominal) and parallels the other two for the bass channel (120W nominal). Actual continuous power depends on supply voltage, load impedance, and thermal conditions; the nominal ratings typically correspond to 2Ω loads at higher supply voltages.

Q: What power supply does this board require?
A: Use a power supply with sufficient current capability—at 12V, rated current should be at least 10A, preferably 15A or higher to prevent voltage sag during peak output that could trigger protection or shutdown. DC9-18V all work, but higher voltage yields more output power and demands better cooling.

Q: Class-AB generates significant heat—what thermal precautions are needed?
A: The TDA7850 dissipates considerable heat at high power. Ensure the heatsink makes tight contact with the chip's metal tab and that the enclosure has airflow. This board includes a large aluminum heatsink, but for 2Ω loads or extended high-volume operation, adding a fan or ensuring a well-ventilated installation is recommended. The chip auto-protects on over-temperature, but frequent protection indicates the thermal design needs improvement.

Q: How is the bass channel derived from the four BTL outputs?
A: Each TDA7850 output is already an internal BTL bridge and cannot be externally bridged further. 2.1 boards typically parallel two outputs (Paralleled BTL) to drive the subwoofer for greater current capability, rather than simply "bridging two channels." This increases bass-channel drive power without altering the chip's internal topology.

Q: How are the audio source and speakers connected?
A: Audio input is via the onboard 3P terminal or AUX, supporting single-ended audio signals. Output uses screw terminals for left, right, and bass channels; speaker impedance should match within 2-8Ω. Verify power polarity before power-up—onboard reverse protection reduces risk, but correct wiring remains essential.

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