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  • 28/02/2018

    The amplifier has differential (bridge) outputs so can provide approaching 10 volts peak-to-peak swing on a 5 volt supply. The data sheet for the XPT8871 (via Google search; in Chinese) claims 5 Watts into a 2Ω load and 3.5 Watts into 3Ω load. However graphs in the data sheet show more like 1.5 Watts (with 10% distortion). Note the chip is supposed to shut itself down if it gets too hot. The data sheet says it's compatible with the LM4871, for which a data sheet is available in English. However pin 3 of the XPT8871 controls mode (AB or D) whereas for the LM4871 it is a differential input. On the amplifier board, pin 3 is held low so the amplifier is class AB. The gain is about 62x (36dB). Unfortunately there is no provision for setting the gain with a feedback resistor to the chip's input. With my limited test equipment, the upper 3dB frequency of the amplifier board is surprisingly high, about 100kHz, but the lower 3dB frequency is about 350Hz: OK for speech but disappointing for music. Attached photo shows output with 500Hz square wave input. Note only one of the two pins labelled "IN" is the input; the one towards the supply connections is a second ground connection. The circuit diagram on the Banggood website is not the circuit of the amplifier board: it's taken from the XPT8871 data sheet. It's a little surprising that the board is not supplied with pin headers. Of course the amplifier board is amazing value from Banggood.

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  • 19/07/2018

    Came in odd packaging but the product came safely

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