headphone-dac-with-amp

Portable headphone DAC with amplifier stage

A simple and portable audio digital to analogue converter with amplifying abilities.

Structure

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.

Datasheets of used components

PCM2707 USB Interface

PCM1794A 24-Bit, 192-kHz audio DAC

LP5907 Low-noise LDO

LM2662M Voltage converter

OPA1612 Operational amplifier

OPA1622 Operational amplifier

Rendered picture of the current PCB layout

Note: old design!