High Current vs high power


Hi!

Often you hear/read comments that the current matter more than the power (example Nait) and one should look for high current more than high power etc.?

Can anyone explain that or debunk the myth (my limited physics knowledge tells me that power and current are interrelated for the same voltage and impedance)?

Also, which amplifiers (pre power or Integrated) have 'higher current' than their peers at same power ratings? Is there any specification that shows the current capability of the amp which one can read and compare? like power, THD etc.?

Thanks
K
kelpie
Most speakers like high current. The signal going into a power amp is usually high voltage and low current. The amp reverses this to low voltage and high current. In solid state amps if the power doubles from 8 ohms to 4 ohms it probably is high current. In tube amps it is usually a function of how big the power supply is.
Alan
I have generally found that hi-current designs exhibit better control over the woofers and tend to sound more "ballsy". Given a choice between 2 amplifiers, I will almost always opt for the high-current design...

-RW-
This is a commonly misunderstood concept in amplifiers. What is meant by 'high current'?

Does it mean that the amplifier behaves as a voltage source, and so can double power as the speaker load is cut in half or does it mean something else?

It means both but often not at the same time.

However it might be helpful to run some math once you see the advertised 'current' figures for a particular amplifier. I remember one amplifier advertised 80 amps. That seemed a bit crazy to me, so I ran the math, and gave the amp the benefit of the doubt. Here is what I came up with:

The Power formula is Power=Current squared times Resistance.

So if we have 80 amps and a one ohm load, the resulting power is 6400 watts (the 'benefit of the doubt was that I allowed it to drive one ohm- do the math for four ohms and you see what I mean). The amp in question did not claim to make any such power, so its obvious that the current rating meant something else.

What it means is the amount of current that is seen when the power supply is shorted out for 10 milliseconds. It is a measure of power supply capacity and nothing more. Can this affect authority in the amp? Sure- as the additional capacity can reduce intermodulation distortion at higher power levels. That has a direct effect on impact.

Just to give an additional bit of information- to make 1000 watts into 4 ohms the amplifier will need to make 15.81 amps. That's all!

IOW, most of the time when you see that expression- 'high current' it has nothing to do with the amp's ability to deliver power. And ultimately it is power that drives the speaker, and power is the combination of current *and* voltage.

You also have to be careful of the speaker. Not all speakers like an amplifier with a super low output impedance- some will play bass with more extension and impact if the amp has a higher output impedance (and such an amplifier might not be described as 'high current'). This is because there is more to it that just simple low output impedance in the amp; there is some physics involved.

For more about this see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
I, of course, agree with all of Ralph's (Atmasphere's) well stated points. I would just add that the miniscule amount of time for which a "high current" amp can provide large amounts of current into a dead short (10 milliseconds, or 1/100th of a second in his example), is generally not stated when maximum current specifications are presented. Which makes the 50 ampere or 80 ampere or 100 ampere kinds of numbers that may be presented for some amplifiers even more meaningless, because chances are those numbers for different amplifiers are based on different amounts of time.
08-25-13: Arh
The signal going into a power amp is usually high voltage and low current. The amp reverses this to low voltage and high current.
Alan, based on your posts I've seen in the past I suspect that you are sufficiently knowledgeable that you must have composed this statement before having your morning coffee. The voltage-related parts of it, that is. :-)

Regards,
-- Al
Al and Ralph, it amazes me how this technical issue just keeps on giving.

I think the whole subject could be mooted if every speaker on the market was required to have an 8 ohm ruler flat impedance curve and zero phase angle curve as a function of frequency response. That way all speakers would be tube and SS friendly.

Well, I also believe in the Tooth Fairy and Ariel the Little Mermaid so anything is possible.

To the other guys -- please don't take this post as a put-down. This issue has had me bogged down for over a year now. So count me in as a card carrying member of the confused society, but just a little bit less so today thanks to Al and Ralph. Just check my other posts.

Regards,

Bruce
"To the other guys -- please don't take this post as a put-down. This issue has had me bogged down for over a year now. So count me in as a card carrying member of the confused society, but just a little bit less so today thanks to Al and Ralph. Just check my other posts."

