[gtp]

This might be a silly question, but here goes.

When building an amp, say a Pimeta, what is the purpose of using two 9V batteries? I have been under the impression that more batteries equals longer life, but just thinking about it now, I'm not so sure. In series, you get 18V. Fine. But the life of the amp will be the same whether you use one or two batteries, correct? The current will go up by a factor of two because the voltage is increased, right? Therefore the draw will be the same and the life will be the same for one battery or two. Sound quality will be better for hungrier opamps, but from a lifetime perspective, am I correct?

Please let me know if I am deluding myself (on this topic only, please

).

Thanks,
George

 

[z2trillion]

yeah. you're correct. the battery life will be the same (more or less) for two batteries or one battery. the current won't increase. it just goes through both batteries, and since their mAhr numbers havent changed, both batteries will die after the specified number of coloumbs have passed through them.

 

[trains are bad]

Adding another battery in parallel doubles your battery life. Adding another on series doesn't exactly, but it does typically increas your battery life.

When you bump the voltage up, you raise the rails, which allows you to crank the volume up higher or hit higher instantaneous sounds. If you don't change your volume on the cans, adding another battery in series won't change your current draw significantly. But your battery life will go up because from fresh batteries until the rail voltage drops down to the one-battery level will be longer.

IANAEE, YMMV

(I am not an electrical engineer)

The current draw is what really affects battery life, note battery capacities are in Amps*Hours--Current*Time.

 

[tangent]

Quote:

Originally Posted by z2trillion the battery life will be the same (more or less) for two batteries or one battery.

That's only true if your amp doesn't go into clipping before the one-battery setup runs out of juice. Read this article to get a handle on the working voltage issue. Take care of that first, then start worrying about battery life.

 

[gtp]

Quote:

Originally Posted by tangent That's only true if your amp doesn't go into clipping before the one-battery setup runs out of juice. Read this article to get a handle on the working voltage issue. Take care of that first, then start worrying about battery life.

As usual, good point Tangent. With a 8.4V OPA2107 Cmoy, I knew the battery was dead when I heard crunchy clipping. With the 16.8V OPA2107 Cmoy, I knew the batteries were dead when the volume all of a sudden goes down very low. I can't say that I noticed battery life to be very different between the two (though I never actually measured). Also, I can't say the sound was *dramatically* different, maybe slightly better, but I had no way of doing a blind test so I can't be sure.

[Warning - newbie amp building philosophy to follow] So I guess as with all amp questions there is no clear answer. The answer depends on the opamp, the batteries, the setup, etc. Potentially there could be a gain, or no gain at all. My lesson from this forum in the last couple of months is that designing an amp really is partly an art. Nothing is really black and white - there are always engineering tradeoffs here and there. The key to good design is the *interaction* of the various components, not the individual components themselves. This precludes getting a simple answer to a simple question like, "Are two batteries better than one." The answer is, "It depends." [done]