[till]

I would like to increase my CMoy's battery life while I'm waiting for parts for my next amp. Currently, it is set up like this:

1. Levallois design with Meier crossfeed, see http://headwize2.powerpill.org/proje...2a_add_prj.htm (near the bottom of the page)
2. 2 x OPA2132, gain of 4, dual 20k linear pot with 10k shunt resistors (I might change that, it was just a quick fix because I didn't have any other resistors)
3. Tangent's BUF634-based virtual ground, see http://www.tangentsoft.net/audio/cmo.../buf634-ps.png , with 470 µF power caps
4. red power LED (generic) with 10k resistor, 3 mm
5. 2 x 9V battery

It drains two cheap 9V alkalines in about 10-20 h of usage. What could be the biggest culprit? I know that a low current LED would be better (could be a huge saving, i. e. 10 mA vs. 2 mA or something like that?). A TLE2426 instead of a BUF634 would reduce current draw by another 1.4 mA. I wouldn't want to do a complete redesign, i.e. rip out one of the op-amps and make it a standard CMoy. Any other thoughts?
Can battery life be significantly improved with these or other means? Otherwise I'd have to build a NiMh charging circuit because at this rate, I'm too cheap even for cheap alkalines

 

[guzzler]

the LEDs current draw is determined by the resistor, so assuming it's a 2.5V LED, the current drawn is 1.55mA. The low current LEDs just maintain a set level of brightness to a lower current.

You'd actually save quite a bit more by switching to a TLE, as 1.6mA is dissipated in each of the splitting resistors, so figure about 4.6mA for that change.

There aren't any major things you can do with that setup. You could change to AD823s, but they really need to be buffered. On the whole, Analog Devices chips have a lower current drain than Burr Brown, but tend to have a weaker output.

NiMH batteries are a very good investment anyway, they'll pay for themselves in no time, and they have a lower internal resistance. And they're good for the environment

g

 

[till]

Thanks, guzzler

So I'll get a TLE. And for starters, I'll switch the op-amps with OPA2604s that I ordered -- they seem to have a lower current draw than OPA2132s, if I interpreted the datasheets correctly. And then maybe some ADs (hard to get here, just like the TLE).
Regarding NiMh batteries and charging circuits, do you have a recommendation for a specific IC? I'm one of those persons who frequently wouldn't remember to turn off the charger in time...

 

[guzzler]

check out the battery charger on tangents page in the PPA section, that should get you started

g

 

[PinkFloyd]

Try some Iron Pyrite energised play dough with krypton energised silk fibre power rods......... £9.99 from Maplins.

hehe

Drunk Birthday Pinkie

 

[till]

Happy birthday, PinkFloyd

Have a good time!

guzzler, I did a quick search -- Tangent uses the MC33340, which unfortunately is unavailable to me (I could get the SOIC version, but somehow I don't want to

). Alternatives seem to be the MAX712 and the BQ2004, according to this site:
http://pc1-archbo.bot.unibas.ch/~pas...tml#controller
Both are available, I'll try one of those. Thank you for the advice!

 

[tangent]

Quote:

2 x OPA2132

That's part of the problem. A straight CMoy amp with Chu Moy's modified Linkwitz crossfeed would save you one chip's quiescent current.

The OPA132 runs about 4mA per amplifier, so this would save you 8mA. Further down that path, you could change to a more efficient chip, like the OPA227 or the AD8610. These have high enough output currents for use in a CMoy, unlike the AD823.

Another thing about op-amps is that some run to lower supply voltages than others. Since the batteries drop in voltage over time, this can give big improvements in run time. The two chips I've recommended should be more efficient in that way than the OPA132 as well.

Quote:

Tangent's BUF634-based virtual ground

That isn't the most efficient circuit in the collection. The divider draws about 0.4mA at 18V, and the buffer another 1.5mA.

You could increase the divider resistors to 100K or so. That drops its draw to less than 0.1mA at 18V, and lower as the batteries drop in voltage.

Going to a bare TLE2426 is a good idea, too. This isn't universally evil like some people will tell you. Witness the number of happy MINT users. A TLE only draws about 0.3mA, and its output impedance is lower than for a BUF634 so it might even sound better to you.

Quote:

Alternatives seem to be the MAX712

The PPA battery board circuit is way more heroic than you need to be for this project. A simple MAX712 charger will work just fine for your purposes. You only have to get heroic when your battery pack runs 20V+ or more.