Tube Amp for Martin Logan Speakers
So, to recap, what did we learn: - output impedance of a 'box' is *defined* as the change in output voltage divided by the current change that caused the voltage variation; - nfb makes the output voltage change smaller for the same current change, so *by definition* lowers the output impedance. We also saw that nfb does not change the 'internal' output impedance of an amp - nfb operates strictly outside the amp proper. Also, we saw that (to a first order) this change in output impedance due to nfb does not change the amps output capability. Lowering the output impedance towards zero does not all of a sudden produce an amp that can deliver gobs of power in very small loads. The as-designed amp capability does not change. A corollary we did not discuss but should be quite obvious: since damping factor is *defined* as load impedance divided by output impedance, output impedance drop due to nfb consequently increases damping factor in the same measure. This was a good exchange! |
Unsound and Bruce, as you may have noted TJN's article that Unsound referenced addresses how impedance interactions affect frequency response at the speaker's INPUT terminals. In itself that says nothing about what the speaker's acoustic output will be like in response to those inputs. I have no knowledge as to whether optimal frequency response of the acoustic output of the Martin-Logan Aerius would result from a flat frequency response at its input, or from a frequency response at its input that is non-flat in some manner. But see the comments in my previous post regarding the Quad ESL-57, and take a look at its impedance curve that I referenced. Best regards, -- Al |
^^ Ah- good. And we now also see why the Power Paradigm is still around some 60 years after it was supposed to be supplanted by the Voltage Paradigm: and that is because amplifiers operating under the Power Paradigm tend to make less odd ordered harmonic distortion. This is partially because nfb will add trace amounts of odd ordered harmonics, even when used in large amounts. The human ear/brain system is very sensitive to these distortions, more so than anything else, as it uses higher ordered harmonics to determine how loud a sound is. As a result, nfb will make an amplifier sound brighter than it really should be (regardless of tube or transistor) because the ear/brain system translates distortion as tonality. This is why two amps on the bench might have the same bandwidth but one can sound bright and the other doesn't. |
Atmasphere, I read your last post again - are you trying to say that even when nfb decreases the voltage drop due to increased current output (the Zout), that doesn't mean that the amp can all of a sudden deliver more power? If so, I fully agree. The amp has it's intrinsic limits in output current and output voltage and nfb cannot change that. Even with nfb, when the output voltage goes up, it eventually gets up to the supply voltage and cannot go higher of course. Same with the output current - the current capability of the amp cannot increase due to nfb. What nfb will do is to keep 'trying' (if you will excuse this antropomorphism) to keep up the output voltage right up to the supply voltage. This is, of course, the reason why an nfb amp generally clips much sharper than a non-nfb amp. |
Atmasphere, your conclusion that someone (certainly not me!) would think if you lower the Zout to zero in a preamp, it can effortlessly drive 4 ohms, is rather far-fetched. As I'm sure you know, Zout has NOTHING to do with what you can or cannot drive, and I would expect that most people here would be well aware of that. A D-type battery cell has a Zout of less than an ohm but nobody would expect it to be able to start their car. :-) . I really have no idea what gave you that particular idea. BTW I gave the example of ss amps' Zout being caused by for instance the transistor gain droop with increased load current. In a tube amp, there are causes for 'Zout' like the internal output tube(s) resistance and transformer losses that cause a drop in output voltage if you increase load current (for instance by connecting a lower impedance speaker). My point was that this Zout in the amp is largely 'virtual' in the sense that you cannot point to a resistor in the amp that would be the Zout. Now what nfb does is making the drop in output voltage with more load less so, thus causing the Zout to appear lower. Actually it is quite easy to measure Zout on your amp. Just connect an 8 ohms resistor as load and set Vout to say 8 volts. The Iload is therefore 0.5 amps. Now connect a 4 ohms resistor and let's say the Vout drops to 7 volts. The Iload is now of course 7 V/4 ohms = 1.75 amps. So we now know that Vout drops 1 V if the current increases 0.75 amps. Therefore Zout is 1 V / 0.75 amps = 1.3334 ohms. Easy, no? |
