Would switching amps make a big difference?
Like a number of other PrimaLuna amps your Prologue Sevens have a particularly high output impedance. Stereophile measured 2.6 ohms for the 2 ohm tap, 4.5 ohms for the 4 ohm tap, and 8.5 ohms for the 8 ohm tap. The impedance of your speakers, which is similar to the impedance of many Martin Logan speakers, is spec’d at 4 ohms nominal, 0.8 ohms at 20 kHz. The result of the interaction between those impedances is undoubtedly a considerable amount of rolloff in the upper treble region, regardless of which tap you are using. (The amount of rolloff would be least on the 2 ohm tap, although using that tap with nominally 4 ohm speakers might compromise the maximum power capability and the distortion performance of the amp). Going to the 11a, btw, would probably be even worse in that respect, as it is spec’d as having an impedance of only 0.6 ohms at 20 kHz. So yes, changing amps is likely to make a big difference, and probably for the better from a subjective standpoint as well as in terms of accuracy. Good luck. Regards, -- Al |
A. If Martin Logan speakers is 4ohms, .8 ohms at 20kHZ - ideal amps would have what output impedance?There is a device meant for this sort of thing called the ZERO (www.zeroimpedance.com). Essentially it allows the amp to operate at a much higher load impedance while driving lower impedance loads. Its an autoformer, which is like a transformer but only one winding. Because it only has to deal with a fairly low impedance translation, it actually has wider bandwidth than any tube amp made, even ours (which are full power from 2Hz to 100KHz or more) as it can go from about 2Hz to over 1MHz! So if you seem to have enough power, you might try a pair of these between your amps and the speakers. |
@cdc2 Excellent suggestion by Ralph (Atmasphere). In the absence of a Zero autoformer, though, I would just say that the amplifier output impedance should be a good deal lower than the numbers I cited for the Prologue Seven, which btw correspond to a damping factor of approximately 1. Beyond that the sonics of the specific amp, and how they would synergize with the sonics of the speaker, would be the predominant consideration. Very often amplifier output impedances are not specified (although if Stereophile has reviewed the amp the measurements section of the review will provide those numbers), but damping factors often are specified. And as you may be aware damping factor is inversely proportional to output impedance, and corresponds at least theoretically to the load impedance for which a tap is designated divided by the output impedance of that tap. So the output impedance of an 8 ohm tap should approximately correspond to 8 ohms divided by the damping factor; the output impedance of a 4 ohm tap should approximately correspond to 4 ohms divided by the damping factor, etc. I suspect that a damping factor of at least around 8 or so would be preferable with your speakers, if a Zero is not used. Manufacturers of tube amps having relatively high damping factors/relatively low output impedances include Music Reference, Audio Research, and McIntosh. I would be careful about preamp-to-amp impedance matching, though. I couldn’t find an output impedance spec for your preamp, but the Music Reference RM-200, which I suspect would be a fine match in other respects, has an input impedance of 30K balanced and 15K unbalanced. That is too low to be optimal with some tube preamps. Contact the preamp manufacturer if in doubt about that. Good luck. Regards, -- Al |
If you like the Martin-Logans with tube amplification, you might not like them with solid state. It might be more accurate, but it will be different than what you have now. If your room can handle them properly, get the Impression 11a loudspeakers first and then sort out the amp situation. The ARC room correction will elevate your system performance. That said, at the level of components you already have, $5k upgrading your source inputs coupled with acoustic room treatments is money better spent than an amp or loudspeaker switch. |
Any thoughts on which tube amps work best with Martin Logan speakers?The problem you are up against is that Martin Logan is trying to make an ESL (which is normally a pretty good combination with tubes) to work with solid state amps. The issue is that ESLs have an impedance curve that typically varies by about 9 or 10:1. Whatever impedance it has in the bass, it will be about 1/9th or 1/10th of that at 20KHz. Since solid state amps tend to double power as impedance is halved, right away you can see that the MLs will be a bit bright if the amp actually got away with that. So they make the speaker really low impedance and that prevents the amp from being as bright because even solid state amps have troubles driving 0.5 ohms. But fortunately there isn’t a lot of energy up there so the amp isn't required to make a whole lot of power at that frequency. But the flip side is no tube amp can drive such a low impedance and so makes no power at all. If you find out that you prefer tubes over solid state (maybe because its not as bright) you have a problem- how to drive such a low impedance? That is what the ZEROs are for. IMO/IME you are better off putting out the match rather than putting out the fire- get a set of ZEROs and then your amp will drive the MLs pretty well. I know it works- we’ve had customers with MLs for nearly 30 years. You’ll get your highs back (and likely the amp will sound better overall) without it being bright. |
