I have been following this thread and feel its time to post, seeing you have now called George a troll for the second time.
George has nothing to gain from these posts, as he does not build amps or speakers, AS YOU DO! He has presented nothing but facts, and left out statements of linked reviews you presented.
And as for my own experience with the Zero Autotransformer, Ive tried them many times, and on a matched amp/speaker combos, they are a big step backward in sound quality IMO. They are as George puts it a band-aid fix, for people who have a mismatched amp/speaker combo that cannot be driven correctly - yet have no desire to change either to correct the mismatch and fix the underlying problem.
Sure, they can live with what they have using the Zero, but that will introduce another set of problems that then affect the sound quality. Is it worth $1140 for a band-aid fix??????? Or should they fix the mismatch problem, THAT is the real question???? |
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You'd be far better off saving the $1140us for the Zero's and putting towards the right amp or speakers, instead of masking the problem with the Zero's, which itself has it's own set of problems.
Cheers George |
Or ... are you saying the relationship between an amp's output impedance and an ESL's varying impedance plot is simply not a relevant consideration to the ESL's sonic output because of some unique or different electrical characteristic peculiar to ESLs?? As I have pointed out before, with all ESLs, the impedance curve is not a function of a driver in a box. In addition, the impedance curve is also not the efficiency curve. IOW, the speaker has the same efficiency at all frequencies. Note that I used the word 'efficiency' as opposed to 'sensitivity'. I am restating my second paragraph above slightly, but if I had used 'sensitivity' what would be happening is that the impedance plot would also be a sensitivity plot. The reason is that the speaker's impedance plot is based on a capacitor. The result is that an amplifier that operates in the Voltage Paradigm will make too much power at high frequencies due to the low impedance, and usually not enough power at low frequencies for exactly the same reason. For this reason you will find that a lot of ML users that have solid state amps likely have them fairly close to the wall, which gets some bass reinforcement. Most ESLs, like any panel speaker, should be 5-6 feet from the wall. I think now you see why the ZERO is so useful when dealing with this speaker. But I will explain: if you use a solid state amplifier one of the really likely results is that while detailed, it will also be noticeably brighter than reality. I've experienced this first hand many times. Now if you use a Power Paradigm amplifier, as Al has pointed out, the 'output impedance' of the amp will interact with the low impedance of the speaker at high frequencies and you will experience a roll-off. This is why many tube amplifiers (in fact most tube amps) sound a little dark on that speaker if not outright rolled off. Those with negative feedback will of course sound less so (but of course negative feedback causes all amplifiers to sound bright due to trace amounts of odd ordered harmonics being introduced). Now if you just want things to sound natural with no roll off and no brightness, what to do?? That is where the ZERO is handy. It raises the impedance of the load enough that a tube amp can begin to operate within its constant power region. In this way you get high frequency speed and extension, while at the same time getting bass extension and impact. A long time ago ML made a speaker called the CLS I. Unlike the newer iterations, it had a more traditional ESL impedance plot (meaning it was higher impedance like the older Quads) and it was a breeze to play it with a tube amplifier. As we all know (or should know) transistor amps don't make a lot of power into higher impedances (+16 and +32 ohms), IOW it may well be that such an amp might only express about 1/4 of its 8 ohm power. It is for this reason that a 100-watt tube amp can keep up with a 400-watt transistor amp on Sound Labs BTW. Anyway, ML realized that if they were to sell speakers to the solid state market, which at the time was about 90% of the amplifier market, they were going to have to do something. The result was that succeeding speakers had much lower impedances, with the 0.5 ohm 20KHz impedance you now see. The ZERO corrects this issue so tubes can be practical on the speaker. |
Someone should sign up to do a "paradigm" shootout, ie the best of voltage versus the best of power paradigms. Of course, finding an unbiased doer or doers for something like this could be the hardest part.
I would volunteer someday, perhaps after I retire eventually, although I doubt I will have the financial resources needed to put into two complete and alternate SOTA systems that could both truly push things to their limits. :-) |
"In otherwords it will do the classic thing that can happen with low current or high output impedance tube amps "behave like a fixed tone control" instead of being flat into all loads."
That's a very interesting analogy!
I suppose, its a question of who is in charge, ie which component is going to dictate the parameters of the overall system that works best.