Jandidden, keep in mind this thread is not about transistor amps. But more importantly you have to be careful here not not violate something called Kirchoff's Law. Actually you will find that such is impossible as it is a law of physics, and not part of legal code :) This law is known also as the law of energy conservation and simply states that the amount of energy in an electrical network is equal to the amount of energy going into that network. What feedback does not affect output impedance: Now if we take two output circuits, one with a high impedance, for example the single ended output of a tube preamp, and that of a transistor power amplifier we will see that due to the lower output impedance of the amplifier that it will drive a lower impedance. Now if what you and George say is true, that adding negative feedback lowers output impedance, it then follows that if we add feedback to the preamp circuit its output impedance will become so low that at some point we can drive a 4 ohm load effortlessly. But what we find is that is not the case. Now you may argue that the preamp output is not relevant, so let's take the case of an SET with a 10 ohm output impedance on the 8 ohm tap. If what you say is correct, its output power will increase if feedback is added when asked to drive a 4 ohm load off of that tap. But again, what we find is that the 4 ohm output power is unchanged. The reason for this is if negative feedback really did decrease the output impedance, the resulting circuit would have the increased current to drive a lower impedance. That of course would violate Kirchoff's Law. Of course, the real way to provide for greater current ability is more output devices, larger heatsinks, output transformers, power transformers and the like. IOW, what is happening is that the term 'output impedance' as used with the Voltage Paradigm is a charged term that actually refers to servo gain in the output circuit and not the actual impedance of the devices involved (all types of which have an impedance greater than zero ohms). One might state that the issue here is semantic- I point it out simply because its use in the context of teh Voltage Paradigm leads to a lot of confusion- but that is how the audio industry is set up. If you are having trouble following this, it is because you are operating within the Voltage Paradigm. The word 'paradigm' has to do with a platform of thought; quite often viewpoints outside of that platform are hard to think about or might be considered blasphemous. A further note- people have accused me of making up the two Paradigms (voltage and power) that I mention in the article at this link: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php In case I run into that I refer them to this google search on the Fisher A-80 amplifier https://www.google.com/search?client=ubuntu&channel=fs&q=fisher+a-80+amplifier&ie=utf-8&oe=utf-8 The very first hit you get at this link is a YouTube image of the damping control of the Fisher amplifier. It is marked 'Constant Voltage' at fully counter clockwise, 'Constant Power' at noon and 'Constant Current' at fully clockwise. This is because there was a time when not all loudspeakers conformed to the voltage model, despite George's and Bruce Rosenblit's remonstrations. Such speakers are still made today, and in increasing numbers. Any speaker than can be driven successfully by an SET will be an example. ESLs are also an example as it will be found that their impedance curve is not based on the resonant impedance of a driver in a box. If you could show that the impedance curve of the speaker (which in most ESLs varies by about 10:1) is also an efficiency vs frequency curve then you would have an argument that the speaker is a Voltage Paradigm device. IOW the ML ESLs are a low impedance Power Paradigm loudspeaker. |
George don't make me blush :-). Anyway. Atmaspere's statement that the INTERNAL Zout doesn't change has another side to it. It suggests that you can open up an amp and point to a component and say see, there's the output impedance. This is not the case. Apart from a few minor things like the resistance of the cabling from PC board to speaker connector, the Zout is sort of virtual. One cause for instance is the fact that the gain of the output transistors drops when you request more output current, so the output voltage drops a bit and that is seen as 'Zout'. As Bitwynne noted, what nfb does is counteract the drop in output voltage so it appears that Zout is now less. But the 'internal Zout' and the Zout with nfb are equally virtual. |
I would like to thank Jan Didden for laying this furfie "NF feedback DOES NOT effect Z=out or damping factor" out in the open, in his usual calm and palpable way. His is a bottomless pit of correct information over at the much more techincal forums, along with the usual others like Nelson Pass, John Curl, and many others, there should be more of them to police bad info on forums. http://www.wordsense.eu/furfie/ Cheers George |
