[sdiy] [Slightly OT] Op-amp headroom in synth & audio applications

[Justin Owen]

Hope nobody minds these couple of slightly OT posts - just know I'll get a good answer here!

I've been wondering about power supplies vs. output signals on different formats and it seems there's a lot of 'spare' headroom...

MOTM: +/-15V supply  w/- audio output of +/-10V (20V PP) i.e. output is 67% of supply

System 500: +/-16V w/- peak transients at approx. +18dBu or approx. +/-8.7 (17.4 V PP)  i.e. output is 54% of supply

Eurorack: +/12V supply w- with audio output of +/-5V (10V PP) =  i.e. output is 42% of supply!

I understand that there's a margin for staying away from the rails and for the tolerances of parts like VRegs and what not and maybe part of it is a hangover from the days of less efficient amps - but considering that a good op-amp like the OPA134 will (according to the data sheet) operate down to +/-2.5V and work-horse amps like the TL072 aren't far behind that - why so much headroom?

Just curious - thanks,

- J