[ciphercomplete]

Quote:

Originally Posted by Gradofan2 /img/forum/go_quote.gif But... in general... I think you'll find... amps with very low output impedance have more output current than amps with moderate to high output impedance - so you might use output impedance as a "proxy."

Sounds like a plan.

 

[nikongod]

Quote:

Originally Posted by PhaedrusX /img/forum/go_quote.gif i'm curious about this, as well. output current specs for amps are helpful, but i wonder about the needs of the headphones themselves.

very low. headphones dont need much current, even low impedance types RARELY take more than a few ma unless you listen LOUD.

The key to all of the "big power" headphone amps is how cleanly they drive the low impedance headphones.
Quote:

Originally Posted by Gradofan2 /img/forum/go_quote.gif I'd email Grado labs... and... ask them what the output current is for their RA-1 AC amp, as well as their recommended range of output current.

The chip used in the RA-1 is able to output LOTS of current for an opamp. About 70mA per channel, per the datasheet.
The opamp does not run fully class-a though, so an amp with less output current, but full class-a could (and often will) sound better. The RA-1 does have great synergy with grados though.
Quote:

Then... I'd email the vendors, or mfrs, of the amps you're considering and find out what the output current is.

very little in tubevile is this high, but it is all class-A (for headphones anyways), where the ra-1 is class-ab. BIG difference. I think both the extreme and zanadeux come CLOSE, but even a morgan jones with VERY little output current can get a grado going LOUD before it clips.
Quote:

But... in general... I think you'll find... amps with very low output impedance have more output current than amps with moderate to high output imedance - so you might use output impedance as a "proxy."

eeeh, this is a decent rule of thumb, but there are stumbling blocks.

It is totally possible to make an amp with a 1 ohm output impedance that cant supply more than 2ma. The output stages of many preamps are constructed this way. My EQ is fully class-A and has a 10 ohm output impedance, but the output stage falls to class AB when driving anything less than about 10K ohms.

 

[paul_lindemann]

Watts mean very little, comparatively speaking. Current (usually measured in Ampres) and peak current tell you alot about an amps ability to respond to the dynamics of a musical passage. Also tells you alot about the manufacturer.

Of course, the amp has to sound natural and musical as well...which has nothing to do with the current and power supply.

The Belles Hot Rod, The Edge NL series, and the Stratos all have nice current...also plinius!

 

[majkel]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Uhm... look at specs for output current. Don't worry about the whole WATT thing, with headphone amps, it'll be small and greatly dependent on power supply voltage since a Watt is Volt*Amp. In headphone audio, it's pretty meaningless. Consider this case: Mini3 has OPA690 on ground which can sink about 90mA per channel and swing 1V away from rails. 90mA * 3.2V = 0.36Watts (8.4V battery) and this amp will drive most headphones nicely. CMOY with OPA2132 running off 24V PSU would be 40mA * 24V = 0.96Watts. It has 3x higher Watts and it won't drive current hungry headphones that well.

OPA690 won't feed more, either because it provides 90mA for both channels which means 45mA per channel. Not impressive.

To the OP - stupid but working method is to use big, low impedance headphones. Play some bass-thumping music and see how loud it can go without clipping. If it happens at moderately low volume, then the amp is not intended for low impedance headphones.

 

[amb]

Quote:

Originally Posted by PhaedrusX /img/forum/go_quote.gif if a typical PPAv2 outputs 25-30mA, a Millet Max ~50mA, and an M^3 80-100mA

Those are the amps' recommended default idle currents, not their output current rating. The latter is much, much higher, limited only by the power supply and the capability of the output transistors.

Quote:

Originally Posted by majkel OPA690 won't feed more, either because it provides 90mA for both channels which means 45mA per channel. Not impressive.

FallenAngel already did the divide by 2 (and then some) in his post, the OPA690's output current capability is 190mA. Also, a straight divide by 2 is not a good way to determine the actual performance unless you listen in mono. Real life (stereo) music means that the chip can deliver more than half of its output current capability at most given instances of time.

 

[PhaedrusX]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Those are the amps' recommended default idle currents, not their output current rating. The latter is much, much higher, limited only by the power supply and the capability of the output transistors...

oops...thanks for clarifying, amb.