I have ML Vantage speakers and am using a Van Alstine tube pre. I have biamped the speakers with a Rogue 90 tube power amp driving the electrostatic panels and an Acurus 250wpc SS amp the bass units. Highs are clear and extended and the bass tight and deep, so much so that I no longer use a sub. Best sound I have heard in a small/medium size room from a relatively modest set up. Front end gear is Cambridge Audio CXN streamer and an Exemplar/Denon tube CD player. |
Al is (as always) correct about the Music Reference RM-200 having an input impedance of 30K balanced. Roger Modjeski did that for a reason, but will change that impedance to anything you want. I assume there will be a price to be paid (sonically), but I don’t know what it is. Give him a call if interested. Or get a tube pre-amp that is happy driving a 30K load. |
atmasphere, Let me elaborate on your statement, "since solid state amps tend to double power as impedance is halved, right away you can see that the MLs will be a bit bright if the amp actually got away with that." Actually, I think that although the SS amp has the capability of providing 2x the power as impedance is halved, the SS amp is still flat in freq response at any given moderate power demand for higher impedance. For example, a 200 watt amp capability at 8 ohms will still output the same power across all freq below 200 watts. I would be wrong if this SS amp only puts out 100 watts at 16 ohms, 50 watts at 32 ohms, etc. What do SS amps usually put out at these much higher impedances? If my numbers are correct, then for an electrostatic whose load varies from 32 ohms in the bass to a fraction of 1 ohm in the HF, the sound below 50 watts of output would be uniform across all freq, not bright. |
@mijostyn Don't include the parentheses at the end of the link. A resistor will simply absorb power. The ZEROs transform the impedance so you get more power and less FR error. @viber6 This statement is incorrect: Actually, I think that although the SS amp has the capability of providing 2x the power as impedance is halved, the SS amp is still flat in freq response at any given moderate power demand for higher impedance.If the amp is behaving as a voltage source, it will double power as impedance is halved. This also means it will cut power in half as impedance is doubled. The solid state amp will only have flat response if the speaker its driving is intended to be 'Voltage driven'. ESLs are a technology that isn't based on the Voltage Paradigm (see http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php for more on that). Under the voltage rules, the impedance curve of the speaker is also effectively a map of its efficiency: peaks in the curve represent resonance, dips represent a loss of efficiency (such as at crossover points). For example if you have a woofer in a box it has a resonance in that box. To control that, the amp has to put out *less* energy (power) into that resonance, which is also seen as a peak in the impedance curve in the bass. ESLs are not based on a driver in a box. Their impedance curve is essentially based on a capacitance. So with a typical ESL where the impedance varies over about a 10:1 range (the Martin Logans are no exception; 4 ohms in the bass and 0.5 ohms at 20KHz) you can see that to make 92 dB at 50Hz a Voltage Paradigm amplifier (voltage source) will make X amount of power; to do the same thing at 10KHz it will have to also make X amount of power, but in reality is will be about 4X the power because its voltage output is constant with respect to impedance and at 10Khz, the MLs are about 1 ohm. The only thing that prevents this from happening is that these HF impedances are so low that the speaker cable itself has a DCR that becomes significant, and a good number of solid state amps can't double power into such low impedances (IOW they are not perfect voltage sources). IMO Martin Logan is trying to make an ESL that works with solid state rather than tubes but to this end (again IMO) they are only partially successful since brightness is part of the result; inevitable when you mix transistors (Voltage Paradigm) with ESLs (Power Paradigm). |
atmasphere, The essence of my post is that although the SS amp has more power capability into low vs high impedances, that doesn't mean the SS amp will have a tonal balance skewed toward the HF when driving an electrostatic speaker. To use our numbers, consider an amp with max capability of 200 watts into 8 ohms, 50 watts into 32 ohms, 800-1600 watts into 1 ohm. Let this amp drive an electrostatic speaker whose impedance is 1 ohm at 20,000 Hz, 8 ohms at 2500 Hz, 32 ohms at 625 Hz. This assumes impedance exactly inversely proportional to freq, although I have ignored capacitive reactance, the true parameter. At 30 watts of output, the amp will put out that same 30 watts into any freq for an even tonal balance. For 200 watts of output, only freq above about 2500 Hz will be undistorted into that speaker, whereas at freq below 2500 Hz the amp cannot put out as much undistorted power, so I agree that under these conditions the amp will sound bright driving the electrostatic speaker. |
