[waltj2k]

In a conversation with Klaus he mentioned that I should pay more attention to current than wattage. Why is this important?

Walt

[speedcenter]

let me add something to this - 'cause some folks on another forum feel that Klaus is padding the current output numbers.

check here
http://www.audioasylum.com/forums/MUG/messages/43370.html

this is the basic argument:

Let me repeat what I said before:
Odyssey's current output claims are wildly overstated.


Now, let me ask you what kind of power outlets you will have your amps hooked into? Don't tell me 15A or 20A circuits, or I'll be forced to snicker.

In order to actually deliver 240A you would need at least five 50A circuits to power those amplifiers. If you live in the US you most likely have (at best) 200A electrical service to your house, so where exactly would all that current come from?

Lastly = 240A is about 27,000 (twenty-seven THOUSAND) Watts. Is that what they're rated for?

The laws of physics cannot be bypassed, even by high end audio gear.

It is my understanding that these current values aren't "constant" and have something to do with the memory in the capacitors of the amps. Anyway - is there some sort of standard to measure this or a formula?

[W.C.]

You would be surprised at how little wattage you actually use listening to music or H/T.  Alot also depends on the sensitivity of your speakers. High current provides more CONTROL over the speakers

[speedcenter]

as far as wattage used on the speakers I have and the people who frequent the forum where the Odyssey current delivery claims were challenged - Magnepan stands for "inefficient"

It takes me about 30 minutes of listening at moderately loud levels to get my monos nice and hot...  Maggies dip well below 2 ohms at some frequencies, so the amp does get a real workout. Does that mean I use more "wattage"? Dunno - all I know is that the monos are the first amps that can actually deal with my speakers without running out of steam.

Peter

[W.C.]

The impedance of my Kappa 9's dip down to .7 ohms in two places throughout the frequency range. These speakers are known as amp killers. The Odyssey Mono's handle them with ease. The high current is what  really makes them sing.

[Eduardo AAVM]

Well I just can say that here in Mexico for a review in a magazine, the Stratos 120 was tested with a pair of Apogee Centaur Major, these are some quotes from that review:

"It (Stratos 120) worked excellent with speakers (Apogee Centaur Major) which their nominal impedance can get below of 2 Ohms"

"this amplifier drove them with authority and dinamicly"

"it never sounded fatiguing"

"on might think that it's 150W per channel are something more than that"

One final quote:

"In conclusion, it is an amplifier, one of the really few ones that one can play any kind of music without restrictions or limitations"


And it was printed that way...



So I do not if the numbers but the facts are like this...

[doug s.]

my electrocompaniet aw60ftt's, (currently listed here f/s, btw, hint-hint!  ), tho only rated at 60wpc into 8 ohms, are also rated at 60 amps current output, & are stable into loads <0.5 ohms.  they will drive *anything*!  

so, why am i selling?  well, i finally found an old aw75, to match the one i've owned since ~'95, so i still have a matched pair, & i wanna try some serious toob amps, now that i've gotten a taste of toobs, w/these modded wave-8's i picked up..

doug s.

[klaus@odyssey]

Yep,  there's the guy over at AA who's trying to rip us one.  What else is new ???  Funny that the only responses he's ever made were directed towards us.  Also,  I tried to check on his info,  and he's been deleted by AA.  ???????

Yep,  he has a calculator,  alright,  and knows how to use it.  Big deal.
For one,  the current is always a total for both chjannels,  and it's the absolute max that the amps are capable of,  for a short period of time.  Reality is that no amp will sustain it's maximum current delivery for a longer time period.  

Also,  all depends on the speakers,  what they demand from the amp.  There are wattage demanding speakers, (usually with a bit higher efficiency)  and then there are more current demanding speakers,  such as planars etc.

hehehe,  as for claims,  just look at those of class whatever digital amps and some other manufacturer out there.  Makes the Stratos look like a dwarf.   As for lethal amps,  yep.  Just ask Marbles.  If you want to get serious about power supplies,  take one of the Kraft 400's,  run it up full tilt,  and hook some welding equipment to it.  all possible.

Anyway,  the fact is that the Stratos is a high current design,  and that it runs even very difficult loads.  End of story.

Klaus

[jcoat007]

I love Klaus' response.  

