[Jibara]

Hello Adrian,

 

I am sorry if it came across as being defensive because it was not intended that way because I have every confidence in the products.  We have roughly 150 engineers at the main facility not counting the engineering staff we have here in the US and we have been designing, engineering and manufacturing products for a large number of the esoteric audio companies for over a decade now.  So the amplifiers have a long proven track record under various names.  I myself have been designing amps for over 25 years and if the amp will produce a certain amount of power at a given load impedance, then the current is a byproduct of the power. 

 

I started the thread to try and find out why people are asking for current ratings.  You see from my standpoint it doesn?t have any relevance.  If an amp produces a certain amount of power then it has to produce a certain amount of current or it wouldn?t make the power, they both walk hand in hand.  Thus if a company is truthful about the power ratings, the current will always be there.  So I honestly didn?t understand what the deal was and if people consider it to be important, then what measurements did they want (i.e. let me know the conditions and I can tell you exactly what it will do).  Unfortunately the thread took off in so many directions that it lost all focus and I still don?t have any more information than I did from the beginning.

 

Lonnie Vaughn

General Manager

Emotiva Audio

131 South East Parkway Court

Franklin TN, 37064

615-790-6754

[*Scotty*]

Jibara,people are looking for marketing claims regarding current from you so that they can compare claims from other companies.
For myself I look for an amplifier that will at least double it's 8ohm rms power output into 4ohms as this tells me something about the power supply capabilities of the amp.
Scotty

[JoshK]

I am confused.  You address this Adrian.  Are you reposting a private email to us and asking us if what is said is correct?  It would have been nice for you to preface it as such.

I do hope you aren't bringing an argument from another thread over here.  I will assume you are not.  If this is an argument from elsewhere you can pm me and I'll move to thread to the trash, as we have a no dirty laundry policy here.

OK, enough about housecleaning.  It does seem that the response about current delivery is correct.  If the power was stated at different impedances, like 8 ohm, 4 ohm and 2 ohm then you can get a sense of how much current it can deliver.  Its true that X watts is Y volts rms into a 8 ohm load, but that doesn't quite paint the whole picture as the test conditions are generally a 8 ohm resistive load, not the 8 ohm reactive load of most speakers. 

Why people ask about current, is a hand-waving way of asking about if it can deliver the stated power into a reactive load and/or a varying impedance load. 

The way I look at power, power is often stated as a 1 dimensional statistic X watts at 8 ohms and sometimes(often) also stated at 4 ohms.  This is a two point approximation of 2 dimensions.  The problem of power into a speaker is more of a 3 dimensional problem.  Power by impedance by frequency (usually only stated/tested at 1khz where speakers are typically their most benign). 

If the speaker halves in the midbass, as some commercially exalted speakers do, then some amps will clip seemingly short of their rated power if the power supply isn't capable of delivering the necessary increase in current demanded.

[planet10]

Its true that X watts is Y volts rms into a 8 ohm load, but that doesn't quite paint the whole picture as the test conditions are generally a 8 ohm resistive load, not the 8 ohm reactive load of most speakers. 

This is the crux of the question.

Power is voltage x current x cos(phase angle)

If you have a constant voltage amp then the more reactive the speaker then the more current the amplifier has to deliver to produce the same power-- to the point where phase angle is 90 degrees and the amplifier can not deliver any power.

Lonnie, if your amplifier can only deliver sufficient current to meet its rating into a resistive load than it will not meet that rating into a real loudspeaker.

dave

[Jibara]

Josh

Please move this thread to the trash bin and I rework my question. Thanks Adrian.

I apologize for not doing a lead in to the post. I came here for help as to the correctness of the email that was sent to me (Adrian). It is from someone I am considering doing business with and I just wanted to know if what I was being told was correct.

If that is dirty laundry than again I apologize but if I can't come here for answers where would you direct me to.

And thanks for the answers.

Regards
Adrian

[Jibara]

So then does maximum peak and maximum continuous current ability mean anything when judging a power amplifier?

[planet10]

So then does maximum peak and maximum continuous current ability mean anything when judging a power amplifier?

Yes. Understanding what they mean isn't necessarily straight-forward thou.

And since that current delivery costs money (bigger power supply, higher packaging & shipping costs...) best is the one that balances with the speakers you will be using them with.

dave

[turkey]

The way I look at power, power is often stated as a 1 dimensional statistic X watts at 8 ohms and sometimes(often) also stated at 4 ohms.  This is a two point approximation of 2 dimensions.  The problem of power into a speaker is more of a 3 dimensional problem.  Power by impedance by frequency (usually only stated/tested at 1khz where speakers are typically their most benign). 

The PowerCube test used by Peter Aczel gives a more 3D view of what an amp can do. It isn't perfect, but it's certainly better than the "200W into 8 ohms" that is all that many manufacturers give you for specs.


