Ohm's law (V=I*R and W=V*I) is in operation here. Say a typical transistor amp is capable of delivering 25 volts into an 8 ohm load. That'd give 3.125 amps of current, which is about 80 watts.
Hook the same amp to a 4 ohm speaker and the current demand is now double at 6.25 amps needed. However, if the amp can't supply the extra oomph, they you have a current limited amp. If the amp can deliver the extra current, you now have a 160 watt amp into 4 ohms instead of an 80 watt amp.
Magnepan 1.2 and 1.6 speakers are 4 ohm units so will demand more current from a transistor amp than an 8 ohm speaker. Some transistor amps will be challenged by this and not respond well.
Most tube amps run their output tubes through a transformer that changes the output voltage to match the impedence of the speaker. The max current stays constant whether 4 or 8 ohms (assuming the output transformer has both taps) but the max voltage changes. An 80 watt tube amp will deliver the same watts & current to both a 4 ohm or 8 ohm speaker, but the 4 ohm speaker will get double the voltage. |
I found the explanation below on the B&K Website in their FAQ's and think it's good. (I copied it directly from their FAQ - so credit to B&K).
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Question: What is a high-current amplifier and why is it better?
A high-current amplifier is capable of delivering power into low impedance loads (speakers)
without going into protection and/or shutting down. Ideally, an amplifiers output power would double
every time the load presented at its output is halved. For example, an ideal amplifier rated 250
Watts @ 8 Ohms would deliver 500 Watts @ 4 Ohms, noting that the load has halved and the
power has doubled. In actuality, a real-world high-current amplifier capable of 250 Watts @ 8
Ohms might be delivering about 425 Watts @ 4 Ohms.
An easy way to identify a high-current amplifier for use with home consumer electronics is
to look at what happens to the power rating as the impedance of its load (speakers) drops. The
closer the amplifier comes to approaching the ideal amplifier scenario, the more current the
amplifier is capable of delivering and the better the sound reproduced by the speaker.
In a typical amplifier-speaker circuit, voltage and current are delivered to a very complex load
consisting of speaker drivers, resistors, inductors, and capacitors. Voltage may be thought of as the
potential to do work, and current as what actually flows to do the work. Although basic power may
be calculated by the simple multiplication of voltage and current, it is the delivery of the power from
the amplifier to the complex speaker load that accounts for why two amplifiers may have the same
power rating into identical impedances (speaker loads), but still be significantly different from one
another in sound quality. Some of these sound quality differences may include perceived loudness,
depth, and clarity. Amplifiers that are designed to operate with high voltage as opposed to high
current are typically much better suited to high impedance loads, typically 8 Ohms and higher.
Lower current rated amplifiers have been said to sound dynamically limited and harsh at high
listening levels.
High quality audiophile speakers can have nominal impedances from 8 2 Ohms, and
during very dynamic passages in source material can easily dip below 2 Ohms. These super low
impedance drops can easily choke a high voltage amplifier with limited power storage capacity. For
a high-voltage amplifier, this will likely cause problems and trigger its protection, not to mention the
less than nice sound it may produce. A high-current amplifier operates with much less effort and
typically does not have any problem with these types of speakers.
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The max current stays constant whether 4 or 8 ohms (assuming the output transformer has both taps) but the max voltage changes. An 80 watt tube amp will deliver the same watts & current to both a 4 ohm or 8 ohm speaker, but the 4 ohm speaker will get double the voltage. Not exactly, max power stays the same but both voltage and current change. The 4 ohm doesn't get double the voltage of the 8 ohm, that would produce 8 times the power. The 4 ohm gets .707 of the voltage that an 8 ohm speaker gets and draws 1.414 times more current. This keeps the power the same for both. |
Herman, thanks for the correction. Shows the perils of replying off the top of one's head. |
Sheesh. If an amp is making 100 watts into 4 ohms it is the exact same amount of current whether the amp is tube or transistor. Ohm's law (and the Power formula which derives from it) says so: 100W = Current squared times Resistance.
The speaker is 4 ohms so:
100W=5 squared x 4 ohms. IOW the current is 5 amps at 100 watts.