Bifwynne, if I may, not trying to split any hairs, but the term SOA has a very specific meaning for ss devices. The Safe Operating Area defines the combinations of current and voltage across the device, that it can withstand for a certain time before being destroyed. For instance, a power transistor might be rated for 100W dissipation, but that's not the full story. 10 amps at 10V, being 100W, would be OK indefinitely. BUT, 1 amp at 100V would NOT be OK indefinitely, although it is also 100W. That 1A/100V combination can only be withstood for, say, 100 milliseconds, and then it will let out all the magic smoke*. Now over to amplifiers: they also have an area where they will operate as designed. As you noted, drive the level too high, they will clip. Drive too much level in too low a load and they may eventually overheat and break. One common accident on the test bench is full power at 20kHz - not many amps can hold out on that, and of course during music reproduction, they don't have to. But all this is not referred to as 'the SOA' of the amp. * The reason is that at higher voltages, the current tends to hog a small part of the transistor die, so that small spot will heat up much more that the rest of the die. That small spot cannot handle the 100W the whole transistor could handle. It blows. |
Byfwinne, yes I agree. The internal amp Zout is not changed of course. Re: increased 3rd with nfb: that has been laid to rest many years ago. Most people know the (in)famous Baxandall graph showing increased harmonics (even harmonics that were not there without nfb) with increasing nfb. Then, when you continue to increase nfb, the harmonics eventually became invisible again - all of them. There are two sides to this. One, not everybody realised that the worst you could do in this situation, was to use moderate nfb. For lowest harmonics, in this situation (see below), use none, or use a lot! Second, this was a single, crummy FET stage. It has been shown that if you look at this with a whole amplifier rather than with a single crummy stage, the effect is not seen. If you start with a reasonable amplifier, applying nfb decreases ALL harmonics. |
Jan, please re-read my non-tech take 2 or 3 posts north of this post. What you describe is exactly the effect of using NF -- the amp compensates for the output voltage drop based on the amount of NF applied to increase the output voltage to compensate for the interaction of the amp's internal impedance load and the external load of the speakers. The effect is more precisely described as the amp is behaving as though it has low output impedance. So ... the NF circuit does not really change the amp's internal impedance. Instead, it acts like a servo to cause the amp to compensate for the Ohm's Law effects. Of course, as Al, Ralph and others have said, the amp can only do this if it operating within its power delivery limits -- i.e., SOA (safe operating area). Also, there are rarely any free rides. Hence, NF has its own problems, e.g., increased odd ordered harmonic distortion ... and its detractors, e.g., Ralph. IMO, amp designers make trade-offs in order to design and build amps that perform at a certain level at a certain price point. Probably still not saying this correctly, but it goes to show how the terminology can get in the way even though we are all really saying the same thing. |
Just a little background on my experience with the Manley Snappers. I really think what can make a difference is how hard you're pushing the Snappers. I was very concerned about the Snappers - given the specs - which is why I insisted on auditioning them before purchasing them. I had read that they were a tad more sweet in the midrange than the Rogue Audio M-150s (which is what I was planning on after reading some very positive reviews), but I suspected they wouldn't have the power to drive my Aeon i's - especially in the higher frequencies where the Aeon i's can drop down to just under 2 Ohms. And I should tell you that I am also using a pair of subs to augment the Aeon i's since they are totally passive and can only get down to 43Hz. But a practically brand new pair of Snappers came in at my local dealer's shop and he called me up and asked me if I wanted to try them out for a week. I decided to give them a try after speaking with Paul over at Manley Labs - being cognizant of the fact that my listening room is quite small and I would not likely be pushing the Snappers too hard. All I can say is they sounded amazing through the Aeon i's. I brought over two audiophile friends - call them P and W. P is in his late 20's and can easily hear frequencies above 15kHz (which is actually pretty rare) and both were blown away by the sound. We we're comparing the Snappers with my Parasound HCA-3500 which has ZERO problem driving my ML's and the Snappers outperformed the 3500 in practically every way - especially on musicality and sound stage depth. What really shocked me was when W said he thought the Snappers had more slam than the 3500 - especially since slam is what the 3500 is really known for. P indicated that the highs were a bit more subdued with the Snappers, but they sounded much more pleasant in his mind. For W, there was no