I don't see why any of this can be so confusing. If you take the technical info, such as Al and Atmasphere have provided, and suppliment it by listening to different combinations of amps and speakers, it should all fall into place. Picking audio components is mostly subjective. You can't bypass listening and hope to be successful. You can get sound to come out of just about anyting, but for good sound, only you can decide.
^^ Yes, audiophiles have seen those pesky spec sheets for amplifiers for decades, but so little on them tells us what is going to sound right that you still have to do the audition. More fodder for the objectivist/subjectivist debate...
Have a Rowland 8T has both over 250 CH plus High Currant i have both.
Zd ... more than you know, I agree with what you said about live auditions. A while back, I posted a comment about road testing two sets of speakers at a dealer friend's shop. Coincidentally, he had just taken in trade an ARC VS-115 tube amp, which until a week ago was the amp I used. That's about as good as it gets for "A/B'ing" speakers. I was quite surprised that a speaker similar to my current fronts ("Brand P") cleaned the floor up with Brand X. Was it the gear, the room, the cables, the amp??? Dunno. But in "theory" Brand X should have cleaned up the floor with Brand P. Go figure.

But here's the dilemma. How often can one fairly audition speakers, amps and other gear given the paucity of high end B&M stores? Forget being able to control all the variables, like using the same model amp when comparing speakers. At least in my neck of the woods, forget taking gear home. Doesn't happen.

OTOH, I find the subject of speaker/amp electrical compatibility interesting. Grasping the variables, many of which are EE design trade-offs, is challenging. But that's me.

Cheers

Bruce
EMB you are a lucky man !!!!
The Rowland 8Ti is a good example of what I was talking about.

Into 4 ohms it is rated 400 watts, but the current figure states(from the website):
50 amps continuous, 100 amps peak

Its pretty obvious this has nothing to do with power! 50 amps continuous into a 1 ohm load would be 2500 watts, yet we can see from the specs that the amp is unable to double power between 8 down to 4 ohms. Even it if could continue to double power to 1 ohm, the output power would "only" be 1600 watts.

What is being stated here would seems to be that the power transformer can provide 50 amps on a continuous basis. I suspect though that if that were to actually happen it would blow its mains fuse in less than a second.

So what we can conclude without speculation or debate is that this 'current' figure is not a real-world spec so much as it is a measure of the capacity of the power supply. I have seen, FWIW, tube amps with this much and more 'current'.
"But here's the dilemma. How often can one fairly audition speakers, amps and other gear given the paucity of high end B&M stores? Forget being able to control all the variables, like using the same model amp when comparing speakers. At least in my neck of the woods, forget taking gear home. Doesn't happen."

I agree that you can't control all of the variables. The good news is you don't always have to. I'll use myself as an example. I'm very picky when it comes to high frequencies. If a system can't get hf's right, I can't listen to it. I don't find it too difficult to judge components in this area under less than ideal circumstances, like a dealer. Given the fact that hf's are very directional, room acoustics don't factor too much into the equation, at least for me. As long as there's nothing in the way between myself and the tweeter, I can usually pick out what I need to.

Now look at another area; Bass. That's much more difficult because the room is so important. That doesn't mean a demo is worthless. Trying a certain amp with a certain pair of speakers can, at least, give you some info, but you are still taking a chance without listening to the system in your room.

So, where I'm going with all this is to say that you shouldn't give up on demoing equipment just because you don't have ideal conditions. Pick the areas of sound quality that are most important to you, and focus on those. Sometimes you have to get creative. Sometimes you have to have to take a road trip. That's just the way it goes. I learned from some very costly experiences, myself. I have no problem at all driving several hundred miles to get to the 1 dealer that will lend me the CD player. And then drive 2 states over because that's where the speakers are. (With the rest of my system in the car, of course). Why? Because its so much easier to spend it, than earn it!
08-26-13: Bifwynne
Al and Ralph, it amazes me how this technical issue just keeps on giving.
LOL! & so true...
but it's good to see that more & more people are beginning to ask this question & are desirous of understanding this electrical interface. This is good! I'm reminded of a clothing company that I * think* is no longer in business - Syms - their slogan was "an educated customer is the best customer". I feel the same for this hobby (obsession?) of audio. The more the users understand, the more the manuf will be vary of try to pull wool over the users' eyes & the more truthful the specs will be.
On the flip side - Look across the pond in the EC countries - hardly anyone over there buys audio equipment based on specs. And, they manuf some really nice sounding gear!
In the USA (& maybe Canada too?) we are obsessed with specs & make that our guiding light in our decisions....

