Originally Posted by headfone
In case MisterX's hint is too subtle, what you have there is a battery, not a cell. A battery contains two or more cells. Chemistry dictates cell voltage. NiMHs are 1.2 V per cell, alkalines are 1.5 V per cell, lead/acid cells are 2 V, and lithium cells vary between 3.0 and 3.6 V depending on flavor. All of these are nominal voltages; do some Googling if you want all the hairy details.
A 9 V battery is composed of 3 to 8 of these cells, in series, depending on chemistry and the exact terminal voltage and capacity they're shooting for.
|What's your experience with running Pimeta (v.1 and/or 2) on a single 9V cell?
It's doable, with that chip. My tests
found that it doesn't start clipping until about 6-7 V under headphone load. It's probably closer to 5 V with no load, as in a PIMETA v2, where the headphone load is handled by the buffers. You almost certainly lose out on some usable capacity, and the op-amp may not sound its very best, but I've done it successfully.
Try 2x9V in series, if you have an extra battery one hand. Realize, however, that having many cells in series brings its own problems. TANSTAAFL.
Also consider trying a rail-to-rail op-amp. The AD823 or AD8066, for instance.
|But given the Pimeta's current draw (esp. WRT its buffers), I'm not sure a single 9V cell is a wise choice.
Actually, the high current draw is one of the reasons not
to string too many cells in series. There's a constant (small) amount of resistance per cell, so adding more is a tradeoff, not a clear win. Another problem with too many cells in series is an increased danger of cell reversal. There's a reason you don't find 18 V batteries on the commercial market.
(Before anyone goes Googling to find such a thing, I have no doubt one could be found. Before you post, please consider how many sigmas they are out from the peak of the sales volume curve.
Originally Posted by amb
The recommended minimum supply voltage is +/-5V, and add the fact it is not a rail-to-rail opamp (it clips at 1V below each rail), results in a rather sub-optimal combination.
All true. The datasheet does say that, and the op-amp does clip as you describe.
The thing is, a 5 V rail-to-rail supply less a volt per rail leaves room for about 1 Vrms, enough for many headphones. The terminal voltage for a 9.6 V NiMH "9V" battery starts dropping fast below about 8 V, where we have room for nearly 2 Vrms to the headphones, which covers just about all dynamic headphones on the market.
1x9V may not be ideal, but it may be practical.