TDA7297 - Performance as needed at a very attractive price.
Key specs: 6.5-18V supply, 2x13 Watt in 8 Ohm, 0.1% THD, 50mA quiescent current.
DC offset measured at outputs: 13mV / 48mV (12V supply).
TDA7297 is the basic class AB amplifier chip that offers what is needed at a very attractive price. It is intended for use in vehicle audio equipment but may also be used for other low power purposes. A THD of 0.1% satisfies anyone but audiophiles. 2X13 Watt output power is sufficient for daily use. With a few peripheral components, a moderate size heat-sink and a single supply voltage source an amplifier can quickly be made.
In order to try what is available for around 1 Euro (without power supply), a DIY kit was bought and assembled as supplied, with a small heat-sink found on stock. The kit costs under 1 Euro and includes nevertheless a small single-sided fiberglass PCB. The components supplied were nothing but standard quality and the power supply line decoupling capacitor relies on energy storage in the power supply. Replacement with better components would have been possible but counter to the aim of investigating how cheap a reasonable power amplifier can be made.
The kit was quickly put together and connected to a 12V power supply with 10000uF of storage capacitance at the power supply output. It straight away worked without obvious flaws. Then the supply voltage was increased to 16V, still with the 10000uF storage capacitance at the supply output. The small amplifier board continued to function well.
The sound is pleasant and without obvious distortion. No important hiss. Good handling of the bass. It is the type of sound found with ordinary commercial audio products. Sufficient, but not a miracle in itself. Only when the price is taken into account the amplifier is almost a small miracle. It is a chip that is frequently found in commercial products because it is sufficient for most use and very cheap. A THD of 0.1% is absolutely decent and would have been fine two decades ago.
The small heat-sink used becomes somewhat warm but not unpleasantly hot. The heat-sink may be replaced with a more cooling-efficient aluminum plate or profile recovered from other use. Not much is needed.
Today more alternatives to the TDA7297 exist. Many of those are likewise offered at an attractive price although not as cheap as the TDA7297. For most DIY enthusiasts it is better to start out with a slightly better chip when constructing an amplifier. Some of these alternative chips offer an upper supply voltage range that exceeds that of TDA7297 and accordingly a higher output power. Other provide the possibility of operating with low impedance loudspeakers such that the output power is increased when using the same supply voltage. Almost all offer even better THD performance because they are more modern designs. Even audiophile chips exist for operation within the same supply voltage range as TDA7297. The choice is yours.
The small TDA7297 board we used is ideal for young DIY beginners because it is possible, for very little money, to build an amplifier that can serve in daily use and replace commercial products. It is supplied with various protection facilitates such that it is rugged in use. The wide supply voltage range allows for various supply sources, even batteries, to be used.
Comparative tests have not yet been performed.
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