current versus watts

Seems like all high quality amps clearly describe output in watts , with the best amps doubling output as impedance is is halved. But, I do not see(often) specs on current ? why is this ? Is high current as important to quality dynamic sound as high watts. If so, what are the general ranges of current output that would be acceptable for a high quality amp. For example, if you have a 300 watt/channel amp that doubles from 8 to 4 ohm, what would be strong current output ?

Apologize for the simple question and feel free to direct me to earlier post that might deal with this issue
Is high current as important to quality dynamic sound as high watts.

You can't separate the two as current and power are proportional.

current = square root of (power divided by ohms)

300 watts into 8 ohms takes about 6.12 amps of current

600 watts into 4 ohms takes about 12.24 amps of current

Some amps can handle delivering the current needed for 8 ohms at full power but run out before they can deliver the current needed for full power into 4 ohms.

The better way to say it is that the amp has to be able to deliver enough current to develop the requested power, not which one is more important.

Herman: thanks for the response. then, is it fair to ask when looking at an amp what the max current is and view it as a minimum threshold. for instance, in the example above, if the amp can produce 12.24 amps at 600 watts (and also assume a really high quality amp that doubled again to 2 ohms)and 24.48 amps at 2 ohms that is fine. Is there value to "headroom" on the amount of current needed?


>>“Seems like all high quality amps clearly describe output in watts , with the best amps doubling output as impedance is is halved.”<<

You don’t actually think that do you?

Nearly every body is aware of the term ‘watts’ as it applies to an amps output…. Even novices & beginners, to one extent or another. Some will even say an amp is better than another due to the watts it puts out…. But such statements are quite shortsighted and very inexperienced.

“Watt” is the representation of the relationships between curren, voltage, and resistance or load.

Watts = an easier way to describe one facet of amplification usually…. It’s not the end all be all of amps however. I wish it were that simple!

From a somewhat less naive perspective, it could be said one amp is subjectively ‘better’ than another, without respect to the power output characteristics, judging by the sound of it instead…. Or by how much it sells for… Or by it’s design topology… Or merely by it’s classification, A; A/B; D; Tube; SS; Transformer coupled, truly balanced, or even it’s output devices.

However, there are other deliberations which will conclude if one amp is bested by some other… not purely by it’s numbers.

Whether or not an amplifier doubles up it’s power output as impedance is halved, is one thing…. Maybe a mechanical need or maybe not, for some, but as the sound being produced is of paramount import, how it produces power should not be the singular consideration or even a thoughtful way to categorize which amp is better than another at all.

When the specs of an amplifier gains more respect than does it’s voice… within reasonable thought to the application, inordinate frustration and suffering may ensue due to the lack of synergy any old amp will yield once set into a finely tuned existing setup, just because it’s power doubles down!

Still common ground needs be in place so all can speak ‘audio-ese’, at least a little. Amp makers start saying this one puts out 5.5 A or 85 V, and darn few will be able to apply such info as they seek the right sound/amp for their intended purposes. So they use a commonly known term more can relate to with which to somewhat better position their power products into.

It is indeed about far more than the amount of watts on tap very often. Usually it is about what kind of watts, instead.
Amps aren't rated for "max current" since that depends on the load. Most amps are voltage amplifiers; they try to hold the output voltage at a certain level for a given input and the amount of current they produce depends on the load. The 300W/8ohm amp above produces a maximum of 49V. This 49V divided by 8 ohms is 6.12 amps (Ohms law.) If the load drops to 4 ohms then it will still try to maintain the 49V so it needs to deliver 12.24A. If loaded with 2 ohms it will try to deliver 24.48A, try to deliver 49 amps into 1 ohm, and so forth. At some point any amp will be unable to deliver the required current.

All else being equal an amp that can deliver more current is preferable over one that can't, but things are never equal. Some speakers have big dips in their impedance at certain frequencies and theoretically benefit from a high current amp, or better stated benefit from an amp that can deliver high amounts of current when required to do so. So yes, this headroom is a desirable characteristic if the speakers you are using call for it but is not the sole criteria for picking an amplifier.

If you google Ohms law and speaker impedance and you can find a wealth of material about these fundamental concepts.

Sound quality has little to do with current (otherwise the tube industry would have died decades ago) and has everything to do with distortion. That is a topic for a different thread.

'Current' is an issue about which there is a lot of mythology. see:
"Sound quality has little to do with current"
is a half truth. It depends on the speakers impedance curve.
Chrisr-your aware of who Atmasphere is right?
" The amount of current that flows through the POWER SUPPLY when it is shorted out for 10 milliseconds. That's the official spec. There are a number of tube amps with ratings that high. So when you see the idea of 'current reserve' being bandied about, keep this in mind. "

Thank you Athmospere, you are absolutely right. Spectron also makes the same point (well, their reserve of 65A lasts 500 msec with peak power of 3500 watts per channel)

I would add to your comments that luck of needed power (voltage or current) leads to distortions and you and Spectron wrote that this type of distortions (particularly in ss amps) is odd order harmonics producing ear piercing sound.

Thank you again!

My panels have a 4 amp fuse on the mid/tweet. I simply can't see them making use of much more than about 7 or 8 amps continuous...though i may be wrong.

As for my ICE amps 45amp rating?


Can anyone point me at a fuse time/current chart which will show HOW MUCH overcurrent a fuse can take and for HOW LONG?
I know fuses are NOT a 'brick wall' already.
I would think it would be on a spec sheet for that particular fuse; I would start with the manufacturers website and look at a spec sheet if there is one.
Magfan -- I second Rleff's suggestion. For instance, the site provides datasheets indicating opening time vs. current overload percentage, and also a nominal melting figure in units of ((amps squared) x (time)). I assume other manufacturers have similar information as well.