comparison - the Snappers sounded MUCH better in his mind - even to the point that he has now decided to move over to tubes. And we listened to all types of music - classical (full orchestra and smaller ensemble works), jazz (traditional and modern) and classic rock. Female vocals sounded especially life-like through the Snappers. But keep in mind, the caveat to all this is the levels we were using for the audition given my room size. If you have a large room that needs some serious volume, then all the data does suggest that the Snappers will probably run out of steam and you might be better off with something like the M-150s or M-180's. But in my room at least, the Snappers had plenty of power to drive my Aeon i's with a level of quality that was leaps and bounds above the 3500. Would a pair of M-150's or M-180's do better? Or one of the top-end Pass amps? Maybe. But all I can say is the Snappers were available, they were less than 8 months old and in like-new condition and they were priced at $3600 for the pair (they now retail new for $7200). So in my case at least, getting them was a no-brainer. Specs are certainly important but they are not the end-all-be-all. At the end of the day, you really need to listen and decide for yourself how a component integrates with your existing system and room topology. For me, the Snappers were a major step-up and I'm totally happy with them. |
Thanks Al. My apologies for the numerous typos in my last post. I was typing with my laptop literally on my lap, drinking coffee with one hand and typing with the other hand. Truly a multi-handed effort. That aside, I wanted to say that this has been one of the best threads to get posted in a long time. So kudos to all of the contributors. I believe that if and when I ever change out my speakers or my amp, the terrific comments posted in this thread will make selecting a good amp/speaker combo a less haphhazard (sp) exercise. At the very least, I'll be able to ask better questions ... and know what to expect in terms of getting better answers. Thanks again to all, including of course Ralph, Al, George, Mapman, Unsound and Judy. Cheers, Bruce |
Excellent post, Bruce, with which I agree. I also agree with the first two-thirds or so of the paper George referenced, although I would point out that the author has taken the reasonable step of simplifying the circuit analysis he presents by only taking into account the resistive component of the load impedance. I would take exception, however, to much of the last part of his paper, beginning at the point where he states that: Loudspeakers are not constant power devices. Loudspeakers must have a constant drive voltage to provide a constant acoustic output with changing frequency.IMO (and I feel safe in saying in Ralph's opinion as well), that statement is incorrect and misleading. I would agree with it if it referred to the majority of loudspeakers, rather than being expressed as applicable to all loudspeakers. Many electrostatics being notable exceptions to his statement, IMO. The fundamental error he makes, IMO, is that he assumes that with all speakers flat frequency response in (in terms of voltage) corresponds to flat frequency response out. That will be true, at least approximately, for the majority of speakers these days. However it will not be true for a substantial number of speakers, including many electrostatics. As Ralph has pointed out many times, it comes down to the intention of the designer. Consider the classic Quad ESL-57 George referred to earlier, which is revered to this day (impedance curve shown here). It was designed before solid state amplifiers existed! And it is very successfully used with tube amplification by many audiophiles to this day. Although in fairness I'll say that I recognize that **at least among solid state amplifiers** the vintage Mark Levinson ML-2 which George referred to is recognized as being a particularly synergistic match, and that combination (with two stacked Quads per channel) was the heart of the highly regarded HQD system produced by Mark Levinson's original company (together with a large Hartley woofer and a Decca supertweeter, with a total of six ML-2 monoblocks driving the two channels in a triamped configuration). Regards, -- Al |
