USB 2.0 Multichannel DAC Project
This project is in the very early design stages. I'm currently looking around which chips to use...
- Must offer USB 2.0 high speed compliant audio device so no driver is needed under linux
- Sample rates above 48kHz must be possible, ideally 192kHz and 24bit sample depth would be very desireable.
- Multichannel design. For the moment i need at least 4 output channels but the board should easily be upgradeable to 6 or 8 channels
- As USB synchronous transfer mode is prone to jitter a resampling DAC chip with a very good PLL is required as well as a low-noise DAC clock oscillator.
- Low noise external power supply should be considered as USB bus power will always be pretty dirty. Maybe powering the USB->I2S converter with USB bus power is a good idea though as we will spare some components and can completely isolate these power rails.
- A fine-grained software wolume control is mandatory. Possibly by adding a second usb port for remote control options or a esp8266 daughter board that can send I2C control signals to the DACs and operate as a webserver to receive volume control commands?
|Price||0,00€ (Samples!)||?||~90 US$|
|Module Price||~25 US$||~22 US$||not sensible, want to use all 8 channels then|
|Output (I/V)||Voltage||Voltage||Voltage, better in current mode|
There are currently three USB to I2S solutions that are in the race:
- The C-Media CM6631A (2+2 I2S putputs) and CM6632A (8+2x I2S outputs). The first on would be suitable for now as i only need 4 channels at the moment. The second one would be more future proof but no modules are available on eBay or aliexpress.
- XMOS X200 class of chips. unfortunately these are not in any way sound specific chips but only fast microcontrollers with lots of IO and a USB 2.0 compliant PHY. Would require a lot of development.
- The Amanero USB to I2S solution uses an ATMEL microcontroller and a CPLD to. Pros: Maybe firmware available! Cons: Only 2 channel I2S at the moment.