It makes sense that from the perspective of the amplifier or specifically the designer of a tube amplifier, they want their baby to be the one in charge.
The speaker designer trying to make a compact quality speaker with extended flat bass response that most might be willing to put in their rooms has a different perspective. The price paid in this case is more demand on the amplifier to help deliver the desired results.
Two different paradigms/ways of approaching things as Ralph likes to point out, each with unique strengths, weaknesses, and tradeoffs. Its good to be able to have the choice. |
Its funny how there are always two ways to look at good sound.
1) technical
2) practical/case by case
Nothing guarantees each perspective will resulting the same choices/solution. Why should they each case is different even if for no other reason than room acoustics and how each person hears. Would we expect two people to choose the exact same pair of shoes? No. But we all kinda know what makes some shoes better than others. That's the technical perspective and the only one of global value. But then , the shoe gotta fit.... |
"Hence, based on what Al explained, using a tube amp which has a "high'ish" output impedance will likely result in sonic coloration to some degree."
Yep. The specs give you guidelines but cannot answer what sounds best in each case. The key part is "to some degree". The question is always which colorations and to what degree. The answer will be different likely in each persons case though the specs might indicate certain approaches to yield the best results overall. |
03-31-14: Tomcy6
Of course not every amp can handle the job when you've got a speaker that has an impedance of .5 ohms at 20khz. But you don't need a lot of power to reproduce most musical content at 20khz either. True, but if the amp cannot keep constant voltage at 20khz it will result in the treble being shelved down no matter what volume level you are listening to, resulting in a softened treble, some unexperienced might call this smoother, but their having themselves on. (as the sterophile test reports state) Quote Sterophile: " The shape of the impedance trace will result in the Montis's top octaves shelving down when the speaker is driven by a tube amplifier having a high source impedance. This is why Robert Deutsch found that his Audiopax amplifier sounded too soft and lacking in definition." Cheers George |
Tom, you quote the ML manual as advising that "an ideally stable amplifier will typically be able to deliver nearly twice its rated wattage into 4 Ohms and should again increase into 2 Ohms."
My take-a-way is that ML recommends using a rock-solid stable SS/Voltage Paradigm amp, which as discussed above has a very low output impedance. Stated differently, the ML ESLs in question were likely voiced to be driven by a SS amp.
Hence, based on what Al explained, using a tube amp which has a "high'ish" output impedance will likely result in sonic coloration to some degree. As Al also said, some may not find this to be a problem and that's ok. :)
So ... after all that has been written, I think the best answer to the OP's Q is that if he/she really wants to use a tube amp to drive his/her ML ESLs, consider a low output impedance BEAST that can deliver serious current.
Frankly, I would be biased (pun) in favor of using a high quality/high power SS amp e.g., a Pass, Ayre, Bryston, inter alia.
Regards,
Bruce |
I was just giving you guys a hard time. That doesn't come through in print very well. We get too serious sometimes.
Of course not every amp can handle the job when you've got a speaker that has an impedance of .5 ohms at 20khz. But you don't need a lot of power to reproduce most musical content at 20khz either. The highest fundamental on a guitar is less than 1khz. Overtones are very important but don't need a lot of power to reproduce.
Robert Deutsch had no problem with the 40wpc Prologue Premium Integrated and the ML Montis.
Here is what Martin Logan says in the manual for their current hybrids:
What size amplifier should I use?
We recommend an amplifier with 100 to 200 watts
per channel for most applications. Probably less would
be adequate for our smaller hybrids or when used in
home theater where a subwoofer is employed. Our
hybrid designs will perform well with either a tube or
transistorized amplifier, and will reveal the sonic character of either type. However, it is important that the
amplifier be stable operating into varying impedance
loads: an ideally stable amplifier will typically be able
to deliver nearly twice its rated wattage into 4 Ohms
and should again increase into 2 Ohms.
And:
Could you suggest a list of suitable electronics and
cables that would be ideal for Martin Logan speakers?
The area of electronics and cable choice is probably
the most common type of question that we receive. It
is also the most subjective. We have repeatedly found
that brands that work well in one setup will drive
someone else nuts in another. We use many brands
with great success. Again, we have no favorites; we
use electronics and cables quite interchangeably. We
would suggest listening to a number of brandsand
above all else trust your ears. Dealers are always the
best source for information when purchasing additional
audio equipment.