The idea that its a good thing that the amp power doubles as the load is cut in half is a bit of mythology. What this suggests is that you won't always have flat frequency response in your room with every amplifier (notwithstanding the effects of the room itself).
A further note: in the past I've seen amps that claim that they can make 80 amps or some such. What exactly are they try to say? Giving the benefit of the doubt, let's use a one ohm load for the amp. This gives 1600 watts! 'Current' ratings like this are actually a rating of how much current is available when you short the power supply for 10ms. We do that easily with our tube amps...
The fact of the matter is that in general Magnaplanars sound better with tube amps then they do with transistors. They don't always play as loud, but they do sound better. 'High current' amplifiers (IOW: transistors) are about volume rather then finesse. |
Try the the moscode 600 and forget about the theories. there is one for sale on this cite. |
Thank You for the response, I do understand now what I am looking for and this Current Issue.
Dave |
The way Atma-sphere describe the use of "high current" is incorrect. High Current amplifiers enjoy the ability of being able to return a driver to its resting point better than a low current amplifier.
A quick way to describe this is high current amplifiers are like having stiffer shocks, when the woofer is moved by an input it does not come to rest immediately because its suspension is compliant. A high current amplifier when faced with the electrmechanical energy created by a woofer will present a higher resistence to the moving woofer stopping it sooner. Low current amplifiers cannot "control" the driver with the same authority and that is why many tube amplifiers (low current) have a boomy bass, they can't stop the driver.
The OTL actually does a better job that a transformered tube amp, but 30 amps control the driver like 80 amps.
Magneplanars benefit a great deal in the bass by getting control from a "high current amplifier" because maggies need help stopping or coming to rest. That's why you'll see Bryston 7B's on maggies at shows. Helps control the panels.
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Damping factor is an old myth that has many advocates. That is what D_edwards is talking about above.
The simple fact of the matter is that damping factor has marginal effect on most drivers. Yet, we hear differences- what are they about?? What is happening is that in a 'low damping factor' amplifier (IOW 'low current') as the impedance of the load gets closer to that of the output impedance of the amplifier, the amplifier will make more distortion. It is important to understand that this type of distortion occurs without the amp clipping.
As audiophiles we have developed words for this type of (harmonic) distortion. A moderate amount of distortion is described as 'bloom' or 'warmth', excessive amounts are described as 'muddy' as in 'muddy bass' or as in 'loss of control'.
What is important here is that the driver is not contributing to this, these are artifacts of the amplifier.
Magnaplanars have always sounded their best with tubes. The reason that transistors get used with Maggies is usually power, not control. It is quite expensive to develop power with tubes and Magnaplanars (particularly older ones), require a lot of power to get high volumes as their magnets are located on only one side of the driver.
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"Damping factor is an old myth that has many advocates."
All I have to say to this is, you can't measure a myth.
"The simple fact of the matter is that damping factor has marginal effect on most drivers."
In your opinion. Since your amplifiers have little I would expect little effect compared to the SS monsters. When you're dealing with a hobby that deals with minutiae I would say the effect of "damping factor" is very significant especially on dynamic drivers. That is , it is measurably significant.
"What is important here is that the driver is not contributing to this, these are artifacts of the amplifier."
? The amplifier and the speaker are one circuit, so the speaker makes its contribution also. The Halcro amplifiers
are perfect amplifiers from a technical standpoint put since speakers aren't close to taking advantage of this perfection, they suffer due to the speakers contributions.
In a sense I agree with what you're saying but this Harmonic distortion can be had in solid state amplifiers too.
"Magnaplanars have always sounded their best with tubes."
In your opinion. I think Classe & YBA and Ayre amplifiers make it rough going for tubes especially when you consider the price point one may be seeking an amplifier for the 1.6's.
I would be curious to which speakers you believe don't sound better with tubes. Can we agree that would be a short list of speakers you don't like so you don't care what amplifier is on them? (hope that's not too direct a question or statement)
I heard the $15,000 Warner Imaging amplifiers easily best your $30K amplifiers on Sound Lab U1's, I consider that a defeat on your home court. Admittedly your amplifiers embarrassed the Wolcotts, Lamm's and Pass X600's amplifiers so don't fret. I like your amplifiers, if I had to buy tubes they would be the ones. But I don't see why you have to run around this issue. Tubes have limitations and they have advantages. Same with solid state.