Kelpie, i 2nd Bifynne - read his other threads where several of us have contributed to clearing up the air. It's extensive reading but it will help a lot.

Bombaywalla +1 a thousand times. Over many years I have discovered specs are really useless. Not even a guideline (like I used to think). It's all about total system synergy. Certain components work better with others and will be horrible with others. Best to take advantage of in home demos. Second would to audition at a friends or dealers with as much of what you own and want to keep (evens if it means bringing some of your own equipment - I've done it). I understand that isn't always possible so if you post a thread best to include Equipment - Room Size - type of music and what sound you look to change. Very important also what you like and don't like.

Ok that being said I didn't answer you question but here is an experience I had. Had a Bryston B100sst driving Dynaudio C1's which is rated at 85db The Bryston B100 was rated @ 180W at 4ohms. I thought more power would make the Dyn C1's sound better. I found 2 integrateds that sounded much more powerful especially in controlling the sound. Naim Supernait and Octave V70se (both rated at 70W). I bought the Octave and have since upgraded to the V110 (again a little more control).

Most important this is what I experienced. Short story - forget specs and just listen.
George, I would respectfully, but very strongly, disagree with the notion that specs, and a good understanding of them, are useless.

Yes, specs will generally provide little if any insight into how a component will sound. And I certainly agree that "buying based on specs" is almost certain to result in expensive mistakes.

However, I doubt that any serious audiophile having even a tiny modicum of experience "buys based on specs." Although those who express disdain for specs commonly seem to make the IMO false assumption that those who consider specs to provide value do buy in that manner.

The very considerable value specs can provide, as I see it, is that when purchase decisions are being made they allow candidates to be RULED OUT, on the basis that they would be poor matches with either other components in the system (e.g. impedance incompatibilities, gain and sensitivity mismatches, etc.), or with the listener's requirements (e.g., dynamic range and maximum volume capability).

Without taking advantage of those kinds of benefits that can be provided by specs (and a good understanding of them), the randomness of the component selection process increases greatly. As does the likelihood of expensive mistakes.

Regards,
-- Al
Thank you Bombaywalla. Thanks also to Al and Ralph.
Agree with Al's last post. Stats, IMO, while not controlling factors, are nonetheless relevant and informative.

As I posted some time ago, I rued matching my ARC tube amp with my Paradigm Sig 8 v3 speakers. The S8s looked like the most tube unfriendly speakers one would want to match with a tube amp. And the truth be told, a Paradigm tech person strongly advised that the S8s should be driven with a high current/high power SS amp. Oooopps.

What confounded me was why my ARC VS-115 tube amp seemed to do a pretty good job driving the S8s even though on paper one might think otherwise. Well, it may still be the case that a high power/high current SS amp very well may be a better match with my S8s.

But then again, after a ba-zillion on line and off line messages with Al and Ralph I finally started to understand why my ARC amp did a good job with the S8s. There's a very important stat that I overlooked -- my amp's output impedance. Al and Ralph had to use a carbide steel drill bit before I finally got it in my head that a tube amp with "relatively" low output impedance and moderate negative feedback might perform somewhat like a Voltage Paradigm amp -- that is a SS amp.

In fact, ARC's literature reports, as confirmed by John Atkinson and Soundstage magazine, that the output voltage regulation of my old VS-115 and current Ref 150 off the 4 ohm taps is +/- .4 or .5 db regardless of speaker impedance and frequency. In addition, the damping factor of both amps, while not 1000:1, is still respectable. And that folks is why my ARC tube amps are able to do a credible job driving my "tube unfriendly" S8s.

Does that mean I should forego live auditions?? No. Does that mean stats tell me everything? No. But as Al just said above, if I have an interest in road testing a tube amp that performs like a Voltage Paradigm amp with a so called "tube unfriendly" speaker I should still give it a whirl (audition). I might be pleasantly surprised. And I have been!

So IMO a basic understanding of stats does have some benefit and informative value.

Thanks again Al and Ralph.