So, you don't want an SET but you shouldn't be too worried about that .5 impedance either. ML did not say the amp has to double wpc with each halving of impedance, not even close. I do not think that a company that has lasted as long as ML has in the high-end world could get away with advising customers to use amps that make their speakers sound bad.
So, We need to be aware of specs but Trust your ears and Enjoy your music! |
It's only cruel to an amplifier if it's not up to the task. |
Al, perhaps the EPDR article I referred to above might put a little gloss on what you said. The underlying thesis of the EPDR article is that a speaker's "nominal" impedance is further reduced if it is coupled with a negative phase angle at the particular frequency in question. So, if the "effective" impedance, or EPDR, is even lower, I can only assume that the "db delta" between a SS amp and a tube amp, even with a "low'ish" output impedance, would likely be greater. And I believe you surmise the same in your last post.
I think the take-a-way for us is that we may not be able to tell whether a particular amp/speaker combo will be a good match by looking at specs alone. But we should be able to identify (or at least be wary of) a combo that may be a bad match. Of course, if someone likes sonic coloration -- hey, all the power to sonic coloration.
Yeah ... I agree with the comments above, either the manufacturers and/or the dealers need to do a better job of helping customers understand this stuff before pushing product.
Thanks again Al. |
Bruce, thanks. Youre welcome! If ZEROs are used to double the ML's apparent impedance plot, would that change your calculations? It would narrow the gap somewhat. The 11 db figure for the solid state amp wouldn't change, but the 6 db figure for the tube amp having a 2 ohm output impedance would increase to 8 db. So the difference would be reduced from 5 db to 3 db. Also, maximum power capability for the solid state amp would probably be cut in half, with distortion performance being improved as long as the amp is operated within that reduced power range. I'm not sure that it's possible to meaningfully generalize about what would happen in those respects in the case of a tube amp, with this kind of wide variation of speaker impedance as a function of frequency. I believe it would depend on the particular amp, and whether it is OTL, SET, push-pull, high or low feedback, etc. Did the ML's phase angle plots factor into your calculation? If so, directionally, how so (if phase angle is negative or positve)? I intuit that harsh phase angles can constrict the SOA of an amp (SS or tube). I am not clear of the impact on sonic coloration, assuming the amp is operating within its respective SOA. As I indicated, the phase angle was approximately zero at 46 Hz, and I ignored the -20 degree phase angle at 20 kHz in order to simplify the calculation. For purposes of a rough ballpark calculation that seems reasonable. It might not be, though, in the case of other electrostatics where phase angles may be more severely capacitive (i.e., negative). Off the top of my head Im not completely certain what the directionality of the coloration effects would be in those cases, assuming the amp is capable of handling the increased difficulty of the load, and supplying the necessary increase in current. For a given impedance magnitude, such as 2 ohms in this case, I believe that a severely negative phase angle would mean that the resistive component of the impedance (which is the component that can absorb power and convert some of it to sound) would be smaller. I believe that would tend to increase sensitivity to output impedance differences between amplifiers, and therefore exacerbate the difference between the solid state and tube amp calculations I provided. As I say, though, Im not entirely certain of that. You ask some tough questions :-) Best, -- Al |
That's right George. My ARC Ref 150 might (???) be able to handle the current demands because it has a beefed up power supply -- 1040 joules. And, as I mentioned above, the output impedance off the 4 ohm taps is roughly .5 or so ohms. As a result, my amp performs somewhat like a solid state amp.
Hopefully, Al will come back with a response to my follow up questions: (1) whether ZEROs will change his calculations; and (2) how does the phase angle spec at a particular frequency affect his calcs.
That folks is why I persisted with my comments. I can't do the math, but after 2 or 3 years of this back and forth with Al, Ralph and some of our other tech members, I better appreciate the challenge of matching amps and speakers. Also, when I see that a speaker's impedance plot is literally off the chart, e.g., the ML ESLs and some of the B&Ws, I raise an eyebrow.
