[ben1040]

Reminds me of an electric organ a friend had. It was totally analog and dated back to the 60s or 70s.

The volume control knob abruptly stopped working; the organ was stuck at maximum volume.

He opens it up to discover the volume control simply controls the brightness of a light bulb, which had burned out.

The light bulb shone on a photo resistor, which governed the output volume.

[theoh]

Faders in DJ equipment are often optical -- apparently a potentiometer would be noisy.

http://djtechtools.com/2011/11/01/fader-technology-a-primer/

[jsmthrowaway]

That would make DJ gear the exception, then. There are slide pots for that purpose which do quite well with audio across them, they’re just in bigger mixers for sound reinforcement and radio gear. Digital obviously negated needing them to work the same way — it actually rearchitected how an entire mixer works — but analog pots got very good toward the end of their “run”. Lots of quality radio gear out there with beautiful 10Ks, much still in use. I wouldn’t call it “old” like that article does. Then again, DJs also beat the shit out of faders when they work, so it might be a good idea from a reliability perspective.

Coming from the reinforcement side, a lot of DJ gear baffles me. They look at audio much differently, which I suppose is understandable when you’re mixing two decks with an occasional bandpass versus a 50+ channel metal band with subgroups and racks of outboard effects.

[dharma1]

Same reason some guitar wah pedals use optical control. There are ones with mechanical pots but you have to keep replacing the pots every couple of years when they become "scratchy" as you move the pot back and forth quite a lot in use

[jsmthrowaway]

Yep. Definitely maintenance involved and a culture of care and feeding of faders on high-end gear.

[Bromskloss]

> Digital obviously negated needing them to work the same way

So, how do faders and knobs work nowadays?

Oh, are they perhaps still potentiometers, with the difference that you can now low-pass filter them before reading off and digitising their values, since you don't have to pass the audio signal through them?

[rzzzt]

Some knobs use rotary encoders. A nice side-effect is that they are "infinite" in either direction, unlike helical or single-turn pots.

[zkms]

Yeah, I have vague recollections of taking apart an analog electric organ (like https://en.wikipedia.org/wiki/Hammond_organ) and seeing an "optocoupler" with an incandescent bulb and an LDR in a little enclosure.