A simple and portable audio digital to analogue converter with amplifying abilities.
The Texas Instruments PCM2707 serves as the USB interface. This interface provides a clock and I2S signal for the main Hifi digital to analogue converter, the PCM1794A.
Since this converter needs a 3.3V power source a LP5907 ultra-low-noise LDO is being used to generate the desired voltage.
The DAC provides a differential output current. This is being feeded into a two opamps that are used as transimpedance amplifiers which convert the DAC output current into a differential voltage. Then a difference amplifier converts this differential voltage to single-ended. For this the TI reference design TIDU672C was used. Therefore the Amplifier stage consists as two OPA1612 and a OPA1622.
A LM2662M switched capacitor voltage converter generates the necessary -5V to supply the operational amplifiers with +-5V.
The project is realized with the open source EDA tool KiCad.
With the current parts the whole project costs around 45€ at Digikey. For details have a look at the BOM.csv or BOM.html.
PCM2707 USB Interface
PCM1794A 24-Bit, 192-kHz audio DAC
LP5907 Low-noise LDO
LM2662M Voltage converter
OPA1612 Operational amplifier
OPA1622 Operational amplifier
Note: old design!