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tant caps? newby build question

post #1 of 2
12/19/09 at 7:18pm
Thread Starter 
I am looking at building a verry small op-amp based amp to compliment my clip.
It will be powered by a 7.2v (possibly a 10.8v) Li-Po battery.
To save space I was thinking of using SMD Tantillium caps on the power rails, as well as the V+/V- (using a TLE2426CLP rail splitter).

I was wondering if this is a good idea?

I know the P-51, very similar to what I'm thinking of building, is basically a rail splitter, op-amp circuit. It's also powered by a Lithium ion battery, but it has no power rail caps at all.

so a second question i have is due to the high discharge rates of Lithium-ion/lithium-pol. batteries, are power caps even needed?

Thanks, Joe
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post #2 of 2
12/19/09 at 11:18pm
Tantalum capacitors look great on paper, even if they're a little pricey. They have one unfortunate property that makes them impractical for a lot of things. When they go bad, and they go bad easier than any other type, they tend to short. If you can find the space, use an electrolytic. If you can't, keep trying.

I'm sure a lot of people can answer the second question based on a lot more practical experience than I can, but... Discharge rate isn't really the relevant point. What matters is the ability to deliver a short burst of current. Batteries really don't handle that well. I can't give a definitive answer because I'm aware of some very practical situations where a battery is quite sufficient, and the capacitor redundant, but I have no idea if that applies in general with audio op amps. I think it depends on how much dynamic current you're supporting, and whether the peak burst current is within spec for the battery. I'm also concerned about nonlinearities relying directly on a battery: I think the internal resistance depends on the current. Personally, I'd always use a capacitor. If nothing else, it reduces the transient stress on the battery which can shorten its life, both short term and long term.
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