Highest acceptable mA draw with 9v battery?

[B Tremblay]

Above what level of current draw is considered "too much" for economical use with 9v battery?

What about six AA in series, providing 9v?

[Mark Hammer]

I've heard it said that anything more than 15ma starts to make 9v battery lifespan short enough to be a nuisance and financial drain.

For miniamps (i.e., practice amps) you need to be cogniscent of the "idling" current (quiescent current) of the power-amp chip in question.  Some chips draw more current than others even when you're not playing, and even though they may not draw more current when playing.  In some respects it's the quiescent current that is the real killer.

I have an NJM2073-based practice amp I made that seems to enjoy 9v battery life well in excess of what I've experienced with LM386's, or at least it seems that way.

[cd]

Keep in mind that most 9V alkalines are rated for around 550mAH (down to 0.8V), and most carbons are around 250mAH.  A pedal that draws 15mA will be useless (or in the "dying battery" sweet spot) after 20 hours with an alkaline, or half that with a carbon.

[B Tremblay]

Coincidentally, recent experiments with low power amp ICs (including the JRC2073) prompted my query!  I've been measuring the current draw and checking my figures against the datasheets, but didn't know if those numbers were outside the realm of battery viability.

Thank you for the quick and helpful response!

[gez]

I love low-power amps.  A lot don't have any/much audible effect on a circuit (and when they do it's sometimes better).  I'm always amazed when doing comparisons with ordinary chips what a difference they can make;  I subbed in a quad chip in a state variable filter circuit once and the total current consumption plummeted to just 1ma!  

[cd]

Oh yeah, six AAs in series is a good idea - if you get the NiMH rechargeable AAs that are 2850mAH, that's six times longer than a square 9V!