High Current Amp Benefits?

[Sarius]

Hi,

I've been noticing that some amplifiers are advertising themselves as 'High Current' and I was wondering what the benefits are?

For example, I'm looking at two stereo amps, at 8 Ω one is 120 watts/Ch, the other is 150, which is a trivial difference. However, one claims 20 amps of current delivery, the other 45.

Given that doubling the power only gives a 3 Db difference in volume, it would seem that there would be less than a Db difference in potential headroom. I was wondering what improvments the more than doubling of the current might imply?

Thanks

 

[mike c]

not exactly your question, but pretty related: it's a sticky on top of the amps and receivers sub forum ...

http://forums.audioholics.com/forums/showthread.php?t=14280

 

[Pyrrho]

The claim of "high amperage" or "high current" can be made about any product; it means absolutely nothing. As for the specific ratings, are you talking about instantaneous amperage, or continuous, or something else? Without that information, even the numbers are meaningless. What you are looking at really is marketing, and it sounds like they are playing games with you. Basically, you should look for continuous power output RMS into whatever impedance you are interested in (8 ohms, 4 ohms, etc.), at an acceptable level of THD (Total Harmonic Distortion), from 20 to 20kHz (or a wider frequency range). That will tell you what you need to know about its output.

 

[Sarius]

not exactly your question, but pretty related: it's a sticky on top of the amps and receivers sub forum ...

http://forums.audioholics.com/forums/showthread.php?t=14280

I found it more confusing than enlightening as I attempted to wade through it. I am talking about stereo amps for use in music only, not receivers. I'm more trying just to understand why I might wish to spend more on an amp that offers 'higher current', as in double the current when the wattage per channel is about the same. I'm not that iinterested in in decrying something as hype, rather I'd like to assume that we actually have two amps with close power ratings with one amp having double the 'drive current' (whatever that means) than the other, and understand what the benefits, if any, might be in terms of my musical enjoyment.

Thas is, I guess my question is will there be more of some sort of musical goodness when a higher current amp is driving a system as opposed to a lower current one? With current is there some optimum amount for a given power, or is it the case that more is 'better'? What are the supposed benefits in having a higher current amp driving your system and why are they supposed to occur?

Inquiring minds want to know

 

[MDS]

Voltage, current, impedance, power, etc are all related by Ohm's Law. The amp needs to be able to supply the required amount of current in order to meet its stated power rating into a given impedance. If it can do what it claims, then the current is 'high enough'. That is why 'high current' is more a marketing term than any indication of quallity.

 

[j_garcia]

Put it this way, you don't want a low current amp do you? What MDS said - when people got immune to every receiver claiming to have 100wpc and many not being able to actually deliver, they started throwing around "high current" a bit too much to the point where it is sort of losing it's meaning.

 

[Hi Ho]

Unless you have your amplifier plugged into a 40 AMP circuit, it couldn't possibly deliver 40 amps. A standard household circuit is 15 AMPS, some 20 AMPS.

 

[Dan Banquer]

High Current

Some of you may wish to read this article and be better informed.
http://www.audioholics.com/techtips/audioprinciples/amplifiers/HighCurrentAmps.php

d.b.

 

[PENG]

Unless you have your amplifier plugged into a 40 AMP circuit, it couldn't possibly deliver 40 amps. A standard household circuit is 15 AMPS, some 20 AMPS.

Don't forget amps specify their high current capability in terms of instantaneous, and at the output not input. A 15 amp circuit handles 15 amps at 120V, that can translate into much higher current at the amp's output side where the voltage is lower. Example: 15A at 120V will get you 30A at the secondary side of the transformer if the voltage is stepped down to 60V.

 

[Sarius]

Some of you may wish to read this article and be better informed.
http://www.audioholics.com/techtips/audioprinciples/amplifiers/HighCurrentAmps.php

d.b.

Thanks, it was a truly lovely and informative article as far as it went. The issue being that it didn't go far enough to answer my question.

Based on your information and other reading I've been doing, I'll attempt to clearly lay out both what I'm after and what I've found to date in the hope that you more knowledgeable folks can extend or correct it.

First the goal we're after. My understanding is that a preamp puts out a signal that essentially consists of a varying voltage and the job of the amplifier is to amplify that signal to a level that will adequately drive the speakers. The ideal is the so-called 'straight wire with gain' in which there is a linear relationship between the preamp's voltage output and the amp's voltage output. If that relationship become nonlinear, it's considered 'Bad'.

