When does high current capacity capacity matter?

[davmol]

I'm noticing a trend in amplifier listings, particularly on more expensive lines / old school brands, that their marketing schpiel includes "high current capacity". I'm assuming this is a way to try and separate their offerings from the cheaper high power / low SINAD amps.

So I know nothing about this subject and am interesting in what scenarios the amplifier current capacity matters, and when or if the issues that it solves are ever audible?

 

[Roland68]

I'm noticing a trend in amplifier listings, particularly on more expensive lines / old school brands, that their marketing schpiel includes "high current capacity". I'm assuming this is a way to try and separate their offerings from the cheaper high power / low SINAD amps.

So I know nothing about this subject and am interesting in what scenarios the amplifier current capacity matters, and when or if the issues that it solves are ever audible?

As you've already noticed, "high current capacity" is used as a marketing term, and without any real power specifications or measurements, it's worth about as much as a piece of toilet paper.
Power consumption/performance depends on the frequency range (the lower the higher) and the impedance (the lower the higher).
For example, it's no use if you have impedance-critical 4-ohm speakers with a minimum impedance of 2 ohms, and the amplifier has a "high current capacity" at 4 ohms, but not at 2 ohms.

 

[MaxwellsEq]

I'm noticing a trend in amplifier listings, particularly on more expensive lines / old school brands, that their marketing schpiel includes "high current capacity". I'm assuming this is a way to try and separate their offerings from the cheaper high power / low SINAD amps.

So I know nothing about this subject and am interesting in what scenarios the amplifier current capacity matters, and when or if the issues that it solves are ever audible?

If you search ASR, you will find many threads about how much power is needed to drive certain speakers.

But power is not necessarily the best metric. Any electrical load requires both current and voltage. Pure resistance loads are very rare in loudspeakers, reactance is more the norm. So at some frequencies the speaker has a more capacitative load and for other frequencies a more inductive load.

In a pure resistance, as the voltage applied is increased, the load "demands" more current for the voltage to be achieved (a bit of a simplification). We can use the standard formulae to work this out: v^2/R and I^2xR. Give it a try. We can frequently show that many amplifiers are quite able to supply enough current. But for highly reactive loads, the voltage and the current can be significantly out of phase, which will demand potentially more current on average than the pure resistive load.

Higher current leads to more heating. So amplifiers need more robust output devices, thicker tracks, more PSU capacity, greater cooling etc. than they appear to need if you look at burst sound peaks or pure resistive loads.

 

[Pareto Pragmatic]

So I know nothing about this subject and am interesting in what scenarios the amplifier current capacity matters, and when or if the issues that it solves are ever audible?

I know just enough to have bought an amp where I will never have to think about this again. Purifi ET400A based.

As a practical matter, you can just look at your speakers (8 or 6 or 4 ohm) and make sure the amp is rated for that resistance. The typical amp ratings are for 8ohm, and if they don't list 4 ohm watts, I would avoid that amp for a 4 ohm speaker. Amp specs are usually given for 8 ohm loads up front, but looking for what they do for 4ohm might take more looking. As a rule of thumb, using the marketing speak, I would say that a 100w/8ohm amp that goes to 200w/4ohm is "high current". If it only goes up to 150w at 4ohms, I would not call that high current. Definitely not as high, that's for sure.

The lower the resistance, the more important current becomes.

What it sounds like is distortion, particularly in the bass. Things might sound flat, dynamic passages might not be dynamic enough. So those are the main issues more current can solve, if that's the cause and not something else.

If I wanted to demonstrate how this sounds to someone in the room, I would use my headphones, which are Hifiman XS (one of the best deals in audio I would say). Not terribly hard to drive for planar magnetic drivers, but they do benefit from some oomph.

Play on my phone with a $20 dongle, flat, play with my $300 AVR headphone jack, flat. Dull, sounded no better than my $20 IEMs either way. And I never listen to headphones loud, but I was still cranking the volume pretty high for those two amps.

With a Topping Dx3 pro? WAY better! More current, more oomph, much clearer sound. At the same volume (close to it, by ear not by dB).

That's my practical, not very technical take on the issue, fwiw.

 

[LTig]

High current capability is a marketing buzzword. If it is not backed by a high power specified for loads at 2 Ohm or better 1 Ohm, it's a lie.

It just means that the amp can deliver lots of current for loads with very low impedance. If you buy such an amplifier to feed 8 Ohm loads it's a waste of money.

 

[davmol]

Thanks for the responses. For example, I run Fosi V3 monos for Wharfedale Linton 85th speakers (6 ohm rated, but dipping as low as 3ohm according to Erin). They are running on a 48v 10amp supply, so 5amp each. I see the main challenge to something like this amp, given it can't really be on power output or SINAD or response, is that it is "current limited" / needs more amps (but not wattage apparently...). I don't want for anything more, I'm just interested to know if it's largely nonsense.

 

[Roland68]

Thanks for the responses. For example, I run Fosi V3 monos for Wharfedale Linton 85th speakers (6 ohm rated, but dipping as low as 3ohm according to Erin). They are running on a 48v 10amp supply, so 5amp each. I see the main challenge to something like this amp, given it can't really be on power output or SINAD or response, is that it is "current limited" / needs more amps (but not wattage apparently...). I don't want for anything more, I'm just interested to know if it's largely nonsense.

Amir measured the short-term performance with the 48V/5A power supply and that should be more than enough even at 2 ohms.
If you think the power supply is limiting you, just get a second one.

 

[davmol]

Thanks for all the answers. I'm inevitably going to sound like my wife now, but I'm not looking for a solution to a problem, I'm just interested

 

[Roland68]

Thanks for all the answers. I'm inevitably going to sound like my wife now, but I'm not looking for a solution to a problem, I'm just interested

Come on, admit it.
You're looking for a problem to justify to your wife the next additional expenditure on your hi-fi hobby...