From one of his reviews:

"I began with our specialty, the PowerCube test, which is best performed with two simultaneously driven channels, although the readout shows only one channel. As I?ve explained many times before, the PowerCube test measures the ability of an amplifier to drive widely fluctuating load impedances. As far as I know, The Audio Critic is the only American audio journal to publish PowerCube measurements. The instrument for the test is made in Sweden; it produces repeated 1 kHz tone bursts of 20 ms duration into 20 different complex load impedances across the amplifier (magnitudes of 8Ω/4Ω/2Ω/1Ω and phase angles of ?60?/?30?/0?/+30?/+60?). The graphic output of the instrument shows the 20 data points, at 1% THD, connected to form a more or less cubelike polyhedron. The test shows up the differences between otherwise similar amplifiers when it comes to real-world loudspeaker loads rather than just resistances. "

[JoshK]

Josh

Please move this thread to the trash bin and I rework my question. Thanks Adrian.

I apologize for not doing a lead in to the post. I came here for help as to the correctness of the email that was sent to me (Adrian). It is from someone I am considering doing business with and I just wanted to know if what I was being told was correct.

If that is dirty laundry than again I apologize but if I can't come here for answers where would you direct me to.

And thanks for the answers.

Regards
Adrian

Its ok, we understand now.  At first, I thought you were bringing a reply in private to a mudslinging that went on somewhere else and I didn't want it to spill over here.  Its fine, carry on.

[JoshK]

Its true that X watts is Y volts rms into a 8 ohm load, but that doesn't quite paint the whole picture as the test conditions are generally a 8 ohm resistive load, not the 8 ohm reactive load of most speakers. 

This is the crux of the question.

Power is voltage x current x cos(phase angle)

If you have a constant voltage amp then the more reactive the speaker then the more current the amplifier has to deliver to produce the same power-- to the point where phase angle is 90 degrees and the amplifier can not deliver any power.

Lonnie, if your amplifier can only deliver sufficient current to meet its rating into a resistive load than it will not meet that rating into a real loudspeaker.

dave

Yeah, forgot about the phase angle.  4 dimensions. 

[Occam]

......
For myself I look for an amplifier that will at least double it's 8ohm rms power output into 4ohms as this tells me something about the power supply capabilities of the amp.
Scotty

If it more than doubles, its telling you more about the amplifier topology.
But we all enjoy a bit of engineering humor. 

-Paul

[planet10]

The PowerCube test

Can you post a picture of the graphic generated? This sounds like a useful test.

dave

[turkey]

The PowerCube test

Can you post a picture of the graphic generated? This sounds like a useful test.

dave

Here's one from his review of the Amplifier Technologies AT6012:





There's also an even nicer-looking one in his review of the Parasound Halo A 21:

http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=18&blogId=1

[turkey]

Here's the company that makes the test equipment:

http://www.audiograph.se/

[turkey]

Here's the company that makes the test equipment:

http://www.audiograph.se/

Wow, that Rockford-Fosgate car amp sure is a monster. I don't see why anyone would buy one, but it's impressive to look at.


http://www.rockfordfosgate.com/products/product_details.asp?item_id=105829&locale=en_US

http://www.audiograph.se/press/rockford/index.htm

[JoshK]

Those Parasound measurements look fantastic till you get to Figure 4.  I'd like to see the FFT at 1w and say 10w. Note how THD+N goes down until 5-10w, then back up gradually, typical of an amp with lots of feedback.

I am not trashing this amp.  But to my eyes the Fig 4 looks pretty ugly, exactly what the low power crowd tries to avoid.  However, almost no listening is done at 250w unless you are driving Maggies, Apogees or B&W 801s.

[planet10]

Thanx Turkey

dave

[turkey]

Those Parasound measurements look fantastic till you get to Figure 4.  I'd like to see the FFT at 1w and say 10w. Note how THD+N goes down until 5-10w, then back up gradually, typical of an amp with lots of feedback.

I am not trashing this amp.  But to my eyes the Fig 4 looks pretty ugly, exactly what the low power crowd tries to avoid.  However, almost no listening is done at 250w unless you are driving Maggies, Apogees or B&W 801s.

The low power crowd often seems to throw out the baby with the bathwater.

It doesn't look to me like there is anything in Fig 3 or 4 that would be audible. Plus, amps used by the low power crowd will likely display more distortion during normal use than this Parasound will.

[JoshK]

I guess that is the $64,000 question.  I'd rather not turn this into a camp 1 vs camp 2 debate.  However, on the question of audibility, I would tend to disagree. Higher harmonics are much more easily heard.  I'd choose higher THD if it were made up of 2nd and 3rd over low THD with a profile like Fig 4.

[peranders]

Jibara, a friendly note, don't publish private emails without asking the writer first. Even if the message was harmless I think you should ask first. I don't think you would like your emails published without your knowledge.

BTW: My personal view is that the amp should be able to deliver plenty of power into complex loads.