Amplifier
Initially Peppy Player was using HiFiBerry Amp+ amplifier. It had the drawback - it didn't support the sample rate 22,050 Hz which is used in many audiobooks. HiFiBerry produced new amplifier Amp2 which doesn't have such drawback. Therefore Amp+ was replaced by Amp2 in Peppy Player. I'm not sure that you can buy Amp+ now that's why only the description of the Amp2 will be presented below.
HiFiBerry Amp2 is the integrated amplifier module. That means that instead of using traditional components for a digital audio system: DAC - Pre-Amp - Power-Amp you can use just one - Amp2. It has Class-D amplifier on board which provides high quality output on 4-8 Ohm speakers. As any other Class-D amplifier it's also very efficient meaning that there is no need to use heat sink or fan.
Raspberry Pi feeds digital audio data to Amp2 via I2S (Integrated Interchip Sound) signal. It comes from Raspberry Pi to Amp2 through GPIO connector. This is the same signal which you can find in traditional CD players between the transport and DAC.
Amp2 is ready-to-use right out of the box. You just have to install optional spacers (either your own or those which come with Amp2) on Raspberry Pi.
Amp2 has 40-pin connector with pins which protrude through the board and allow to connect any other devices which need GPIO signals. Peppy player leverages that connector on Amp2 to connect another external hardware components: IR Sensor, Rotary Encoders and Touchscreen. Just remember that pins used by Amp2 should not be used by any other component.
After attaching Amp2 to GPIO connector on Raspberry Pi some software configuration should be done to make Amp2 work properly. The details of that process will be covered in the separate chapter.