At 30 watts of output, the amp will put out that same 30 watts into any freq for an even tonal balance. @viber6 No, that isn't correct, assuming the amp acts as a voltage source (as almost all solid state amps do, and as some tube amps do to a relatively loose approximation). In the case of an amp having voltage source characteristics, i.e., very low output impedance, for a given input voltage to the amp it will provide an output **voltage** to the speaker that is essentially the same regardless of frequency, assuming the amp is operated within the limits of its voltage, current, power, and thermal capabilities. And that same voltage will result in more current and consequently more power being delivered into low impedances than into high impedances. As you are probably aware power delivered into a resistive load equals voltage squared divided by resistance. It's somewhat more complicated than that when capacitive or inductive reactance is involved, but I'm putting that complication aside to try to clarify Ralph's point, which relates to delivery of power (as opposed to voltage) into the speaker. And which relates to frequency response flatness at the output of the speaker, not to frequency response flatness at the output of the amplifier. Frequency response flatness at the output of the amplifier, on the other hand, is normally defined in terms of how the relation between amplifier output voltage (not power) and amplifier input voltage varies as a function of frequency. That characteristic will indeed be essentially flat in the case of a good quality voltage source amp, as long as the amp is operated within its capabilities. But that is not relevant to the point Ralph was making. Regards, -- Al |
Most speakers are designed to approach a flat voltage response, not power, and amps to be a voltage source. If the source impedance of the amp is rather high (tubes) then there will be an HF roll off. The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off. A speaker designer who designed a speaker with a highly variable impedance AND tuned it for a flat power response would be an idiot. |
Most speakers are designed to approach a flat voltage response, not power, and amps to be a voltage source.Agreed, but of course "most" doesn't mean "all." It just means a majority. If the source impedance of the amp is rather high (tubes) then there will be an HF roll off. The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off.The implication of this statement seems to be that in the case of electrostatic speakers, which are what the thread is addressing, that the tonal balance which results when a solid state amplifier is used is necessarily more correct than the tonal balance that would result with a tube amplifier. If that is what you are saying I and I believe many others would disagree. It's worth noting, for example, that the Quad ESL-57, which is revered to this day by many audiophiles, was designed before solid state amplification existed. Regards, -- Al |
cdc2 OP A strong solid state amp is always a good idea to try with ESLs This is good advise, get the right amp that can handle Martin Logan Ethos sub 1ohm loads and -phase angles with current and stability. Stay away from expensive "band aid" fixes like autoformers, save your money and get the right amp for the job instead, your Logans will reward you if you do. The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off.I’ve owned many ELS’s this is so true with all Martin Logans, with the right solid state amps that’s stable and that can drive into that sub 1ohm load, you will get the highs that are "there" at the correct intensity and extended, not muted and rolled off. Cheers George |
((( I’ve been using a Belles 21a tube pre))) Why not check out the new Belles Virtuoso power amp? It has dual mono transformers sophisticated power supply, friendly 100 k input impedance, gain matches your existing Belles preamp, performs beyond expectation and its not digital. Please excuse my phone camera action Best JohnnyR Belles Dealer https://www.youtube.com/watch?v=BSyZuSyO76M |
The performance of a solid state amp might sound subjectively brighter but that’s not because it’s tilting up the highs, but because it’s not rolling them off. A speaker designer who designed a speaker with a highly variable impedance AND tuned it for a flat power response would be an idiot.@rwortman: On an ESL sold state is going to sound bright on two accounts- first it is indeed tilting up the highs because of simple physics: as a voltage source it will attempt to double power as impedance is halved, and since ESLs have decreasing impedance as frequency goes up, there are your tilted highs. This simple fact is inescapable. Google the impedance curve of any ESL and you will see what I mean. The second reason is low level higher ordered harmonic distortion, which causes solid state amps to be bright to begin with and this is why tubes are still around 60 years after being declared ’obsolete’. I would be hesitant to call speaker designers who designed a speaker with a highly variable impedance AND tuned it for a flat power response would be an idiot.an idiot. Some of them are quite brilliant, and like the way tubes sound. You might also consider that before about 1956 or so, all speakers were driven by flat power response as that was the only game in town. |
I have a pair of ML Montis. The impedance curve is quite complex, going from c.3k real at DC, to capacitive, to inductive at the crossover (c. 340Hz) to capacitive, to entirely real at c. 20kHz (0.9ohms) to inductive. Over most of the audio frequency range the impedance "waves" around 4 ohms. I use several amplifiers to drive these speakers, including a pair of Rogue M180s, a Hypex Ncore400 and a Benchmark AHB2. All three amps are stable into the load- all reproduce decent 1kHz square wave outputs.The Rogues, used in the 4 ohm tap mode, have an output impedance looks that like about 0.3 ohms in series with an inductor, and there is a measurable and simulatable loss at 20kHz, but it only amounts to about 3dB, although very low impedance speaker interconnects are advisable. With the Benchmark the HF loss is substantially less, but surprisingly little difference can be heard between the two due to the altered frequency response. The Ncore amp sounds rolled off in comparison to the other two, but doesn't measure significantly differently, which is surprising. Neither the Benchmark nor the Ncore produce any audible high order harmonics in the audio band. The Rogues, on the other hand DO produce audible low order harmonics. The Rogues can be played subjectively louder than the Benchmark despite their having nearly identical power ratings into 4 ohms (180W vs 190W) with the Rogues producing several orders of magnitude higher distortion at the rated outputs. Overall I have settled on the Benchmark as my amp of choice with the MLs. |