Shut up
Sit down
and
Hold On

BAM!!!!

Next question???

[nathanm]

...without running out of steam.

I hear this type of comment a lot and I'm curious as to what people think it means.  (Obviously it's just a figure of speech, as the Lirpa turntable is the only steam-powered component out there) When one says "runs out of steam" what does that translate to?  How would you describe what you're hearing when you say the amp ran out of steam?  Just curious.

[Tyson]

dynamics get compressed and soundstage tends to collapse.

[Dunedain]

Very interesting discussion.

It was always my understanding that the amount of watts
that were available were what determined how many db could
be delivered from a pair of speakers (assuming the speakers
were capable of playing at the volumes the amp could deliver).

So while current no doubt is very important to amp performance,
can it also replace output in watts to some extent?

For example, lets say you have a pair of main speakers that you
want to use for watching movies on DVD.  And you want to watch
the movies, at least some times, at full Dolby Digital reference
volume levels.  If I recall correctly, DD reference volume
specifies 105 db for max SPL (not counting low frequency effects)
for sound during the movie.  So, if you have speakers of a given
sensitivity and you want full DD reference volume at your listening
position, you will need a certain amount of watts in order to be
able to do that.  I've been operating under the assumption that this
watt figure was non-negotiable in terms of achieving a given SPL at
a given distance with speakers of a given sensitivity.  But perhaps
current comes into play here, as well?

Now, let's suppose that you have an amp that cannot meet the watt
requirements for reaching this reference SPL at the distance
required with your speakers.  But the amp has superb current
capabilities, something like the DM Stratos, for example.  Let's
further suppose that the amp falls, say, 75 watts short of what
on paper would be required to get to that target reference SPL,
according to the standard formula.  Could the amp's tremendous
current prowess overcome that 75 watt shortfall and still deliver
the reference SPL level at the listening position (let's assume for
the sake of the discussion that the watts needed at reference SPL would
be required for a longer period of time than the amp's capacitors
could cover in a temporary surge of peak watt output)?

[Dunedain]

Any thoughts, comments, ideas or theories on this?
Trying to figure out what all this debate over
watts and current is about.  

[W.C.]

I think the bottom line is that if you want to watch your movies at full dolby digital reference levels, you're going to be needing a hearing aid in the not too distant future!

[klaus@odyssey]

Well,  yes, thta's quite possible that great current reserves can overcome shortages in wattage,  as there are so many different factors involved here,  such as stability of an amp at certain loads, real efficiency on the wattage,  etc.

I don't think that any of the "established" or non-established formulas really work 100 % in any case in the real world.  There are so many system combinations out there that on paper / formulas  don't have a chance,  and yet,  they do work.    Of course,  I'm not talking about a 3 watt triode here at Maggies 3.6's in a HT setup.  So, no,  I don't subscribe to hardly any of the engineering approaches.  HOWEVER<  the single most important issue here is indeed the speaker.  Does it require more wattage from an amp,  or is it more a current demanding unit ???  Thus, with the great variety of speakers out there,  one has to know first what one should look for in an amp.

Then there's the pitfall of specs, (hehehe,  again).  It's really funny.  Most of the times we're accused of having a whimpy amp,  hehehe   However,  lately we're also accused of vastly overstating and making up specs as well.  

Ultimately,  when you're talking 105 dB plus or whatever the speaker can give you before breaking up, then don't look at the wattage but the real stability of a given load at 90 % full power constantly for several hours.  Unfortunately,  no manufacturer will post this spec (whyshould anybody ?),  and I guarantee you most have not done this test anyway.  

As for the Startos,  we're talking 90 % load at 1 Ohm for 2 hours.  Done.  Measured close to 400 W.  with 300 + W. per channel / one channel driven.

Yep,  you could fry eggs on the sucker after a couple of hours,  but man,  stbile, hehehe.

Late

[mgalusha]

To add a little to what Klaus said. There are formulas for determining the power needed for a certain spl and how fast the spl drops off vs distance from the speakers. The problem is that in a real listening room things don't always work out exactly as theory dictates...

Here is a little of the theory.

• Watts = I x V where I is current and V is voltage. This is a standard electrical formula.



