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:


Release!
Schematics: ra02_release_1.pdf

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Last (?) version: (meow)

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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.