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

[Tim Ressel]

Because clipping sucks!

There are two factors that go into op amp headroom: rail voltage, and the output swing of the amp. Older amps like the TL082 could only swing to within 1.5 volts of the rail, and that is a typical rating. The minimum rating is 3 volts from the rail. And that's with a 10K load. Newer amps, like my current favorite LME49723, can get within 0.9 volts at 10K load and 1 volt at 2K load. And it can drive 600 ohms. 

Tim Ressel
Circuit Abbey
503-750-9331
timr at circuitabbey.com




________________________________
From: Justin Owen <juzowen at gmail.com>
To: SDIY List <synth-diy at dropmix.xs4all.nl> 
Sent: Tuesday, March 10, 2015 11:21 AM
Subject: [sdiy] [Slightly OT] Op-amp headroom in synth & audio applications


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




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