[andrzejpw]

Do I have to use a current source to do class A? Or would batterys work as well?

 

[Joe Bloggs]

I have no knowledge about the meta at all but it seems a no brainer to me that the answer should be depends on how many batteries you use...

If the batteries in series can't provide enough current just pair more batteries in parallel until you have enough

 

[tangent]

Quote:

Do I have to use a current source to do class A? Or would batterys work as well?

The only thing class A operation and batteries have to do with each other is that class A operation requires at least ~1.5mA of additional current draw, which may be a problem when running on batteries. Other than that, the two items are completely independent.

 

[andrzejpw]

Hmm. How much mA do batteries give?

 

[andrzejpw]

Ok, a 9V battery may have about 150 maH. So two would be 300, right?

How much does the amp draw, approximataly?

 

[tangent]

An alkaline 9V battery should have around 600 mAh, which means that if you put a constant 1 mA draw on it, it will last 600 hours. If you have a 10 mA load, it will last 60 hours. If you add a 2 mA current source pair, bringing that up to 12 mA, battery life will drop to 50 hours.

The 150 mAh number you saw is undoubtedly for a rechargeable battery.

The milliamp-hour rating of a set of battery goes up by a factor of N (that being the number of batteries) when the batteries are wired in parallel. If you wire them in series, the mAh value is the same as for a single battery, but battery life still goes up: battery voltage ramps down steadily as the battery is drained, and if you put the batteries in series, you start that ramp at a higher voltage, so it takes longer to get down to the "dead battery" voltage. Also, batteries in series can be drawn down farther than a single battery. Let's say you have an op-amp chip that requires 7V to sound good. If you run it with a single 9V battery, it will only be run down to 7V, so it will still have life left in it when the amp starts sounding bad. If you put a second 9V batttery in series, you start at 18V and drop to 7V, where each battery would be 3.5V. Since a 9V battery really won't go down to 3.5V usefully (internal resistance becomes too high) this configuration gets the most life out of both batteries.

 

[andrzejpw]

Yagh, stupid me, yes, they were rechargeable.

I'll be wiring my meta's in series, I think.

How much does a standard meta draw? Is there any way to figure that out?

I'm trying to figure out how much of an impact class A will have on battery life. It looks like not much.

 

[tangent]

Quote:

How much does a standard meta draw?

Would you believe that "it depends"? Here are the major current sinks in the circuit:

1. Buffers. For a simple 3xEL2001 configuration, figure 1-10 mA of draw, depending on load and manufacturing variation.

2. Op-amp. Totally dependent on the chip. See the idle current spec on its datasheet. Add a milliamp or two to give the under-load value, in this amp.

3. Current source? Anywhere from about 1.5mA on up to, oh, 20 mA for the highest reasonable value (10 mA per channel).

4. LED -- a milliamp or two.

You can get this circuit down below 10 mA total. On the other end of the scale, my current records is 40 mA under full load.

 

[andrzejpw]

Ok, so worst case, with 600 ma, It might last about 15 hours.

Good enough for me!

 

[tangent]

That's 15 hours assuming you drain all the batteries fully. If for some reason your configuration doesn't allow the batteries to drain fully, you will hurt battery life.