the other advantage is with 2 9v batteries you can eleiminate the rail splitter and take ground from the midpoint between the batteries.
This can help overcome some of the limitations of using a railsplitter, and the high impedance problems using a buffer or resistor method.
Larger quantities of AAA or AA batteries is better... but if building a portable amp, this is not usually an option.
I always use 2x9V unless the particular enclosure absolutely could not fit 2x9V. I figure I can always shrink the amp even more to make 2x9V fit.
Not economical? Do they still sell single 9V packages? All I ever see is dual 9V packages at WalMart and the likes. Since you have to buy two anyway, might as well put them to use... of course you'll go through batteries twice as fast... but it is nto that bad really. Just buy some rechargeables- they look expensive when you pay $10 a piece... but think... 2x standard 9V are $4 or so... so after you replace a few times, the rechargeables have paid for themselves.
Also, as was pointed out above, if you want to opamp roll, 2x9V is a much better option because you can use pretty much any opamp. Also on this note, I have found that all opamps I have used do sound better on 2x9V instead of just one 9V. There is a little more headroom and the opamp usually sounds smoother in general... most probably behave better on a higher voltage than their rated minimum that they are sometimes run on.
Since I only build portables, I am stuck with 9V batteries mostly... and 9 times out of 10 I use 2x9V.
Top Mall-Fi poster. The T in META42. Formerly with Tangentsoft Parts Store
Sep 27, 2001
If the op-amp didn't care about voltage, 2x9V would give the same battery life as 1x9V. The reason you get longer battery life with 2x9V in most situations is that the op-amp starts clipping the output signal before 1x9V is fully drained.