Technical question about various amplifiers

C

Champ

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Can someone explain to me how to calculate the maximum current (amperage) that an amplifier can deliver?
We gets specs on total watts, dB gain, etc. but very rarely current delivery.
One thing I've always been told was that if an amplifier can "double down" going into lower impedance loads, that it "can deliver a lot of current". So the best I've been able to find is checking to see how many times the wattage doubles as you approach 1ohm.

Krell is, so far, the only company that I've found that will list this spec specifically.
I've managed to find the number on a few others by exhaustively searching through Stereophile reviews.

I'm just trying to wrap my head around vastly different specs. The Krells state max current in the upper teens to lower twenties depending on model. And they all "double down", or nearly so. The biggest and baddest Boulder is said to deliver 32amps max. And the Music Fidelity Titan is said to be able to deliver something north of 100amps. I think this is fascinating since we are, at best, able to pull 20amps out of a wall. (The Boulder literally has a 30A connector on it's chassis and a 15A connector at the wall. Wut? haha.)

I know that current varies with the complexity of speaker impedance. But shouldn't I be able to come up with some reasonable number for MAX current based on known quantities such as nominal speaker impedance, max watts, dB gain, etc.?

Thanks so much for any help on this. I've been googling till my eyes turned red and still nothing helpful.
 
Um. So now that I've asked the question......
Is it as simple as dividing the peak voltage by the resistance?
:/
 
If you know the power the amp will make into a given load you can calculate the current, which is the square root of power divided by load.
 
You really have to take a manufacturer's specs with a grain of salt as measurements can show an entirely different story. Krell used to really understate their 8 ohm spec to seem like they're doubling down. Here are a couple examples. On their KAV-400xi integrated amp, they showed specs of 200W into 8 ohms and 400W into 4 ohms. Stereophile measurements showed this piece was putting out 290W into 8 and 350W into 4. On their FBI integrated, their specs were 300 into 8 and doubling down to 4 and 2 ohms. Stereophile measurements showed 430W into 8 ohms, 667 into 4 and clipping power with only one channel into 2 ohms was 1020W. While this is all very powerful, the specifications are misleading. Someone thinks that it doubles down based on their specs, but they certainly don't when measured. I'm not just picking on Krell as they certainly aren't the only ones to show a lower 8 ohm spec. I think there are a number of manufacturers that show a realistic 4 ohm spec and then cut that in half for their 8 ohm spec to give the impression of doubling down.
 
There are two current specs! One is the amount of current present when an amplifier is making a certain amount of power into a certain load, as Anatta correctly pointed out.

The other is the one you see in advertising, which is the amount of current present when the power supply is shorted out for 10milliseconds. That's where you see those amazing current specs like 80 amps and whatnot- which for most amplifiers is ridiculous. A lot of people mistake numbers like this as the amp somehow being able to produce that amount of current through the speaker, which in most cases simply won't happen.

Since 80 amps is such a common number, and giving the manufacturer the benefit of the doubt in the math, here's the math:

Power = Resistance x Current squared. So to keep that number down, the resistance (speaker load) will be one ohm for this exercise. That means that the power for 80 amps is 6400 watts! Since there really aren't any amps with that kind of power, we can assume that the 80 amps has nothing to do with the power output.

What it really is, is a statement of how much energy storage is in the output section of the amplifier's power supply. By this measure, one of our larger amps, the MA-2, which is a 220-watt OTL, has a current rating of 50 amps. Pretty impressive for a tube amp, huh?

In short (if you will pardon the expression) the 'current' spec for the most part is advertising and should not be taken very seriously other than the manufacturer has a nice power supply in the amp.
 
Everest Audio said:
You really have to take a manufacturer's specs with a grain of salt as measurements can show an entirely different story. Krell used to really understate their 8 ohm spec to seem like they're doubling down. Here are a couple examples. On their KAV-400xi integrated amp, they showed specs of 200W into 8 ohms and 400W into 4 ohms. Stereophile measurements showed this piece was putting out 290W into 8 and 350W into 4. On their FBI integrated, their specs were 300 into 8 and doubling down to 4 and 2 ohms. Stereophile measurements showed 430W into 8 ohms, 667 into 4 and clipping power with only one channel into 2 ohms was 1020W. While this is all very powerful, the specifications are misleading. Someone thinks that it doubles down based on their specs, but they certainly don't when measured. I'm not just picking on Krell as they certainly aren't the only ones to show a lower 8 ohm spec. I think there are a number of manufacturers that show a realistic 4 ohm spec and then cut that in half for their 8 ohm spec to give the impression of doubling down.
Click to expand...

While some do mis-lead , the main reason for the lower 8ohm number has mostly to do with the THD rating vs power output. If the amp designer wants to have the rated output @.05% thd for eg this power number will be completely different than at 1%thd as used by stereophile.

To the OP ....

To really know look for a 2 ohm bench number, any SS amp delivering RMS numbers into 1&2 ohm will most likely be able to do dynamic power (music) into a loudspeaker load of the same, most likely in your domestic situation you will not be using more than 30-50 watts rms with the rest consumed in peak power ..

Any manufacturer claiming 1&2 ohm stable without an RMS rating Could be an issue at such loads ..


Regards
 
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