Hello Friends,

I'm now posting regarding my Teensy 4.0 PCM1865 Audio Shield. This is part of a larger project to create a many input, many output digital mixer. But I believe the cards could be very useful for many of the projects I'm seeing posted here on the Teensy forum. My PCM5242 DAC card is currently being built at the fab house, and this one will go to fab shortly. If you have any feedback, please feel free to chime in.

This board features a PCM1865 with 4 ADC channels @ 110-dB SNR, and a front end that incorporates a preamp that provides 12 dB to +32 dB of gain. Each input channel can have either a balanced or single ended input. It's another "lean and mean" design that is supposed to be small and efficient.

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The board exposes pins for connections to your "IO Board". I know that some users don't like this but for my project this is imperative. It makes it much more flexible. The boards will stack on top of eachother to provide the shortest possible distance for the Clock signals to travel to each card. Two of these cards stacked up create 8 inputs, and with all the I2S data lines on the T4 there is a theoretical input of many... Then the Analog Inputs are exposed to headers that will lead to the input boards. These input boards will be mounted to the chassis - so having them separated from the boards makes it easier to put them where they make sense physically outside of the case while the actual device doesn't take up much space. These input boards can have pretty much any input jack you want. Here is one example that provides 2 single ended RCA inputs and 2 Combo Jack inputs...

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Possible input boards include 3.5mm, XLR, 1/4 inch, RCA, and pretty much any other input type you prefer for your project. The PCM1865 has 8 input lines that can also be selectable. So technically you could have up to 8 single ended inputs - on 4 ADCs. This would be useful for someone looking to MUX or MIX inputs. In the use-case above I'm using 2 single ended, and 2 balanced lines. This gives me a simple "aux in" and 2 balanced microphone inputs. The type of equipment I'm using in this project are powered speakers, dynamic microphones, CD-players, etc.

Resources:
PCM1865 Datasheet - http://www.ti.com/lit/ds/symlink/pcm1865.pdf
Teensy 4.0 PCM5242 Audio Shield Forum Post - https://forum.pjrc.com/threads/60386...ded-DAC-Module
Teensy 4.0 Audio Toolkit Shield - https://forum.pjrc.com/threads/60411...oject-in-Kicad

Schematic
TEENSY4_PCM1865_AUDIO_SHIELD_Schematic.pdf

Questions:
- I just realized that some people will want phantom inputs. I might be able to expose some header pins to provide that functionality (on a second board). Before going to fab, I might research that just a bit to see how that would fit. Any input is appreciated. It might be possible to daisy chain a phantom insertion after the inputs of this card... I will study up on this and report back.
- I have spent a lot of time making sure my input filters are correct. But a second set of eyes on the input filters would be appreciated.