Now, avoiding 'Bad' is complicated by the fact that a speakers impedance varies with frequency, and can vary quite a bit. For example, looking at the curves for the EPOS M5, it bounces between about 4 Ω and 12-14 Ω three times over its range.

The Theil CS 2.3, the next generation of a speaker I happen to own, goes from 2 Ω at 450 hz to over 20 Ω at 20 hz. Given that the speaker is seeing a composite signal which is rapidly varying, it can see a very rapid, dare we call it 'instantaneous' change in the impedance load it presents to the amp. If the amp can't adapt fast enough to this changing load, then I would assume that the effect would be some sort of nonlinearity in the output, which we have defined as 'Bad'.

So, how might this relate to the current. Let's stay with the published specs of the Theil. It is rated at an output sensitivity of 87 db/watt. Let's assume one is listening at an average level of 80 db to material where the most dynamic passages could hit 114 db. Given that a Redbook CD has a possible dynamic range of 96 db or more, assuming a 34 db jump to the maximum transient seems reasonable.

OK.. let's see what we need to service such a transient peak. First, if one watt is giving us 87 db, how many watts will we need to get 114. Now we know that doubling of the power gives us 3 db more volume, so it's pretty easy to determine that we'd need 512 watts, at least for a few milliseconds to properly service that peak.

Assuming that our amp is up to the task, what current would be needed? Mr. Banquer tells us that:

Power = Current squared times the resistance.
So.....

Current = The SquareRoot of (Power divided by Resistance.)

Now looking at that equation we see that the lower the Resistance, the greater the current that would be required. So, for the Theil, the lowest impedance we see is 2 Ω, so if we substitute 2 Ω and 512 Watts into the equation and solve for Current, we find that we'd need a maximum of 16 amps to maintain the signal under the worst case.

Ah Ha! But, my experience has been that electronic circuits tend to become nonlinear at their extremes, and as we said, nonlinear is 'Bad'. Back when I was involved in precision measurements, I found that keeping my signal generating and measurement devices working at about the middle of their potential ranges give, all around the best results. So, if I applied that here, I would be looking for an amp that had an 'instantaneous' current capacity of about 30 amps to meet the stated requirements with these speakers.

So, I conclude that there is some value in knowing the Instantaneous Current, and it has an effect. I would conclude that of the two amps I mentioned in my initial posting, the 20 amp-amp is probably too light to be a good match with my Theil CS 2.2's (assuming that they have a similar impedance curve to the 2.3's), and that the 40 amp-amp would be ample

I invite informed comments.

 

[EdS]

You make a good case why you need a max current of 16A to drive your speakers to 512W, and that you would want an amp capable of 30A so that you are not driving your amp to it's extremes.

However, at least when discussing some of the brands that rate their receivers/amps as "High Instantaneous Current", I don't see the conditions under which the measurement is made. In other words, when an amp is rated at 40A High Instantaneous Current", what is the impedance that is being driven, what is the time duration, single channel/all channels, etc. Without that information the claim does not mean very much.

Some receivers (Yamaha is at least one, I know there are others) rate their max IHF output into a variety of loads. I believe that the IHF measurement is a 10% duty cyle, something like 100ms on / 900 ms off. I don't know if that is truly representative of typical music duty cycle, but at least you do know the parameters of the measurement.

 

[Dan Banquer]

High Current

"So, I conclude that there is some value in knowing the Instantaneous Current, and it has an effect. I would conclude that of the two amps I mentioned in my initial posting, the 20 amp-amp is probably too light to be a good match with my Theil CS 2.2's (assuming that they have a similar impedance curve to the 2.3's), and that the 40 amp-amp would be ample"
Are you trying to do sound reinforcement with an 87db spl speaker? If so then read on.
You will need an amp that will give you 200 to 250 watts rms into two ohms. If you understood the article then you will understand that the watts rms figures mean double that in peak power. BTW : for an SPL of 110db atthe speaker with an 87 db/spl speaker you will need a 200 watt peak from your amp.
I think you can do the math from there, the examples are in the article.
d.b.

 

[Sarius]

Let's see.......

