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    September 2nd, 2016

    The implementation of Alex Nikitin attenuator ( http://www.ant-audio.co.uk/ )

    Working on the GUI side:
    Based on Arduino, takes Apple's IR remote commands and displays the attenuation level on 20x4 LCD screen.
    It hella clicks! Yet,
     - No clicking is heard in speakers (some "advanced" two-stage relay switching)
     - Goes to max attenuation during power-on (in hardware, before Arduino boots-up - so no power-on "thump").
     - Keeps the attenuation when powered-off (no power-off "thump")
     - No measurable "clicks" are passed from control circuitry to analog side as long as there is no audio signal present.
     - Measurable "clicks" due to relay contact noise during switching. Yet, i can't hear them in normal application when connected to amplifier.

    PCBs arrived:

    Schematics: ra02_release_1.pdf

    Last (?) version: (meow)

    First (?) version:

    Schematics (component values are incorrect).

     - 64 steps, -64dB attenuation range with 1dB/step or -128dB with 2dB/step.
     - Use of precision MELF resistors (thin film).
     - Latching relays - no power required, less noise crosstalk from the digital side.
     - Serial input with shift-registers, ULN-buffered relay drivers, on-board PSU to keep the relay's supply noise low.

    By s3t © 2011