So ... this goes back to what Ralph (Atmasphere) said all along. Optimally, if a speaker manufacturer could design a speaker with a flat impedance plot, say between 8 and 16 ohms, with a zero phase angle across the frequency spectrum, the SPCA would go out of business.
And once again, the SPCA stands for the Society for the Prevention of Cruelty to Amplifiers. :)
Cheers,
Bruce |
Ralph is here to sell his products. |
03-30-14: Tomcy6
Someone should tell Martin Logan about all this. Those idiots are telling people that their speakers can be used with a wide variety of tube and solid state amps. Some tubes can drive them without becomming too much of a "fixed tone control" (ie: not flat from 20hz to 20khz), but they need low output impedance to do it, below say 1ohm from 20hz-20khz) like ones I metioned earier, which usually have a fare amount of negative feedback on them to keep them below 1ohm output impedance. They also need to back it up with a bit of watts also. Cheers George |
^Yes, someone should do it immediately, as they might be inadvertently garnering more sales.;-) |
Someone should tell Martin Logan about all this. Those idiots are telling people that their speakers can be used with a wide variety of tube and solid state amps. |
Thanks Al .... that's exactly what I surmised the directionality of the impact might be. Btw, if ZEROs are used to double the ML's apparent impedance plot, would that change your calculations?? And your comment about whether any amp, SS or tube, can drive the MLs within its respective SOA (see EPDR article) is a whole "nuther" kettle of fish.
Btw, did the ML's phase angle plots factor into your calculation? If so, directionally, how so (if phase angle is negative or positve)? I intuit that harsh phase angles can constrict the SOA of an amp (SS or tube). I am not clear of the impact on sonic coloration, assuming the amp is operating within its respective SOA.
Incidentally, to my sorry old ears, I find a sonic coloration of even 1.6 db to be noticeable. I base that assertion on my amp/speaker combo.
Based on John Atkison's review of my amp, he reported that the output impedance off the 8 ohm taps is about 1'ish ohms, resulting in output voltage regulation variation of +/- .8 db (ergo a theoretical spread of 1.6 db). By contrast, those figures are roughly halved off the 4 ohm taps.
In practice, I find that my speakers sound less forward and have deeper, more extended bass when driven off the 4 ohm taps. That is consistent with the impedance plot of my S8s, which have roughly a 20 ohm peak at 2K Hz (x-over point) as compared to a 4 ohm saddle in the "power range" of 60 to 500 Hz).
Thanks again Al. You manage to lift the veil of confusion for non-techs folks like me.
Regards,
Bruce |
03-29-14: Bifwynne
Perhaps Ralph or one of the other tech members can speak to how much SPL variation will result if the "wrong" type of amp is used. Perhaps, for discussion purposes, we should assume the MLs were designed to be driven by a SS "constant voltage paradigm" amp and the "wrong" type of amp is a Power Paradigm amp. Hi Bruce, I did some quick calculations for the OP's Aerius, based on John Atkinson's measured impedance curves shown here. It should be kept in mind that the impedance characteristics of the Aerius are significantly less demanding than those of many other Martin-Logan speakers. The extremes are a 25 ohm peak at 46 Hz, with approximately a 0 degree phase angle, and a 2 ohm minimum at 20 kHz, with approximately a -20 degree phase angle. To simplify the calculations I ignored the effects of the -20 degree phase angle. For a given input level to the power amplifier, a solid state amplifier acting as a voltage source will put approximately 11 db more power into the speaker at 20 kHz as it would at 46 Hz, as long as it is operated within the limits of its power capabilities. For a given input level to the power amplifier, a tube amp having an output impedance of 2 ohms will put approximately 6 db more power into the speaker at 20 kHz as it would at 46 Hz, as long as it is operated within the limits of its power capabilities. If we assume per your question that the speaker is designed to provide flat frequency response when driven by a solid state amplifier, the speaker's response when driven by that tube amp would therefore be rolled off by 5 db at 20 kHz, relative to its response at 46 Hz. That difference certainly figures to be audible, although not necessarily objectionable in many circumstances. The difference will of course be significantly greater with amplifiers having 3 or 4 ohm or higher output impedances, and with many other Martin Logan speakers. What seems likely to often be more significant, however, is simply the ability of the amp (regardless of whether it is tube or solid state) to cleanly generate enough power at deep bass frequencies, into the high impedance. Obviously that factor is highly dependent on the dynamic range of the recordings that are listened to, as well as on the listening distance, room size, and volume preferences of the particular listener. Best, -- Al |
03-29-14: Tomcy6
I think that ML designed their current line to be used with either tube or ss amps, the choice being the user's. Yet if you Google images for previous big HiFi shows, and look at specific Martin Logan rooms demo's, as far as I saw nearly evey demo by ML was done with big SS amps like Krell and such. The only ones I saw driven by tubes were not in a Martin Logan rooms, but were in an tube amp manufacturers rooms, who were using ML powered bass hybrids for their speakers. Cheers George |
Bifwynne and everyone else,
Thanks for your efforts to clear up the technical issues involved. |
Quick postscript: my posts are not just academic. The OP is asking about matching a tube amp with ML ESLs. My comments are trying to focus attention on whether the ML ESLs in question should be driven by a low impedance amp that acts as a constant voltage source, i.e., a typical SS amp or a low impedance tube amp.
