03-26-14: Atmasphere
This can be so significant that the use of an autoformer to raise the load impedance to an otherwise very capable solid state amplifier can result in improved sound. Were this not the case, the insertion of the autoformer would have adverse effects.
OMG, it does, if the listener had ears. I've tried them on a very capable ss amp, and the sound took a bad turn for the worse. Quotes: from the Dick Olsher review that was convienently left out of the excerpts of the reveiw of the link you provided on the Zero website, read between the lines, we all know that reviewers don't like to rock the boat too much. "It is not a panacea, and as you can see from my experience, it does not always pan out. However, if you're the proud owner of an OTL or a low-power tube amplifier and presently driving a 4-ohm loudspeaker load, you owe it to yourself to give the ZERO a try." Cheers George |
Atmasphere, on the surface, I don't think anyone would argue that reducing distortion would be a good thing. But we have seen when distortion reduction specifically and unto itself with disregard for the whole can cause more harm than good.
From the above; it seems that Steve McCormack's thinks that the autoformers made his amp "happier". Well, I might believe that, but that unto itself doesn't mean a whole lot when considering the whole lot.
There is apparently more to low impedance than just "sound pressure" (I'm not putting words in your mouth, am I?). For many years in the past, and very much in the present, and I'll hazard a guess, that for many years into the foreseeable future there will be speakers with low impedances with high end aspirations. I would caution those considering acquiring loudspeakers not to dismiss loudspeakers that have low impedances. There are many, many superior loudspeakers that might be missed out on. There are many amplifiers capable of driving them just as they come from the factory.
With all due respect, we've going back and forth on this subject for years now. Unless there is a drastic change in the audio landscape; as long as you keep making the assertions:
"Now its a simple fact, that there is no good argument for lower impedance (4 ohms or less) loudspeakers in high end audio; that is to say if sound **quality** is your goal."
I will probably object. In an effort to save time and bandwidth, perhaps we can come to some sort of gentleman's agreement on how to deal with this in the future?
BTW, as I read it; George didn't call you stupid, he called one of your suggestions stupid, and that was after you called him a "troll", which was after he posted a link where he recommend your product. This line of posting is somewhat out of character for you. You're better than that. But, hey, we're all human.
Best Regards,
Unsound. |
"You can see in the specs of any amplifier (solid
state, class D or tube) that the distortion is indeed higher
driving a lower impedance load. "
That is true, but still all relative, and 4 ohms does not
mean many amps stop performing well.
Needless to say, the amp has to be up to the task. Most
good quality SS amps these days are quite capable of
performing well into 4 ohms these days it seems. Lower
than that becomes more of an issue perhaps, but better to
listen and determine for ones self the whole story rather
than focus on any one technical scenario. 4 ohm loads are
quite common these days and for good design reasons, not by
error or ommission. There are many valid ways to achieve
excellent results.
Tube amps are a different beast that work best in different
scenarios and subject to their own unique distortion
characteristics, so comparing SS and tube amp distortions is
not apples/apples and of limite.d value IMHO |
Folks, some may find the Stereophile article about "EPDR" quite interesting at this link:
http://www.stereophile.com/reference/707heavy/index.html
I think one important take-a-way is that speaker impedance ratings, by themselves, do not take into account the full picture of speaker's load difficulty. Other factors include a speaker's phase angle characteristics. Take a look at the Final 600i ESL. Talk about an amp ball-breaker.
But perhaps even more relevant to this thread and Ralph's comments is that most amps have a real world "SOA" re power dissipation that is a lot less than one might expect. As defined in the article, the acronym SOA stands for Safe Operating Area. Please note that an amp's SOA power dissipation contracts considerably as impedance decreases and negative phase angles increase in magnitude.
I'll let our techy members comment further, but suffice to say that low impedance loads can cause an amp to operate at or outside its SOA, thereby causing distortion. I surmise that if a particular brand amp's SOA is small when driving a low impedance load, the answer is to buy a more powerful amp that has a less restrictive SOA or try ZEROs.
Final two points. First, the article speaks about SS amps. Nonetheless, I surmise that similar principles apply to tube amps. I understand the SS amps hard clip while tube amps generally soft clip. But I think common to both types of amp is that distortion dramtically increases once the amp exceeds its SOA. The second point is that when Ralph uses the term "happy amp" he no doubt is referring to an amp that is operating within its SOA.
My heads hurts because I have no idea what I just wrote.
Goodnight. |
Clipping is always the devil to avoid when chosing an amp for speakers. Effects of clipping start as subtle and increase to major. Whatever the speakers, be sure to chose an amp that is well beyond being up to the task. Most speaker vendors quote minimum or recommended amp power rating that are suitable to get decent results for most, but not suited to get the best results possible, which is what audiophiles seek. Result is many underpowered systems out there over the years and that is valid fuel for the argument towards speakers that present an easy load.
