how do you decide how much power to supply to an op amp?

[ode2no1]

if you were designing a circuit and the op amp is rated up to 17v, how do you decide how much power to give it?i know pedals are usually 9v, but what determines the voltage in a circuit where you planned on running the thing on it's own dedicated power supply at all times? and what determines whether you want to do ac or dc?

[newfish]

I guess one factor would be how you intend to power the device in the real world.

Multiple wall-warts in a stage-rig can be a pain in the behind.

The 'standard' 9v supply is / was originally easy to obtain when these standards were being established.

Assuming you're using electro caps of at least 16v (35v would be better), there's no real reason why you shouldn't go for 15v supply or whatever, assumng that the 17v is not the *absolutely screwing this device to its limits* supply voltage.

Running *anything* at its limits will reduce its useable life. 

Supplying more voltage to an amplifier will give you more headroom - and the device should go into clipping much later than it would with a lower supply - so it's cleaner for longer.

Cheers!

[Processaurus]

Yes, when you can have high power supply rails you might as well make them high.  Professional audio and synth stuff, where the power supply is the choice of the designer, traditionally runs opamps off +/-15v, for supreme headroom, even with a good amount of gain at different points in the circuit.  If you're making something with an internal power supply, and you just have to pick a number for the voltage, I can't think of a reason not to use +/-15v rails, though you may never take full advantage of the voltage swing you can produce. 

In datasheets for analog and logic IC's that can take a variety of power supply voltages, it will have figures for how the chip's performance differs at those voltages (often they'll show specs for running at 5v, 10v, 15v).

In 9v pedal circuits where headroom is an issue and you need big signals to remain clean and unclipped for whatever reason, it can be handy to use a charge pump (like the LT1054) to generate a -9v supply and run the opamps off of the +/-9v for about 18v of swing.  That being said a regular guitar signal is about 400mV peak to peak, so 9v is usually adequate for processing guitar signals.