Al and Ralph, I read the article that George kindly provided. I also re-read the posts at the link Al provided. I think Al correctly states that there is a bit of friction caused by the use of terminology. I was looking for, but didn't find the post where I coined the terms "synthetic" or "apparent" constant voltage source where negative feedback (NF) is used. I think that using such terminology is useful insofar as it helps one to better appreciate whether an amp becomes a true constant voltage source if NF is used or just acts like a constant voltage source to some extent. Let me explain. My take-away from George's article is that if an amp has an output impedance that is greater than Zero, some part of its power output is being consumed internally, resulting in a voltage drop at the output taps when driving an external load. The author illustrated this effect with some simple examples using an external speaker load of 8 ohms and two hypothetical amps -- one having an output impedance of: (a) .1 ohms; and (2) the other having an output impedance of 2 ohms. The math then follows illustrating how the amp's output voltage and corresponding power output changes under each scenario. I surmise that the terminology confusion comes into play because of what NF does ... and does NOT do. That is, if an amp has an output impedance of say 2 ohms, then as Ralph says, that is its output impedance ... period. But if NF is used, the amp compensates for the voltage drop by increasing output voltage to comepensate, thereby causing the amp to perform like, but not actually be, a constant voltage source amp. As such, with output voltage adjusted to offset the voltage drop at the output taps resulting from the interaction of the amp's own internal impedance and the speaker's impedance, the amp functions as though it was a constant voltage source amp, or like one to a greater extent. But there is always a BUTT. This picks up on what Al, Ralph and the author of the EPDR article have been saying over and over again. Using NF cannot create energy. That is ... an amp using NF will be able to generate power only to the extent it is capable of doing so based upon its internal architecture. Or, as the EPDR article said, within its SOA (safe operatwing area). If the amp operates outside its SOA, it will cut back its power output, clip, become unstable, produce distortion, etc. I said this at the beginning of this thread and I'll repeat it again. I think we are all agreeing with each other much more than not. Butt, I think we are talking past each other. IMO, given that **most** (not all) speaker manufacturers seem to be making speakers with roller coaster impedance and phase angle plots, erring on the side of am amp having lots of SOA headroom and low output impedance is a safe play. That generally equates to a SS beast that can deliver lots of current/power. OTOH, as I said here and in other threads, to illustrate my understand, my ARC tube amp functions within a pretty wide operating corridor like a SS amp, but to do so, requires NF, and a massive power supply. Or using my own terminology, my amp performs like a "synthetic" SS amp, to some extent within a large "SOA." Hope this helps ... butt it probably doesn't. |
Ralph and I and others discussed his views on the relation between feedback and output impedance in this thread. It essentially comes down to a matter of terminology. Regards, -- Al |
Output impedance does go down with nfb - that's a basic tenet. Easy to check: take a non-nfb amp and change the load d from 8 to 4 ohms. You will see that the output voltage drops a bit. Now apply nfb, do the same thing and you will see that the drop is less, showing that the output impedance has dropped. In fact, it drops exactly with the feedback ratio. Apply 20dB nfb and it drops by a factoe of 10. Of course we all know that Zout is not physically a resistor or sumptin'.... Jan |
04-04-14: Atmasphere : George, this may come as a surprise but increasing feedback does not affect output impedance. It stays the same, and the proof is simple. Oh yes it does Ralph it may supprise you even more, as I can show from many many others even smarter that all here put togther also on the net, as this one sample below, from your OTL opposition, Bruce Rozenblit of Transcendent Sound. Just read at the bottom of the page under, Single Ended, Push Pull, OTL and the conlusion all highlighted for your easy reading. The same also applies to SS amps. http://cc.bingj.com/cache.aspx?q=negative+feedback+transcendentsound&d=4590165989524871&mkt=en-AU&setlang=en-AU&w=VZvSRMth7T4nXfW-P63Cwy4N-Vhpuv2m Cheers George |
If one looks at the Zeros as a type of adapter, its not that complicated to determine the value case by case, which will vary widely. Some cases they will add value, but only when an adapter is what is needed to make two devices not designed to work well together work well together. But clearly if starting from scratch, in most cases, one will be better off NOT using an adapter, especially one that costs big bucks in order to bridge a gap. FRom the perspective of an amplifier vendor whose product plays by a different set of rules than most, there are surely many good applications of the adapter. However, if speaker maker and amp maker play by the same set of rules, there should be no need for an adapter if they dd their job well. IF they didn't, they will probably go out of business and no adapter will help save them. |