High efficiency/easy load speakers are a viable solution to the problem, but no the only one, especially these days. Amp technology has progressed and offers major improvement in efficiency these days as well. Monster heavy and big power amps ala traditional Krell, etc. are no longer the only robust option. Class D amps are lightweight, small, efficient and offer more power for the $ than ever.
SO do not disregard modern innovations in amplifier technology when assessing options. THere are more good and affordable ones out there than ever, especially when TCO is considered.
Also, use of powered subs to offload the heavy work in the bass is another very practical tool to choose. WHen powered subs are used (most use Class D amps to very good effect here) a lot of the issues with matching speakers to amps that exist otherwise tend to go away in that the main amp is asked to do much less to drive the speakers optimally than otherwise.
Also when playing vinyl, always make sure rumble and subsonic noise in herent in many phono setups is managed properly and under control. Otherwise, most of the amps headroom will be used to produce noise. High efficiency/easy load speakers might be a band aid in this case, but not the solution. |
Well stated Mapman! :)
I think the EPDR link I provided supports Ralph's comments that low impedance speakers may have an even lower EPDR rating than what is nominally reported or measured. Even more important is that speakers presenting low EPDR factors significantly contract an amp's so-called SOA.
I am not saying that 4 ohm speakers are not good performers. Just that a nominal 4 ohm load in the bass region may really squeeze the amp and possibly result in a referral to the SPCA. At a minimum, a less than optimal amp/speaker match may, as the article explains, result in distortion. So, I happen to think Ralph's comments make sense for the reasons set forth in the attached article.
Bruce
P.S. The SPCA is the Society for the Prevention of Cruelty to Amplifers. |
BTW, as I read it; George didn't call you stupid, he called one of your suggestions stupid, and that was after you called him a "troll", which was after he posted a link where he recommend your product. This line of posting is somewhat out of character for you. Hi Unsound, yes it is, and one should consider that I do refrain from that sort of thing as much as I can. Recommending the ZERO is something I have done a lot, and not just for our amps and I will continue to do so despite George's remonstrations. This is for no other reason than the ZERO really does work. One other thing- to clarify, I am not stating that 4 ohm speakers are bad speakers. I am stating that any amplifier driving them will sound harsher and less detailed as opposed to the same amplifier driving the same speaker that was 8 ohms, were all other matters to be equal. Put another way, a simple method of making a speaker seem more transparent and easier to listen to is to make it be higher impedance. This might be all about how important it is to an audiophile to have increased transparency/detail, coupled with a smoother presentation. I like those things myself. Something I have not mentioned yet is the effect of the speaker cable on 4 ohm speakers- but it should be obvious that they are far more critical for a 4 ohm speaker than the cables are for 8 or 16 ohms. Damping factor of amplifiers is normally stated with respect to an 8 ohm load; that number is initially cut in half with a 4 ohm speaker. Add to that the seemingly low DC resistance of the speaker cable and the damping factor of the amplifier is reduced considerably more that one might intuit. RCA published a nomograph that showed this relationship several decades ago. |
YEs, but realize that tube amps in general will distort even more than SS amps into 4 ohms, so if 4 ohms is part of teh puzzle, the answer is clear.
Any good amp, SS or otherwise can drive an easy load easier.
SO you have to look at all the pieces of each puzzle together in the right way , not take one piece from one puzzle and try to insert it into the the other and then blame it for not working.
Likewise, there is always good, better and best in any case/scenario. Its important to understand impedance and phase related issues in order to assemble the right pieces. Then you can assess system/puzzle A versus B however one likes, but better to look at the overall results than the relative deficiencies or strengths of any one element of design. |
03-27-14: Atmasphere: do so despite George's remonstrations Are you kidding, far from pleading with you Ralph. I agree that an Autoformer is a great (pseudo) bandaid fix for whatever amp that cannot drive a speaker that is not a good match, because of it's inability to deliver current/wattage or is working out of it's SOA (safe operating area) A FAR BETTER FIX IS TO CHANGE THE AMP/S OR SPEAKERS! You state that even a good solid state amp will measure less distortion on it's output from using a Zero Autoformer into a 4ohm load compared to 8ohm. Yes I agree that with the Autoformer even a good solid state amp will measure slightly less distortion at it's output terminals at 4ohms (this is not to say it's out of it's SOA) But it's what happens after the Autoformer (things like phase shifts, damping factor etc) that is far more detrimental to the sound than the slight increase in distortion before it without the Autoformer. EG: What one would basically do to a good amp say like a Pass Labs, Krell, Gryphone or similar amp by sticking an Autoformer on it, is to turn it into the solid state series MacIntosh's that also use a type of Autoformer on their outputs, but without the benifits of using them within the amps feedback loop, to keep the (damping factor, phase shifts, etc) in check. Cheers George |
There are many, many speaker cables to choose from. I'm confident that one would find many (if not most) will work just fine with a 4 Ohm load speaker. |
This is for Ralph, since I'm quoting him. But any others are welcome to jump on it as well.
"I am not stating that 4 ohm speakers are bad speakers. I am stating that any amplifier driving them will sound harsher and less detailed as opposed to the same amplifier driving the same speaker that was 8 ohms, were all other matters to be equal."