As I said above, "there are tube amps, ... and then there are tube amps." My somewhat tongue-in-cheek point is that if the ML ESLs were designed to be driven by a low impedance amp, then the OP should be cognizant about the output impedance of the tube amp he has in mind. The consequence of using a "high'ish" output impedance tube amp like an Atmasphere OTL is that the sonic colorations may result in augmented bass and shelved treble. Of course ... even a low impedance tube amp may need some serious current capabilities, even if it performs SS-like. Consider the EPDR article and its reference to SOA.
By the way, as I also mentioned, while ZEROs may raise the apparent across the board impedance load presented to the amp (SS or tube), I am dubious that the device will smooth out the sonic presenation of the MLs if the wrong type of amp is used. Perhaps Ralph or one of the other tech members can speak to how much SPL variation will result if the "wrong" type of amp is used. Perhaps, for discussion purposes, we should assume the MLs were designed to be driven by a SS "constant voltage paradigm" amp and the "wrong" type of amp is a Power Paradigm amp.
I surmise that if the tech members respond, we will all gain a better understanding of whether one should drive MLs with a Power Paradigm tube amp if they were voiced to be driven by a SS/Constant Voltage Paradigm amp. |
Tom, if you read my posts, I framed my question by referring to those tube amps having a "high'ish" output impedance (say 3 or 4, or more ohms).
By contrast, some amps like my ARC Ref 150, have a "low'ish" output impedance, possibly because they use negative feedback. Specifically, the output impedances off my amp's 4 and 8 ohms taps is about .5'ish and .6'ish ohms, respectively. As a consequence, the Ref 150's output voltage regulation is pretty tight: about +/- .4 db and +/- .8 db off the 4 and 8 ohm taps, respectively. So in effect, tube amps that have a low'ish output impedance function somewhat like a low impedance SS amp -- constant voltage source.
I mention all of this because you say in your last post that "ML approves of using tube amps with their speakers." Well ... that may be. But then there are tube amps, ... and then there are tube amps.
Regards,
Bruce |
I think that ML designed their current line to be used with either tube or ss amps, the choice being the user's.
Robert Deutsch spoke with Peter Soderberg of ML who told him that of the systems he has set up using tube amps, about half prefer the 4 ohm terminals and half prefer the 8 ohm terminals. So obviously ML approves of using tube amps with their speakers. And with a max recommended amp power of 500 wpc, they also approve of ss amps.
The measurements in the review show some roll off above 5000khz but we all know that a flat frequency response does not mean a good sounding speaker.
In my opinion, these speakers are not beasts to drive and I think you would agree if you listened to them. |
I used to build many SS Class A amps some water cooled back in the 80's 90's they were along the same lines as the ML ML2's but stereo and not such a "bomb or hydroelectric plant" as you guys put it. But they could almost double as well all the way to 2ohm.
I had a led light on the front that used to flash on transients at I think it was 32v (for my Quad 57 owners) this saved my customers from arcing the panels.
90% of my customers were Quad 57 owners, they had never heard their Quads sound so good.
