I just chucked this thing together just for fun to see what a power supply regulator ic would do if it was made to process audio instead of ripple and noise. (Not much different from some people's music. Anyhoo...) The LM317 has a ripple reduction of 80dB to 10kHz and then slopes gently downhill from there so what we have is basically a class A power amp on a chip. In the cct the top ic is a voltage follower and the bottom one is a constant current sink. My generator would only produce 15v p/p so that's all I tested it too but it should swing to within 2 volts of either rail. The whole thing is super linear. Frequency response is to 100kHz then the 100r and 560pF start to roll it off. Without these it wasn't stable producing a square wave. Standing current is set by the 2R2 resistor right at the bottom - it always has 1.2 volts across it so the current is according to that. I havent yet run a speaker or headphones off it (reactive load) but it will be interesting to see. Component values are not really optimised, e.g. the 10k voltage divider should really be that which gives a dc output voltage exactly half supply. On a square wave the rise and fall times are 1.1 uS with absolutely no overshoot. I used ST brand regs, I don't know how other people's would go. This has gotta be the most under-rated chip ever!
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