I admit my knowledge of electronics is very limited, but this raises a question for me. Is the singular impedance rating of any speaker worthwhile or even all that important? Or is a better question what is the impedance plot across a speaker's response range?
I ask this because for many years I owned Duntech speakers which were rated at 4 ohms. However, reviewing Duntech's impedance plot, it dipped close to 2.5 ohms at two points, the most troublesome being between 60 and 80 Hz as I recall. Considering the power called for at that frequency range and the dip below 3 ohms, well, not ever amp rated to drive a 4 ohm load got off easy!
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. |
I do not manufacture amps that may or may not need the Zero in circuit, so there are no ulterior motives for me to hide or protect. I just don't like to see blanket statements like the Zero will improve all amplifiers regardless of topology. They have their place in that they make an amp that has trouble to drive certain loads with relative ease, able to do so. But it is not the definitive answer, it is a bandaid fix, changing the amp/s or speakers is the way to go in these cases. Here is another point made from Dick Osher's review of the Zero Autoformer that was conveniently left out of the link to the excerpt of the review. "T-Rex 300B SET, a DIY design project in the works (still unpublished) using Plitron output transformers with only 8-ohm taps, and the Lowther DX4 BassZilla - a 97dB.
At his point, it became clear that although bass lines still benefited from the ZERO, overall the T-Rex - BassZilla interface sounded better with the ZERO out of the way."
"Small, but noticeable errors of commission crept in. Soundstage transparency diminished, which reduced the music's intimacy. Microdynamics now sounded slightly over damped, releasing some of the music's tension. The midrange, which for me paints a window onto the music's soul, became slightly cloudier. On balance, I would rather give up 20% of bass definition for a 10% increase in midrange clarity.": As you can read the 300B set amp (and others eg OTL's) not known for good drive current, was improved in the bass area with the Zero, but the midrange diminished by 10% The same 10% detriment will happen to the midrange using a Zero with a good solid state amp or powerful tube amp that have no problem in delivering good bass without the Zero. The word Dick Olsher used "cloudy" in reference to the midrange is also what I heard in my system with the Zero's attached to a good SS amp that could drive the speakers with no problems, and as well as the bass tightness and drive diminished just as much with it in. Cheers George |
George, not having ever used the ZEROS, I can't speak to their pros or cons. Having said that, as I mentioned in one of my posts above, I tried a couple of gizmo tweaks in the signal path in various places and was disappointed. So, I suppose based on those experiences, I would be biased (pun) against inserting **any** artifact in the signal path .... unless my back was up against the wall.
For that reason, I would shy away from using ESL speakers with wacko impedance and phase angle curves, even if ZEROS would enable my amp to drive them. At one point, I was wondering whether picking up a pair of QUAD 2805s would be worthwhile. After doing some reading about their impedance curve, I decided against it.
Hey ... there's a lot of amp ball-busting speakers out there. The impedance and phase angle specs of some "fav" dynamic speakers are killers. So I happen to concur with the parts of your last post that counsels caution when matching amps and speakers.
As I also said above, it is only through dumb luck that my ARC Ref 150 seems (??) able to do a good job with my Paradigm S8s. Talk about amp ball-busters. I think the reason the combo works is because (i) I use a self powered sub woofer to pick up some of the low end load, (ii) the S8s are spec'ed at 92 db sensitivity, (iii) the Ref 150 is rated at 150 wpc, and (iv) the Ref 150 can presumably deliver serious current because it has a beefed up capacitive power supply of 1040 joules.
Btw, I currently use my amp's 4 ohm output taps. Output impedance is probably on the order of .5 ohms or so. If correct, the "actual" damping factor is probably 8 or 10'ish in the S8's bass region (60 Hz to 500+ Hz) because the S8's spec'ed impedance is about 4 or 5 ohms in that frequency corridor. That is clearly better than if my amp had an output impedance of 4 ohms, in which case the DF would be about ONE (1) .... not so good.
Finally, I think there is more we agree about than not. Hopefully, we'll all read each other's comments more carefully to avoid talking past each other.
Cheers,
Bruce |
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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 |
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. |
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 |
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. |
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? |
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. |
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. |
Music Reference RM200. Amazing hybrid amp can drive low impedance no problem. |
Of course a call to Martin Logan company might answer your question with more degree of accuracy.
enjoy |
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 |
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 |
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. |
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 |
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. |
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 |
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. |
http://www.stereophile.com/content/martinlogan-aerius-loudspeaker-measurements-1998 |
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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^The sensitivity while low, isn't terribly challenging, at least for the earlier model. |
An amp that can double down to half an ohm gotta be the bomb! |
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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 |
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. |
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 |
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. |
Bifwynne and everyone else,
Thanks for your efforts to clear up the technical issues involved. |
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 |
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 |
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 |
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. |
^Yes, someone should do it immediately, as they might be inadvertently garnering more sales.;-) |
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 |
Ralph is here to sell his products. |
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 |
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 |