None went back to tubes or SS that couldn't drive the Quad's with a constant near linear voltage across the audio band. Which means for those, an amp that can "almost" double it's wattage for each halving of load impeadnce from 8ohm down to 1ohm
PS Exactly doubling wattage for each halving of impedance is impossible, the ML2's stretch the truth a little with those specs above, but they come close.
Cheers George |
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An amp that can double down to half an ohm gotta be the bomb! |
^The sensitivity while low, isn't terribly challenging, at least for the earlier model. |
Thanks for the Stereophile URL link Unsound. My tongue-in-cheek quip was dead-on: the MLs should be driven by a hydroelectric plant - actually 2; one for the ESL panels and the other for the woofer. :)
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http://www.stereophile.com/content/martinlogan-aerius-loudspeaker-measurements-1998 |
George, again with respect, all your last post tells me is that the Levinson amp is a Constant Voltage Paradigm amp which doubles watts as ohms halves. Your post also states that the Levinson can deliver power into a near short, .5 ohms.
But that doesn't answer my question. I'll restate it -- did the designers of ML and QUAD ESLs design these speakers with the expectation that they would be driven by a SS - Voltage Paradign or tube Power Paradigm amp?? Put aside the difficulty of the load and the amp's ability to drive the beast.
Just simply what did the designers have in mind -- low output impedance (say less than .1 ohms) SS or "high'ish" output impedance (say 3 or 4 ohms or more) tube?? Once we get this answewr, then we can start to respond to the OP's Q. |
Like a pair of these classic, Class A Mark Levinson ML2's 25w monoblocks. http://www.wtconcept.com/levinsonml2/ 25w into 8ohm 50w into 4ohm 100w into 2ohm 200w into 1ohm 400w into .5ohm There's 20watts and then there's 20watts, "no tone control behaviour with these", dead flat frequency response drive to any speaker from .5ohm to 100ohm loading. Cheers George |
Or you could check the ML website. According to ML the hybrids can be driven by amps outputting between 20, yes 20, and 500 wpc.
Maximum power draw is 200 wpc.
Rather than argue theory, give them a listen, then you'll know what amps they make beautiful music with. You may be surprised. |
Ralph and others, with respect, do you know for a **fact** that MLs or Quads were **designed** to be driven by a Constant Voltage Paradigm (SS) amp or a Power Paradigm (traditional high'ish output impedance tube) amp?
Seems to me that just because they work "ok" with one type amp or another, with or without ZEROs, doesn't answer the threshold of whether the sonic presentation of these ESL speakers will be colored if driven by the one type of amp or another.
Or ... are you saying the relationship between an amp's output impedance and an ESL's varying impedance plot is simply not a relevant consideration to the ESL's sonic output because of some unique or different electrical characteristic peculiar to ESLs??
Thanks |
So my sense is to consider the full impedance curve, not just a static number. Maybe that is where "all other matters" are not equal. That is certainly part of it! There is a reason some speakers are considered 'difficult loads' and that is never a good thing as far as the amp is concerned. The OP was about tube amps that can drive ML ESLs. The issue here is that ML has been really trying hard to make their speakers work better with transistors, which is not easy to do, because ESLs want constant power and transistors are constant voltage (see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php. I'm pretty sure I explained all this earlier- a lot earlier: http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1394129996&openflup&11&4#11But if you have a set of ZEROs, its pretty easy, then its just about whether you have enough power, not whether the amp is comfortable with the load. Seems to me 60 watts will make most MLs play reasonably well. |
Mapman, I just noticed that you have class D amps as powerful as they are don't think they are out of the woods when it comes to driving ESL's Their achilees heel is driving low impedances in high frequencies, they behave in a similar fashion. Just look at the black trace that is the frequency response of the Belcanto Ref1000 driving a simulated speaker load, see how it goes all wonky, it should be flat, and that load is no where near as severe as an ESL load in the HF. http://www.stereophile.com/content/bel-canto-ref1000m-monoblock-power-amplifier-measurementsCheers George |
03-28-14: Mapman
My understanding is low impedance in treble region does not present nearly as much of a challenge as same in bass in that exponentially less power is needed for flat treble response. I think that is the main reason why tube amps can do well with those. It will work into that load, but will be "as JA put it" "shelved down in the treble in this instance". This "could" give you the initial impression of a sweeter treble. In otherwords it will do the classic thing that can happen with low current or high output impedance tube amps "behave like a fixed tone control" instead of being flat into all loads. This is where the Zero can be a bandaid fix, but I always believe it's better to fix the problem, by changing the amp or speakers to something that are compatible with each other, than to mask the problem by introdcing a pseudo fix that has it's own set of problems. Cheers George |
Of course a call to Martin Logan company might answer your question with more degree of accuracy.