This is more of a hypothetical question, I'm just attempting to understand what's going on here without reference to marketing and such. I would tend to assume that more specialized equipment such as two channel audio separates, as it is generally marketed to a more knowledgeable audience, would be a bit less fast and loose with their specs then the more mass market focused mid-end AV Receivers.

Of course, $2,000 cables are marketed to the same audience, so .....there you go..

I am not attempting to do 'sound reinforcement' (whatever that is). I am trying to understand what it takes to get the best possible sound, in terms of music reproduction, in my home and this was a sincere question. Through working through it, I've learned quite a bit. Not that I necessarily want to spend the money to tweak things to the nth degree, but to at least attempt to understand the tradeoffs that I'll be making if I chose not to.

This does seem to explain why people report more open highs and such when they go to honking big amps. I would imagine that things like cymbals might have very brief very high amplitude signals which a lower power amp might just nip the top off. If this was happening in fractions of a millisecond, you wouldn't actually hear it as clipping, but I think the loss would have a negative impact somehow. Being able to reproduce even those very brief bursts at 115 db (or whatever) accurately might be heard as 'more open' or 'transparent' or however the audiophiles enthuse over their sound.

I might mention that I have separate home theater and music rooms. I don't even have a TV in the music room- it's for stereo audio only, and (within limits) I'm trying to get the best sound that I can in it. Best defined as 'best for me' of course

In that room I'm only interested in amp/preamps or integrated amps, not receivers, and frankly I don't think one needs to hold HT receivers to the same standards. I dropped a Yamaha RX V2500 into my HT two years ago and couldn't be happier- in fact the last couple of times I went to an actual movie theater the sound was so disappointing compared to what I hear at home that I simply stopped going... no point. Frankly the picture is better at home too! However, except for background while reading, I don't seriously listen to music on that system.

 

[PENG]

Sarius, I think if you are aiming to hear 114 dB of low frequency stuff you do need a high power (high current) amp, especially if you listen to music without a subwoofer. Mid and high frequency material, on the other hand, do not need very high current/power. For example, a B&W800 can hanle up to 1000W of unclipped power but it's tweeter may not be able to handle much more than 30W continuous.

 

[Sarius]

Hi Peng,

I agree about needing the 'oomph' for low frequency and loud, but that's not what I was talking about. I think the need for high power (current?) capacity in the high frequencies has not been well addressed.

If you look at the equations, frequency doesn't enter into them at all. Thus, if you have a short sharp signal, like a cymbal, with a waveform that is very narrow, say a tenth of a millisecond, but very high amplitude, say 115 db or more, you'll still need 4-500 watts out of your amp to reproduce it correctly. Now granted, you won't need it for long, so issues like heat build up aren't a factor, but it seems to me that if your amp runs out of headroom, the very top of the wave will be nipped off. This won't sound like classic clipping, but I would guess that the electronics won't be happy, and the tweeters, being mechanical system will not enjoy attempting to reproduce a squarewave, even one that is only a small fraction of a millisecond wide. Won't hurt them, but they'd probably take a millisecond or so to settle back down which would tend to muddy the highs.

We've heard people claim that when they put very high power amps into their systems that it sounded better, even at reasonable listening levels. What I'm suggesting here is that there may be a good reason for it. That being that there may be more brief high amplitude transients in well recorded dynamic material than we realize which a lower power amp would fail to adequately reproduce leading to an slight muddiness in the sound. I'm suggesting that very short, sub-millisecond, high amplitude high frequency signals would not be heard as 'loud', but as the 'openness' and 'transparency' that audiophiles seem to prize.

So, the issues involved in attempting to blast the bass or listen at a very high overall volume, I think are fairly well understood. I'm attempting to explore the issues involved in choosing an amplifier for trying for the best sound at moderate levels and understanding why one might be interested in a higher power amp than, at first, one would think one needs.

 

[gmichael]

Hi,

I've been noticing that some amplifiers are advertising themselves as 'High Current' and I was wondering what the benefits are?

For example, I'm looking at two stereo amps, at 8 Ω one is 120 watts/Ch, the other is 150, which is a trivial difference. However, one claims 20 amps of current delivery, the other 45.

Given that doubling the power only gives a 3 Db difference in volume, it would seem that there would be less than a Db difference in potential headroom. I was wondering what improvments the more than doubling of the current might imply?