Bruce

P.S. I have a passing interest in checking out the Revel Studio 2 speakers. Revel's sales literature and member comments both state that the Studio 2s will sound best when driven by a high power SS amp. That sounds familiar. But I think Al might say don't automatically rule out trying the Studio 2s with my ARC tube gear. One day I just might!
Hi Al
I wrote that specs are useless because I've seen too many people refuse to even listen to some equipment based on specs alone. I'll admit when starting out I was one of them. I found that I believed specs more than my ears. Later I used my ears. I will admit the only specs that are meaningful would be input and output impedance matching of sources - pre - and amps along with capacitance and inductance of cables. But as far as power and THD a lot of those specs don't necessarily mean more power or a lower THD will sound better especially with your equipment. I'll use my Dyn - Bryston/Octave example. Dyn states my C1's need 180W or more to sound best. The Bryston B100 had 180W (test sheet showed over 200w @ 4 ohms) and the Octave V70SE has 70W at 4ohm. As good as the Bryston was it wasn't until I had an in home demo of the V70 that made me realize that V70 sounded more powerful and has more 'control' over the music.

Bryston has THD+noise:<0.005% 20 to 20khz at 100w into 8 ohms

Octave V70se THD < 0,1% @ 10 Watt into 4 Ohms

Based on those specs one would think the Bryston is a lot better for the Dyn C1's. Honestly it isn't even close. The Octave is a whole lot better which is a reason I stated specs are useless.

George
Thanks, Bruce. Yes, looking at JA's measurements of the Revel Ultima Studio 2 and your Ref150, it strikes me as a reasonable possibility that they would be a suitable pairing, using the 4 ohm tap.

George, I see your point. But I doubt that there are very many serious audiophiles who would either choose or reject an amplifier based on THD numbers, which are among the most useless audio-related specs I can think of. But even those numbers can be useful. I would be very hesitant to buy an amplifier having exceptionally LOW ("good") THD numbers, because that would probably signify heavy-handed application of feedback in the design. The probable consequences being sloppy performance on fast transients, and increased amounts of distortion components that are particularly offensive.

As far as power is concerned, yes, which of two amplifiers will "sound" more powerful has to do with dynamics, distortion characteristics, power supply quality, and other factors that don't have much correlation with the number of watts they can produce. However, to produce a given desired maximum volume level at a given listening distance, with a speaker having a given efficiency and given dispersion characteristics, requires a certain minimum number of watts. If the amplifier is substantially underpowered relative to that number, it suggests caution or rejection. If the amplifier is way over-powered relative to that number, it suggests that its gain should be looked into, because it raises the possibility that gain may be high enough to necessitate using the volume control at settings that are undesirably low.

So even those numbers can have their usefulness in some circumstances.

Regards,
-- Al
Great Thread Kelpie! Fact for any thread that garnishes response from the likes of AL, Ralph, Bruce, Zd.

It is Al's position on specs that drives my quest for understanding.
Here is a link that might help some with this equipment matching issue: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

Al is correct- THD is the sort of thing that may well have a reverse correlation with listening experience and for the reason he mentioned. I'm not a fan of *high* THD either, as the ear will convert the experience of distortion into one of tonality (odd orders contribute to brightness, the 2nd harmonic contributing to lushness). If distortion is present, detail can be obscured by the ear's masking principle.

The bottom line here is understanding how the ear perceives sound, and working with those rules rather than against them with the audio equipment design. Because designers frequently do not understand the way the ear hears things, we often wind up with spec sheets that don't seem to tell us anything about how the equipment sounds, even though that is what the spec sheet really should do.

In short, as an industry we often measure things that are not important (and place excess value on those measurements) while at the same time not measuring the things that **are** important (and placing no value on them at all...). Hence we still have to audition audio equipment.
Mesch,

Thanks. I would have written more but I would be just repeating what Al and some of the other posters said.

Bifwynne

"P.S. I have a passing interest in checking out the Revel Studio 2 speakers. Revel's sales literature and member comments both state that the Studio 2s will sound best when driven by a high power SS amp. That sounds familiar. But I think Al might say don't automatically rule out trying the Studio 2s with my ARC tube gear. One day I just might!"

Don't forget that Revel is a Harmon company just like ML. I'm pretty sure every dealer sells both brands. Its a good combo, but I wouldn't hesitate to try some other brands with Revel; tube or SS.
thanks a lot everyone and the gurus in particular. I love the combination of logic, science, opinion, taste and lack of hesitation to state one's preference without offence to anyone - this unique pot pourri seems to be an exclusive of audiophiles. . . nice to be one!