enjoy |
Music Reference RM200. Amazing hybrid amp can drive low impedance no problem. |
Well that's kind of an important question Mapman because given the wacko impedance plots of these ESLs, hooking them up to a high'ish impedance tube amp could really color their sonic presentation if indeed these speakers were designed to be driven by an amp whose output impedance is measureable in decimals points.
And while in such cases ZEROs may "trick" a tube amp into thinking it's not driving into a short, the sonic presentation will still be skewed because the ZEROs will not flatten or "normalize" the ESLs impedance plot. |
I don't know what designers intended for certain, but I suspect SS amps all the way. ML is pretty mainstream and tube amps and speakers that work best with them is way more of a niche market.
The best ML demos I have heard was off a Krell integrated amp in one case and a similar Classe amp on another occasion.
I have never seen or heard them with a tube amp. |
The title of this thread is "Tube Amp for Martin Logan Speakers." The lst couple of posts give me considerable pause. Let's go back to square one basics.
Seems to me the first question that comes to mind is what did the ESL designers have in mind? That is did they design these speakers to be driven by a low output impedance amp (e.g., SS) or a high impedance tube amp. Regardless of whether the amp in question can drive these beasts without shutting down, with or without ZEROs, the impedance plots are so wacko that matching the wrong type of amp may likely cause considerable sonic colorations.
So, does anyone definitively **know** the answer to my question? What did the designers intend? |
My understanding is low impedance in treble region does not present nearly as much of a challenge as same in bass in that exponentially less power is needed for flat treble response. I think that is the main reason why tube amps can do well with those. |
That's because the McIntosh 275 has quite a low output impedance for a tube P/P amp at .57ohms from the 8ohm tap.(probably has a fare amount of negative feedback)
But the Montis would still be a hard load for many amps as John Alexander's measurements state
" The shape of the impedance trace will result in the Montis's top octaves shelving down when the speaker is driven by a tube amplifier having a high source impedance. This is why Robert Deutsch found that his Audiopax amplifier sounded too soft and lacking in definition."
Cheers George |
Robert Deutsch reviewed the ML Montis hybrid for Stereophile and concluded that despite the .5 ohm impedance at 20khz, the speakers could be driven nicely by the McIntosh 275 on their 8 ohm taps and even by the PrimaLuna Prologue Premium integrated amp. He didn't like the matchup with his Audiopax model 88s though.
In spite of the impedance curve, I haven't heard of people having problems driving them and I haven't had that problem myself. |
Thanks George. Very interesting plots for the Quads and MLs.
Looking at the Quads, I see the bass impedance spike is literally off the chart. Heck, it's almost an open circuit. I don't know, .... schlepping around a 75 amp to a dealer ... auugh. I ain't gettin' the warm and fuzzies.
The MLs have one of the flatest phase angle plots I have ever seen. Even still, I would be concerned that my amp might be challenged driving the MLs because its impedance is incredibly low in the treble region, almost a short.
So here, if I blundered into a combo involving the MLs and the Ref 150 and my back was up against the wall, ZEROs might help. So ... if impedance was doubled, the bass region impedance wouldn't be outrageously high. But jeez, impedance in the treble region is about 1 ohm. Even if doubled, we're still talking about 2 ohms. That's pretty low.
I suppose the only way to know for sure is to try it out and see what happens. But why would I want to drop a ton of bucks on such an uncertain proposition, even with ZEROs.
I gotta tell ya George, ... unless I read a lot of testimonials on A'gon declaring the Ref 150 and one of these ESLs is a match made in heaven, I would be very skeptical. Even if there were a number of approbations, I'd still call ARC and the ESL manufacturers to get a bead from the tech folks.
It kinda raises a different question -- what ARE folks using to drive this ESL speakers? A hydro-electric plant??
Thanks,
Bruce |
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