With a measured damping factor of 4.7 and an output impedance of 1.5ohms it's closer to an 8ohm tap than a 4ohm tap. George, this may come as a surprise but increasing feedback does not affect output impedance. It stays the same, and the proof is simple. Your assertion that they "solve a problem" is correct, technically. But at the cost of sound quality. If sound quality is not a priority, then sure, buyers have indeed got their mismatched components to "work" together. But only that. The degradation of sound quality is obviously secondary to them. As a manufacturer, I would have thought your emphasis would be on making sure your amplifiers were matched with speakers that show them at their best ? Surely you're doing your products a disservice, by suggesting the Zero's as a bandaid panacea for buyers ? Tradeontheweb, sounds like you and I are more on the same page than different. Whenever someone calls me and is interested in one of our amps I always ask about their loudspeakers to see what I am up against. Sometimes they have speakers that they don't want to sell that are IMO not all that compatible. Sometimes they won't work even **with** the ZEROs. But if they will work, I suggest them. Quite often they ask 'doesn't that defeat the OTL aspect of the amplifier?' to which the answer is 'No.' That is because the ZERO has such a low turns ratio due to its only going from 16 ohms down to 4 ohms or so. It also does not have to block DC; between the two that gives it more bandwidth than most amps. You have to start with an amplifier that already has a low-ish output impedance and puts out no DC... People also ask if it degrades things as you allude to, the answer to that is "The ZERO is a problem solver and there will be no tradeoff whatsoever, if not it is either not being used properly or does not need to be used at all." Now its the former in that last statement that needs some looking into. For example, you can set the ZERO up to run only a certain portion of the loudspeaker. An example might be a speaker that has a 4 ohm woofer array but is 8 ohms in the mids and highs, and the speaker can be bi-wired. In that case you can recover some of the lost impact in the bass by using the ZERO only on the woofers. There are those cases where a person has a speaker that is so inefficient and/or with an adverse impedance curve that there is nothing for it; then I let them know that:
The ZERO only comes in when it is obvious that a person is simply not going to budge on their loudspeakers and that is that. Again, the ML ESLs have a very low impedance as they want more of the solid state market; to use them successfully with tubes the ZERO is an excellent option. The reason for this is simple- a tube amp using a set of ZEROs still has an excellent chance of sounding better than transistors for all the reasons that have been debated about tubes and transistors in the last 50 years. The ZEROs don't change that. |
All depends on which way you look at it Al. Saying it's "optimised" for a 5ohm speaker does not mean it's a 5ohm tap. But giving figures as exact as in 1/10th's, 4.7 for damping and 1.5ohm for output to me is far more exacting. And from these two figures the tap is closer to an 8ohm tap than 4ohms. Whatever the case, the way your seeing it, or me, it's not the ideal amp for what the OP has. Cheers George |
George, the 4.7 number appearing on that page is a specification, not a measurement. On the same Manley page an output impedance of 1.5 ohms is specified, which is confirmed by TJN's measurements in the review you linked to. On the same Manley page, and also in the manual, the statement "optimized for 5 ohms" appears. Maximum output power, input sensitivity, and frequency response are all specified for a 5 ohm load. The 5 ohm power rating is higher than the 8 ohm power rating, for the same distortion level. I see no reason to assume that the 4.7 number is accurate and the 5 ohm number is not. As I said, the converse seems much more likely. Regards, -- Al |
From here Al. At the The Manley website. http://www.manley.com/msn.php Features and Specifications Manley Snapper Damping Factor: 4.7 Cheers George |
OK Almarg, I'll split hairs with you. With a measured damping factor of 4.7 and an output impedance of 1.5ohms it's closer to an 8ohm tap than a 4ohm tap. But all this can change with a bit more global feed back to raise the damping factor and lower the output impedance. But then Audiophiles don't like the idea of too much feedback, so throw a Zero on it for difficult loads like these speakers the OP has and maybe be happy??? Cheers George |
Thanks George. I looked at the review and picked up the following concluding statement that "[t]he Manley's output impedance [1.5 ohms], while not unusually high for a tube amp, is still high compared with typical solid-state designs, and may therefore have some effect on the frequency response of the speaker-amp combination.Thomas J. Norton" The reason I asked the Q is because Capdek said that the Manley does a good job with his ML ESLs. I'm sure Capdek has good reason to be happy with his Manley/ML combo. But I suspect that the treble may be a tad shelved and the bass a bit augmented -- just based on what Thomas Norton said above. Obviously, unless one measured the ML's frequency response in a controlled environment, it's difficult to know what's really going on with Capdek's rig. So, I'll leave it there. If Capdek is happy -- then that's all that matters. This has been an interesting thread. I think all of us have leaned a lot. |
