one of my hobbies is DIY audio. here is a headphone amp with a nixie volume control display!
its arduino based (uses my own arduino board called LCDuino). this time, no lcd, but nixies.
I was going to use an arduinix board (or 2) but decided to try making my own from perf for this proto build. I'm not muxing the nixies and so it didn't make sense to use the 'nix board (avoiding muxing was due, partly, to this being an audio system and I didn't want extra noise to come in that didn't need to be there). here's the underside of the board:
there are 4 nixies, driven by the customary russian 74141 chips via BCD, but to supply the 16 bits needed I used 2 8-bit port expanders (i2c), pcf8574. I use them in other projects and they were easy to apply here. the nixies sit on a board with the 74141 and 8574 chips. a small dc/dc converter was bought from ebay and is located in the chassis, away from the audio wiring.
there is a learning IR remote control and the volume knob is a motorized pot; if you use the IR remote to change volume, the pot moves
the volume control is a relay and resistor (r2r) attenuator we call the delta-1. it gives accurate half db steps from 0 down to -127.5db (shown on the display).
the amp tech is from AMB (called 'beta 22') and its an all discrete bipolar+fet+mosfet system. the power supply to the amp is also fully discrete and designed by AMB. (I designed the LCDuino and delta1).