Why don't you say that the propensity for Magneplanars drivers to exhibit an overshoot upon higher musical input means you may want to seek an amplifier that has a slower rise time (output transformed amps), something the Atmospheres do not exhibit or have. You may want a harmonically rich amplifier like a Music Reference RM-200 or a Classe CA-200. This will help the Maggies stay linear and provide you with a smoother sound. My (the atma-sphere) affordable amplifiers are low powered and this will not press the Maggies as hard dynamically and will net the same result of a fuller richer sound do to the higher harmonic content in my designs but you my be lacking in total volume(output) if your room is moderately large or larger, especially with the MG12's, you'll need more power.
Simply trying to make a solid state advantage dissappear by saying the price of high current is poorer sound only makes your amplifiers victim to the same statement. Since your amplifiers probably have some of the highest current output of tube amplifiers on the market. Which is why they are so good, so good infact that I make exception when I talk about tubes for your designs and mainly your designs (Atma-sphere) alone.
"The reason that transistors get used with Maggies is usually power, not control."
In the end I generally agree, most solid state amplifiers emphasize the technical weakness of the Maggies. But not all. And Magneplanar demand a balance of power and harmonics which tubes get left out due to the comment below. Again reiterating Atma's comment about price.
Magneplanar is a cheap speaker for the performance, this is what creates the amplifier conundrum. |
Output impedance is what damping factor is about, IOW it is the ratio between the output impedance and 8 ohms. However measurable, it has hardly any effect on the loudspeaker, unless we are to believe that a speaker displaced is to stay that way when the voltage is removed. Of course that notion is fanciful- the speaker returns to rest. Damping caused by the amp has no effect as the amp *at any time* is producing a voltage that causes the speaker to displace to a specific location with respect to its motor (magnet or ES field). Thus: Damping factor is a popular myth, an urban legend that is made up.
As far as Halcros being perfect?? Sorry, but they are far from it! I can run a demo anytime to dispell *that* and did so at THE Show in Las Vegas, where they were two doors down with the same speakers we were running. The differences were thus very apparent.
It is a rare speaker that does not sound better with tubes, although some will exhibit compromise in some areas (Which are always issues of load impedance). IOW tubes are better sounding in general than transistors in general.
It sounds like you need to hear a set of the MA-2 MkIIIs, which you did not hear when you made your comparison. You must not have played material with bass, else you would have noticed that the Warners weren't making what they should have on the Sound Labs. I suspect you like things brighter than I do, which the Warners would have been. Sound Labs do that with transistors. Its they way they work.
I think you do not understand the 'current issue' but don't this is not an attack- this issue is generally misunderstood :/
Here is what is happening in audio today: There are 2 paradigms that are in conflict. One is the Voltage Paradigm and the other is the Power Paradigm. In the VP, it is assumed that the only thing that is important to measure in amp and speaker specs are voltages. This is the reigning paradigm. OTOH the PP assumes that it is important to measure power response, not just voltage. In this camp, (knowingly or not) are ESLs, magnetic planars, horns, single driver speakers and a variety of box speakers; all which sound better if used with an amp that will make the same power regardless of impedance. SETs and other zero-feedback amps fall into this camp. SO- our amps may have 'current', but only in the context of making Power, without the price of feedback, which increases odd-ordered harmonic content so objectionable to humans.
Magnaplanars can have amazing performance for the price so it is important to winnow that out of them. If you need shear volume, you may have to go solid state, but for nearly everything else, tubes rule. |
Matti Otala....the guy who did all the work on "TIM" wrote a paper for the AES (and believe it or not.......they accepted it! Or course, this was before he got under their very thin skin with his TIM work.)
Anyway....he showed by some complex mathematical mumbo-jumbo that the drive requirements for a speaker can actually be lower than its DC resistance would dictate.
Bottom line is.........in your case.........Maggies do not exhibit this phenomenon, as cone drivers in boxes do.
Low drive impedance may "grab" the panels better, but there is not necessarily a direct correlation between output Z and drive current.
Make any sense to you???? |
