Dev_LOOP-analog IO for DSP boards

[free electron]

Although this device is purely analogue, i'm posting the project here, because the main purpose is to use it as an analog IO board together with any kind of DSP dev board.
Such boards usually don't have proper HiZ inputs, mixing stages (analog dry path), input/output level adjustments and other features that are generally needed in the final design.
So here it is:

Dev_LOOP



a versatile stereo Hi input Z preamp / effect loop

Design goals:

• Mono/stereo operation with versatile IO routing
  
• High input impedance: 1MOhm
  
• Adjustable input gain: -/+15dB
  
• The mixer stage can work as Dry/Wet blender or as typical Effect Level control (for delays etc.)
  
• Output level control
  
• Low impedance outputs
  
• Standard 9VDC power requirement
  

The main purpose is to use this device to prepare the guitar or any other signal to be sent to some kind of stereo DSP development board, like the FV1, audio shields, codecs etc., get the signal back, add more analog anti alias filtering and mix it with the non processed Dry signal.

The input and output jacks allow to use a few routing scenarios:

• typical Left/mono input, Left signal is sent to both input channels
  
• separate mono TS jacks for Left and Right input channels
  
• stereo TRS jack carrying both input channels
  
• Left and Right output channels summed and available on the Left Out
  
• separate mono TS jacks for Left and Right output channels
  
• stereo TRS jack carrying both output channels
  
• additional test points on the PCB for easy scoping
  
• input/output jack presence "sense" signals available on pin headers
  

The construction is mostly SMT, parts are in 0805 size, SOIC14 for the quad opamps. The Pots are ALPHA 11mm stereo PCB mount ones. I have used the stacked Cliff jacks to save the board space. The board is two layer, not really suitable for home etching (unless you are good at drilling lots of 0.3mm holes, not to mention plating them through). All design files, including schematic and gerbers are available in the github repository, which i'll be linking down below. The design is verified and works.



Schematic (click to open larger file):



Github repository with all design files:

Dev_LOOP project files

I ordered a small batch of the pcbs, will keep 2-3 for myself. Still have a few left. PM me if you want to get one. Alternatively, you could use the gerbers to order your own copy. The size is 5x10cm.



Hope you like it! Enjoy!

Piotr

[thelonious]

Thanks for sharing!!