George, if I may be a bit pedantic as well, although multiplying the 1.5 ohm specified and measured output impedance by the specified damping factor of 4.7 ohms equals 7 ohms, both the manual and this page at the Manley website clearly state that the output is optimized for a 5 ohm load. As I indicated the numbers are not quite consistent, but I would be inclined to think it more likely that the damping factor spec is inaccurate than the 5 ohm figure. In part because I note that the damping factor number does not appear in the manual, but the 5 ohm figure does. And also because maximum power ratings are provided only for 5 ohms and 8 ohms, not 7 ohms, with the 5 ohm capability being higher than the 8 ohm capability. Regards, -- Al |
Hi Unsound, The Manley Snapper has a single output tap, which is described as having been optimized for a 5 ohm load. Its output impedance is specified as 1.5 ohms, as George indicated. Its specified damping factor of 4.7 is slightly inconsistent with that (8 ohms/4.7 = 1.7 ohms; 5 ohms/4.7 = 1.06 ohms), but is in the same rough ballpark. You might be recalling having read something in which the author confused the output impedance of a tap with the load impedance the tap is optimized for. A not uncommon error. Best regards, -- Al |
Snapper measurements by Thomas Norton http://www.soundandvision.com/content/manley-snapper-monoblock-tube-power-amplifier-measurements |
Atmasphere. I have indeed used the Zero's on many occasions, as I mentioned in my post. So my opinion IS based on experience, not on any wish to derail this thread, as you insinuate. My experience with them was as I indicated - yes, they allow amps that would otherwise struggle, to drive speakers that present too hard a load for them. An analogy would be saying that your standard 4 cylinder commuter car is capable of 200+mph. But only when towed by a Nascar ! Then claiming that there's no difference in the experience vs not being towed. By their very nature, the Zero's must add/subtract something from the sound. I'm sure their are many happy Zero owners out there. There must be, as they sell. But, I suspect those owners would be better off educating themselves, then spending the money on a better matching between components in the first place. I have yet to hear a system that benefitted (sound-wise) from their use. Your assertion that they "solve a problem" is correct, technically. But at the cost of sound quality. If sound quality is not a priority, then sure, buyers have indeed got their mismatched components to "work" together. But only that. The degradation of sound quality is obviously secondary to them. As a manufacturer, I would have thought your emphasis would be on making sure your amplifiers were matched with speakers that show them at their best ? Surely you're doing your products a disservice, by suggesting the Zero's as a bandaid panacea for buyers ? Just my 2c worth ! |
Bifwynne, the Manley Snapper from the website looks as though it has 1 set of 8ohm speaker terminals?. It states in the specs that it's damping factor is 4.7 (into 8ohms?) which would mean it's output impedance is around 1.7ohms. If it's a 4ohm tap which I doubt, then the output impedance is .85ohm. Cheers George |
Atmasphere, 04-03-14: "...George keeps pulling the thread off-topic by suggesting that a powerful transistor amp be employed; he also said that my suggestion of the ZERO was 'stupid', and did so without any experience whatsoever with their use...." Georgelofi, 03-19-14:"...I have Ralph, and I stand by what I said, I have even put them on my system which definitely doesn't need them, and the sound took a big step backward...." |
I certainly did not derail the topic Atmasphere, the OP asked for suggestions for tube amps to go with his Martin Logan speakers. I simply mentioned in my first post that they are a difficult load, no mention ever of him getting a SS amp ever, you are seeing things. It was you Atmasphere that started spruiking on about the Zero from your first post, instead of guiding the OP correctly to a suitable amp. It was also you Atmasphere that said, "that others said", (never implicating yourself) that the Zero is beneficial to all amps "even good solid state amps" into these kinds of loads. You call me a troll twice now. Be careful Atmasphere, It almost looks like your shilling for the Zero, because your amps are the ones that need them the most, and visa versa, the Zero's need your amp's the most. as this quote from Paul Speltz from a TNT review of the Zero's "Paul Speltz, a devotee of OTL amps, decided that he wanted to use his favourite DIY speakers with his OTL amp, but the nominal speaker impedance of 4 ohms wasn't a good match for his amp. With these thoughts in mind, Paul designed the ZERO Autoformer" And then this quote from the TNT