Best regards,
-- Al
with the best amps doubling output as impedance is is halved.
you're talking audio, man! what's 'best' for you could be 'trash' for another listener! There's no objective definition of 'best amp' in this hobby - it's all VERY subjective.
So, I'd say that many of the large chassis (think Rowland Model 8, 9, the MBL 1200W/ch used to drive their radial speaker, Gryphon & others in that chassis size) & expensive amps (think top-of-the-line Krells from the late 1980s, present MBLs, Boulder, Rowland Model 8, 9, Gryphon) show this tendency. Most amps in the market do not have this proprty - it's very expensive to make them have this property!!

Seems like all high quality amps clearly describe output in watts........
But, I do not see(often) specs on current ?
That's because Power = Volts * Current = Current squared * Impedance (or Resistance). So, if you know Watts & Resistance you can calcuate the output current. Herman has already done those calculations for you in an earlier post. Those calculations pertain to maximum output DC current of your hypothetical 300W/ch into 8 Ohms i.e. output current when the amp is outputting 300W. You should realize that such an event is unlikely to occur frequently unless you are listening to music at paint peeling high levels (& ruining your ears!).

Is high current as important to quality dynamic sound as high watts.....
If so, what are the general ranges of current output that would be acceptable for a high quality amp.
yes & no - depends on the speaker you are using. Some speakers are notorious for needing a large reserve of current to drive them to their best performance & other speakers are an easier load on the amp. Hence, there is no clear definition on what is considered a general range of output current. As another member pointed out - depends on the speaker impedance-phase curve.
But, as Atmasphere wrote before, whether you output small amounts of current or large, you need to do so with minimal distortion otherwise the sonics are strident. At high distortion levels it won't matter whether you have the "best" amp or not, the music experience will come up way short.

The conclusion is that the amplifier-speaker interface is a complex one because the speaker load affects the amplifier output impedance & vice-versa. Plus, the speaker impedance & phase varies over frequency. So, as you run up/down the audio spectrum, nothing remains constant! So, you will not be able to take a fixed number (amplifier output current as you are asking) & apply it to an interface that has variable performance....
When we are talking 'best', IMO power doubling has nothing to do with it; none of the 'best' amps I have heard have that capability.

I feel that the specs have no meaning if the resulting amp is unlistenable. IOW our ears are more important than the amp is- our ears are the most important aspect of audio. Its important to drop all the preconceived notions about specs, including the ability to double power, if you your goal is for the system to sound like real music. see

for more information
".... output current when the amp is outputting 300W. You should realize that such an event is unlikely to occur frequently..."

Well, measured (MEASURED!!!!) peak power needed to drive B&W 805 bookshelf speakers at musical peaks waw 3500 watts i.e. not three hundred but more then three thousand watts and for 87.5 dB sensitivity bookshelf speakers.

Only Simon Thacher from Spectron (to the best of my knowledge) is trying to "connect" specs of their amp with its musicality and many, me including, compare their amps to the best tube amplifiers.

The problem is not in specs. The problem to read them and understand them. The problem that many of not most amp producers show misleading specs like we discussed above peak current for 20 msec or displaying distrotions at low (typical number is 10 watts) output and not full output and at 1kHz only etc etc.

So, yes - you are better off listening to the component but it does not hurt to understand too...

John and Simon's philosophy is iltra low distortions and then you hear real (well recorded...) music without ear piercing or euphinic colorations.

Hi Dob, I agree keeping distortion down is important. Distortion can hide detail. A lot of designers use global negative feedback to reduce distortion though, and this technique often results in subtle enhancement of odd ordered harmonics, specifically the 5th, 7th and 9th, that are used by the human ear to perceive the volume of a sound.

So the resultant sound will sound louder than it really is, in addition it will have brightness. Our ears are so attuned to these harmonics that even 100ths of a percent of distortion of them is audible: harsh, hard, brittle, clinical, bright, chalky, etc are all terms audiophiles use to describe this enhancement.

Thus it is often the case that the use of negative feedback is violating one of the fundamental rules of human hearing perception. So generally an ultra-low distortion figure is often a sign that global negative feedback is being used, and also that the amp may sound like a nice hifi, but will never sound like real music. IOW I am always suspicious when I see super low distortion figures.
"use of negative feedback is violating one of the fundamental rules of human hearing perception. "

Hello Ralph,

I spoke with Simon Thacher from Spectron and he is in full agreement with you as it relates to negative feedback in conventional amplifier.

He said that you are absolutely right and poor neagtive feedback, ripples from the power supplies and few other sources of odd harmonic distortions are "music soul killers" i.e. its not so much obsuring detail by even order harmonics as ear-piercing odd order harmonics.

Yet, Spectron rely heavily on global feedback. He explaiend that the crucial factor in negative feedback is transit time, the amount of time it takes from when an error is detected at the input until it is corrected at the output.

Thacher claims that Spectron use much faster digital logic circuits then anybody in the world. Their amp's transit time is less then 200 nanoseconds. Such an ultra-short transit time allows the amplifier to correct for many small errors; and the control loop can follow the input much more accurately WITHOUT generation of many odd (and even) order harmonic distortions and this is the main reason for positive "musical" reviews their amp receive.

All The Best
Dob, yes, the transient time, propagation delay, plays a huge role in the effectiveness of global loop feedback. I am not sure exactly how fast an amp has to be though; even the fastest amps I have seen seem to have problems when feedback is applied. IMO the amp should be functional with or without it feedback.