Preamp Two

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.

Hardware

MDAC attenuator

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

Input selector

• 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)

RCA board

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.

Infrared remote control

The IRremote library is from here: https://github.com/z3t0/Arduino-IRremote