• Each 3db increase in level requires a 100% increase in power. Example: A speaker  with an 8R impedance produces 87db @ 1 watt. It will require 2 watts for 90db, 4 watts for 93db etc.



• SPL drops off 6db for each doubling of distance. Example: A speaker is producing 97db @ 1 meter. If your listenig position is at 4 meters theory says that the SPL will be 85db. In the real world this doesn't happen due to reflections and room interactions. Also, line array's and planar speakers drop off at a different rate.



• You gain 3db when two speakers are playing. So if each speaker is producing 97db you would have a 100db source.



• Speakers are rarely resistive loads and their impedance changes with frequency. It's not uncommon for speakers to drop into the 2R range at low frequencies

Lets take a few of these items an combine them into an example. You mentioned 105db peak SPL. If you have fairly efficient speakers of 90db/1W/1Meter theory says that for 105db 32Watts would be required. This is for 1 speaker at 1 meter with a perfect 8R load. If the listening position is 4 meters the level would be up to 12db lower. (in theory)

Since there are two speakers we can subtract 3db from what is needed because they add. So we would need 114db at the speakers for 105db at the listening position. Again this would be in an anechoic space with theoretical losses.

To produce 114db from a speaker with 90db efficiency would require 256 watts per channel.

Since Watts = I x V and ohms law shows that I = V/R then as R (impedance) drops the current requirements will go up. In our example 256 Watts into an 8R requires 45.2V and 5.6A. If the impedance of the speaker drops to 4R the voltage requirement remains the same but the current has to double. This would be 11.3A / 512W. At 2R it doubles again - 22.6A / 1024W. (still at 45.2V)

This is of course theoretical. Usually there is not nearly as much room loss as predicted but many speakers are not well behaved. Some, like Apogee ribbons can drop to 1 ohm and most amplifiers don't like that type of load.

Looking at the above current requirements it seems that if an amplifier could produce 25A of current it would drive most any speaker to high levels. It probably would. Why then are high current amplifiers (such as the Stratos) popular? In my experiance this translates into dynamics and a sense of ease.

If the amp is capable of high currnet there is usually the feeling of reduced strain and unrestrained dynamics. My speakers are a good example. I have a pair of Vandersteen 3A's. Vandersteen specifies an amplifer of 100 - 200 WPC for these speakers, I think this is an underestimate. While I have always enjoyed the sound of these speakers they were not as dynamic as some others; this was a tradeoff I was willing to live with. Once the xtreme mono's arrived the dynamics of these speakers were transformed.

As Klaus mentions it's how the speaker interacts with the amp. In theory I only need a 100WPC receiver, in reality the more powerful of amp I have used, the better they system sounds - at most any volume level. I have some 100WPC tube amps. They sound very nice but lack the dynamics and control of the xtremes. Will they play loud, sure but does the system have a "live" sound? Nope. It's much more alive with the big amps in the system.

Hope this is coherent, it's a little early for a long post.

Mike

[Dunedain]

Thanks for the replies.

Great posts, Klaus and Mike!  I didn't know that you got an automatic 3dB boost
just from having the second speaker.  That makes sense, though, just like subwoofers
reinforce each other when co-located in a corner of a room.

That's quite an impressive torture test you ran your amp through there, Klaus.
You mentioned a Stratos amp, which model were you referring to?

So, current can overcome what at first glance might appear to be a shortfall of watts
on paper.  *Very* interesting.  As usual, the theories are just that, in practice things
tend to work a bit differently.  And, of course, we weren't even factoring in the
capacitors, but rather continuous power was the focus.  And since all the Stratos amps
have hefty stored up reserves in their capacitors, that further enhances what they can
do when something like a big 105dB spike is called for during an explosion in a DVD movie.

Klaus, these large uF capacitance figures listed for your various Stratos amps, is
there some sort of rough formula that would indicate how much of a boost in watt output
they could provide temporarily for a given amount of uF?  For example, 60,000 uF = about
100 watts above the amps rated continuous watt output, 120,000 uF = about 200 watts for peak
watts above rated continuous output?

Thanks for any info.!  

[speedcenter]

You mentioned a Stratos amp, which model were you referring to?

I think it was the "Stratos Frying Pan / Griddle Edition" - upcoming product just for the kitchen. Finally an amp the wife will accept!