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USB DAC with amplifier

A USB DAC with a 3-W x 2 amplifier

andreas-dahlbergAndreas Dahlberg
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This is a prototype for a USB DAC with an amplifier. When plugged into a USB port the OS recognizes it as a USB sound card and no installation of drivers is need. The amplifier is capable of driving two 3 W, 8 Ohm speakers.

A SPI interface can be used to control playback on the connected computer.

USB Interface

The USB interface is all done by the PCM2705 IC. When the DAC is connected to a computer it recognizes it as a USB sound card and no manual installation of drivers is need. The DAC can control playback on the computer with the following HID-states:

  • Mute
  • Volume up
  • Volume down
  • Play/Pause
  • Stop
  • Previous
  • Next

DAC

The DAC used is the one integrated into the PCM2705, it is a 16-Bit Delta-Sigma Stereo DAC with a SNR at 98 dB. Many similar boards use an external DAC for better performance but since small size and cost is more importent in this project i choose the integrated DAC.

Amplifier

The amplifier used for this project is TPA2008D2 from TI. It is a 3-W Stereo Class-D amp.

SPI interface

PCM2705 has a SPI interface that can be used to set the HID-states. I wrote a small Arduino library so playback can easily be controlled from an Arduino.

  • 1 × PCM2075 Stereo USB DAC with line-out
  • 1 × TPA2008D2 3-W stereo class-D audio amplifier
  • 1 × Crystal 12.000 MHz HC-49/S 30 pF
  • 1 × Resistor, 1MOhm 5% Metal film
  • 2 × Capacitor, 15pF 10% Ceramic

View all 21 components

  • Android and USB DAC

    Andreas Dahlberg • 01/06/2015 at 21:52 • 0 comments

    Found out today that support for USB audio peripherals was added in Android Lollipop. Tested the USB DAC with my Nexus 5 and it worked perfectly! The only downside is that a external power supply is needed when volume is increased.

    Android USB Audio

  • New DAC/AMP is done!

    Andreas Dahlberg • 04/14/2014 at 15:19 • 0 comments

    I just finished soldering the components on the latest PCB. Did some testing and everything seems to work. Had some problems with the volume at first, it would change randomly when i got close to the PCB. I think a bad ground connection caused this. The USB-cable i used was very loose in the connector and when i changed the cable everything was fine.


  • Components and PCB arrived!

    Andreas Dahlberg • 04/07/2014 at 16:33 • 0 comments

    Got the new PCB and some missing components for the new version today! Unfortunately i could only solder the USB connector before my almost new solder station broke, so now i must get a replacement before i can continue. 


    Here is the new PCB compared to the old one.


  • PCB ordered

    Andreas Dahlberg • 03/24/2014 at 12:05 • 0 comments

    The PCBs are now ordered from OSH park :)

  • New PCB layout

    Andreas Dahlberg • 03/20/2014 at 13:20 • 0 comments

    The new PCB layout is soon ready :) Only some routing and adjustments left


  • Updated schematic

    Andreas Dahlberg • 03/15/2014 at 16:57 • 0 comments

    I am almost done with the new schematic for the (hopefully) final version. The only thing left before i start with the PCB layout is to check all footprints and recheck all connections.

View all 6 project logs

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Discussions

Anthony wrote 04/13/2017 at 02:38 • point

Did you hand solder the thermal pad on the amp? If so, how did you go about it? 

  Are you sure? yes | no

Andreas Dahlberg wrote 04/18/2017 at 19:28 • point

Yes i did. It does not show in the pictures but the thermal pad is also exposed on the bottom side of the PCB. So i put some solder on the top side pad, put the IC on and applied heat on the bottom side.

  Are you sure? yes | no

Eric Evenchick wrote 04/07/2014 at 20:31 • point
Neat, the PCM2705C looks like a really cool part... all in one USB DAC that just works with Windows.

Any chance you could put a PDF of the schematics in the Github repo? It'd be nice to see them without needing a CAD tool. Thanks!

  Are you sure? yes | no

Andreas Dahlberg wrote 04/08/2014 at 08:09 • point
Yes, really nice that no special drivers is needed. I just uploaded the schematics to the Github repo as a PNG file, hope it works!

  Are you sure? yes | no

Eric Evenchick wrote 04/08/2014 at 17:50 • point
Awesome, thanks! It's actually not too many components. Nice to see a mostly through hole design for this.

  Are you sure? yes | no

AVR wrote 03/27/2014 at 02:04 • point
This is pretty cool! I'm thinking about making something similar when I'm done with my current projects. I'm working on an audio board right now that I might be able to use to make a USB DAC like this minus the amp though.

  Are you sure? yes | no

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