Description
My television has only a single mono loudspeaker, so I have built the following small audio amplifier to connect better loudspeakers. The amplification is done with 2× TDA7240 ICs from SGS Thomson. This IC is designed for car radio applications. But this simplifies the power supply design, because only one 12V voltage is needed instead of an additional negative voltage.
The datasheet says that the amplifier ics can deliver 20 watts into 4Ω-Loudspeakers and 12 watt into 8Ω-Loudspeakers. I do not know if my construction can reach this values but I think it is good enough for watching TV.
The circuit is quite simple and built according to the proposal in the datasheet, merely for 2 channels and without the mute switch, because this can be done with the TV. The power supply of this amplifier is a conventional one with a 50VA 12V toroidal transformer, bridge rectifier and two 4700µF electrolytic caps.
Only a few additional components are needed for the amplifier, so the whole circuit fits on a 3,5cm × 5cm PCB . But the PCB is not the only component needing space inside the amplifiers case - the ics need an adequately sized heatsink. They will not be destroyed when the heatsink is too small because they are protected against overheating and short-circuit.
The presented amplifier cannot compete with real hifi amplifiers but in my opinion it is really good to watch TV and a great improvement in opposite to the TVs' mono output.
The stereo potentiometer I used has some problems because the two resistors have not exactly the same value. So I already think about a digital volume and sound control (treble, bass, balance), perhaps with a remote control. If I have some news about that I will publish it on this website.
The case
The case of this amplifier is made out of 8mm poplar plywood (hope this translation is correct ...) I can only recommend this material for building such cases. But you should paint it with lacquer to get a hard and shiny surface. And remember to make enough holes into the bottom and cover of the case to avoid overheating of the amplifier.
Warning: The power supply of this amplifier is connected to the mains. Household electrical current is extremely dangerous, and it may be illegal for you to perform your own wiring, even for equipment that connects via a standard wall outlet. If you are unsure of the procedures, terminology or anything else that may cause a potentially fatal error due to oversight or lack of knowledge, you must seek assistance from a qualified electrician. Remember that if someone is killed or injured as a result of your work, you may be held liable and subject to severe criminal and financial penalties.
Pictures
Downloads
Eagle-Projekt: audioamp-20040827.zip
Links
- Elliott Sound Products: Basics, theory and circuits for do-it-yourself audio, great site!
- SGS Thomson: Manufacturer of the amplifier ics.
- TDA7240: Datasheet of the TDA7240.
