Here is the Arduino code and PCB layout files to build a high fidelity preamplifier. It has the following features:
- A precision volume control using a R2R multiplying DAC
- 6 input selector with mute
- Volume and input control via rotary encoders and infrared remote.
- Start-up mute.
Based on a design from a Analog Devices circuit note: http://www.analog.com/en/design-center/reference-designs/hardware-reference-design/circuits-from-the-lab/CN0025.html
This design is also used by a number manufacturers.
- 65536 linear steps (16bit)
- Any gain possible, set by OPAMP and resistors
- Excellent performance
- Can drive headphones
- Compact
- SPI controlled
- 6x inputs
- Mute for the output
- SPI controlled using a MCP23S17
- Latching relays so no constant current draw (mute is not latching, obviously)
- Uses high quality Panasonic GQ relays (AGQ)
Designed for CMC 816 RCA sockets, they can be soldered directly on to the PCB and are easy to find on eBay or Aliexpress etc.
The IRremote library is from here: https://github.com/z3t0/Arduino-IRremote