I have the ML 13a's and was using a Prima Luna pre with Macintosh amp. It was nice but I always felt something was missing. Went to a Don Sachs all in pre and a pair of Odyssey SS all in monos. I told both builders what I was using and they tweaked the builds to my speakers. I am presently listening to the finest system I've had.....and I've had plenty. |
It worked for me.. This year I swapped out a pair of Vincent Monoblocks for a pair of new PS Audio M700 Digital Monoblocks.. Listed in the best Amps in Stereophile this past year.. Big improvement and now a lot of raw power at 4 ohms, 700 Watts a side.. Better in every way detail, bass and soundstage.. |
Martin Logan ESL's all dive down to around 1ohm with -phase shift as well in the HF. As wynpalmer above found of the three he listened too, the amp best suited was the one that delivers without sounding rolled off or distant in the hf better into that load, the Benchmark, which can give considerably higher current's with lower distortion into those low impedance's. Cheers George |
I’ve lived with ML’s nearly all my life throw in big Acoustat’s before them , they all need an amp that can drive down to 1ohm without sneezing at all, to get the best out of them. And as wynpalmer4 found out even one of the best Class-D’s at the moment the Hypex NC400’s still was not the answer, and ’probably" neither any of the GaN Class-D’s, sure they’ll make sounds out of them and sound "ok" to those that have never heard them at their best, but is that what you want, "just ok?" Cheers George |
I would consider a class-A solid state amp and use u quality tube pre-amp. I am running a pair of vintage ML Quest-z speakers driven by a Plinius SA-100 mkIII amp and couldn't be happier. Pre-amp is by Audio Research. if the Plinius can be found on the used market, I am sure you will be pleased. It will certainly drive ESL-11, ESL-13. Happy listening!!! |
| Post removed |
I think you would achieve much more bang for the buck by changing out your preamplifier. Give the deHavilland UltraVerve a shot, at the very least you will have a preamplifier you can keep for life. I have spent time with your current preamp and with the UltraVerve so not speaking out of school. Below is my room at the show. “Though I've heard the Wilson-Benesch Curve floorstanders many times before, I found that they sounded spectacularly good as driven by Kara Chaffee's amazing deHavilland tube electronics . Nothing I heard at RMAF, save perhaps for the far more expensive Vandersteen/ARC system, could touch this rig for sheer midrange purity, detail, three-dimensionality ." Chris Martens TAS on the 2009 show. |
Wow, I've gotten a ton of useful ideas here to my question and am thinking of starting with the Zero-Autotransformers which should solve the Martin-Logan / amp speaker compatibility issue. Next question is, if I were to replace my admittedly old Belles 21a preamp - thoughts on the following 4 preamps? > deHavilland UltraVerve > Backert Labs Rumba > Don Sachs > Linear Tube Audio |
Of the list above I would do the Sachs or deHavilland. The Backert Labs is an excellent preamp; IIRC it employs an output transformer. Since your amp is single-ended input I don't see an advantage with that. I also have a preference for 6SN7s as a line stage tube- to me they are more robust and musical than 6922s/6DJ8s or any of the 12A*7 series (we use the 6SN7 in the line section of all our preamps); that is how I arrived at this opinion. |
Thanks for all the advice. I decided to try two things. First i ordered a pair of the Zero Autoformers. Just put them in a few days ago and the results were HUGE with my tube amps. My Martin Logan Ethos speakers, sound fantastic. More detail, so much more live and tight from top to bottom. Next I ordered a deHavilland preamp. Which I’ll be testing next. |
First i ordered a pair of the Zero Autoformers.The trick with getting the highs right is something called gain bandwidth product. With most amps this is pretty poor. This can result in a harsh high end and is why a lot of solid state amps have troubles in this regard, especially when confronted with a low impedance load at the same time. The ZEROs at least help out with the latter. Making the amp's job easier is usually audible :) |
A lot of suggestions about how it would sound "on paper" but in the real world the Raven Osprey is a high end bargain. You should consult with Dave the owner- he has integrity and will not sell you on something that won't work. People said the LS50s wouldn't work with a 20 watt tube amp too but the moment i heard the Osprey bring the KEFs to a glowing, euphonic unbelievably refined sweet sound I had to own each. Sound stage to the sky, delicate transparency, as sweet a midrange you could want and plenty of dynamics and slam for a good sized room (16 X 20) In short, Yes. |
I’ve had the deHavilland Ultraverve preamp in for a couple of days now, and it’s taken the system to the next level. While the Zeros helped dramatically by improving the highs, and tightening sound all around, the deHavilland preamp - does an amazing job of making the sound feel live, in the room and for lack of a better word, more tangible. Another great suggestion. Thanks |