Thanks

Higher Amps help if you are driving low ohm speakers. When the ohms drop you need more Amps to equal the same wattage. So, say you start with 100 watts into 8 ohms drawing 10 Amps (not sure if you need 10 Amps but I'm in a hurry). Drop that to 2 ohms. Now you need 40 Amps to give you the same power or you speakers clip. And your amp may overheat trying to give you more than the 20 Amps it's rated at.
If you have 8 ohm speakers it shouldn't make any difference.

 

[PENG]

Hi Peng,

I agree about needing the 'oomph' for low frequency and loud, but that's not what I was talking about. I think the need for high power (current?) capacity in the high frequencies has not been well addressed.

If you look at the equations, frequency doesn't enter into them at all. Thus, if you have a short sharp signal, like a cymbal, with a waveform that is very narrow, say a tenth of a millisecond, but very high amplitude, say 115 db or more, you'll still need 4-500 watts out of your amp to reproduce it correctly.

You are right, I have not seen much written about high frequencies related issues neither. I think we need to first find out how loud is a short sharp cymbal signal at 115 dB? How would most human feel about a 4500 Hz signal that they are very sensitive to as compare to a 30 Hz signal that they are less sensitive to, given that both would register 115 dB? Let me spend some time on this and get back to you if I find anything meaningful.

Just read this from the B&W site:

"A typical music or speech signal has a complex energy-time characteristic; it contains many short-duration, but high level peaks which, although they contribute little to heating the voice coils of the drivers, still require the amplifier to be capable of delivering the required voltage without clipping. Obviously, an amplifier that can do this is also capable of delivering continuous tones that do contain high levels of energy that may damage the driver voice coils. This is especially true at high frequencies, where the relatively small tweeter cannot handle the same level of continuous power that the more rugged bass and midrange units can. In fact a typical continuous power rating for a tweeter might be 10 to 20 watts, yet it can be used in a complete speaker system having a power rating in the hundreds of watts – providing the signal is speech- or music-based."

So if you have a super higher power amp, sure it won't clip as easy, but you could still fry those little tweeters if you are not careful. If you are interested in reading the whole thing, follow this link:

http://www.bwspeakers.com/index.cfm/fuseaction/local.faq/ObjectID/F5CA2628-3D20-11D4-A67F00D0B7473B37

 

[PENG]

Power = Current squared times the resistance.
So.....

Current = The SquareRoot of (Power divided by Resistance.)

Sarius, those forumula are true for real power (common referred to in engineerng terms), i.e. power in watts. Some of the electrical components, e.g. the wires that feeds the outlet, have to deal with the total current, including currents that don't produce watts for you but simply magnetize the power transformer in order for it to do it's job of stepping voltage from one level to another. So in such calculations we should include the effect of power factor, the cosine of the phase angle between the voltage and current phasor (or vector, in physics terms). This could vary between 1, for pure resistive load, and almost 0 for inductive and capacitive load. Take a look of some Pioneer, Yamaha spec you will see that they specify their power consumption (not maximum) as 480W or 630VA. To calculate the current draw from the outlet the P.F. unknown, you have to use 630, not 480. That is, 630/120=5.25A. This is just an example, the same goes for the speaker, the current drawn by a speaker is not always in phase with the voltage. So while it is correct that Power in watts=Current (in amps) squared X resistance, the speaker usually draws more current than the value you calculated using this formula if you assume its impedance=resistance (which is usually not the case).

Everytime I see such posts I tried to resist pointing out the effects of the phase difference between V and I, because I thought it may seem trivial. I always ended up responding because I do think a 20% or higher error is not that insignificant for some electrical/electronic components.

 

[mtrycrafts]

Everytime I see such posts I tried to resist pointing out the effects of the phase difference between V and I, because I thought it may seem trivial. I always ended up responding because I do think a 20% or higher error is not that insignificant for some electrical/electronic components.

Speakers are usually less than 60 deg phase, either inductive or capacitive. How would that spec out? At least, David Rich uses that as the max phase when testing amps specs beyond resistance, how well it holds the rail voltage at those phases beyond resistive only.

 

[Dan Banquer]

High Current

If the issue is the amplifier and the AC line, then typical linear amps start out with a power factor of .65 and at higher power goes up to .8 or so. The measurements I have taken so far indicate that Class AB amps get more efficent at higher power levels.
d.b.