reviewer on the Zero's with amps that don't need them. " The most important thing to remember about the ZERO Autoformers is: if there is no significant impedance mismatch, then there will be no real benefit to using the ZEROs. For example, when the Autoformers were connected as an impedance multiplier to a pair of B&W DM602 speakers there was little benefit for most tested amplifiers. In fact, the Le Amps and B&W combination sounded a little too bright with a strident sibilance that was distinctly irritating." As I've always stated the Zero's add their own set of problems that can be clearly heard when the amp/speaker combo does not need them. (as the above reviewer found) And to suggest they are beneficial for all amps into hard loads is an absolute misguided quote. They are a bandaid fix for owners that do not want to change their amp or speakers so they are compatible. Cheers George |
Again two different perspectives on how to get a good amp/speaker match. To me the point is zeros are the best solution for ML with many tube amps. If you match up amp and speakers directly, zeros not needed. Perhaps an "adaptor" would be a better technical term for what the zeros are. They would make for some fairly pricy "band aids", though the argument could be made that an adapter is a technical form of "band aid". Its mostly just semantics, some more agitating to some than others. |
I recently auditioned a set of Manley Snappers with my ML Aeon i's and the combo with my ModWright SWL 9.0SE sounds absolutely superb! The Snappers are 100 WPC monoblocks that run in ultralinear mode - they are very tight and detailed in the lows and highs with no boom or grain and the midrange is to die for. They pair exceptionally well with the ModWright which is a very transparent tube-hybrid design. I have a fairly small-sized listening room and the Snappers have plenty of power to drive the Aeon i's - even for demanding rock and full orchestra pieces. Depending on your listening levels, I would highly recommend the Snappers as being a great match for MLs. |
Tradeontheweb, the ZERO does not affect the sound quality as you and George suggest. How it actually works is that many tube amps have problems on ML speakers. In such cases, they are not going to work very well. The ZERO solves that, plain and simple. Nor is it a bandaid- it is however a problem solver and this is a classic case of the kind of problem it was designed to solve. And just FWIW, I don't make a dime when Mr. Speltz sells a set of ZEROs and he sells them to more than just customers of ours. This thread was established to ask the question of what tube amps will be suitable for ML speakers. A few will work fine without the ZERO, but many will not, and the ZERO represents a practical solution so that any amp with enough power otherwise can do the job. George keeps pulling the thread off-topic by suggesting that a powerful transistor amp be employed; he also said that my suggestion of the ZERO was 'stupid', and did so without any experience whatsoever with their use. Its true that I sell amplifiers, and its also true that I have a lot of experience and feedback from people who use the ZERO. I hope its OK if I walk the talk. We can be pretty sure that George does not- he is just here so far as I can tell to derail the topic. That is one of the ways you can identify the activity of a troll. Now if you think that I should not be posting here because I sell amplifiers, that's fine, again just FWIW audio happens to be a hobby of mine and I like it. That is the reason I am here- and I have tried my best to help out people whenever I have found that my experience was useful (I started my career in 1974 repairing consumer electronics at the local Allied Radio service facility, where I got a lot of troubleshooting experience repairing all manner of tape machines, car stereos, receivers, tuners, shortwave radios and the like- that was how I put myself through school.) So to answer your question, In A Perfect World, of course its 'way better to start with a good match, in that way you and I totally agree. But here is a little experience tidbit for you: over the last 30 years or so of business, I have found that you can recommend that till you are blue in the face and people will still go right ahead and put an amp and speaker combo together where it is really obvious that it is not going to work, for the simple reason that they like the speaker, and they like the amp and they want both at the same time. People wanting to put a tube amplifier on a ML ESL is an excellent example of that. **That** is why the ZERO is handy- you can have your cake and eat it too, and it allows for excellent performance (for example the ZERO has bandwidth from 2Hz to about 2MHz, which is wider bandwidth than most amplifiers...). |
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 matched amp/speaker combos, they are a big step backward in sound quality. They are, as George puts it, a bandaid fix. For people who have a mismatched amp speaker combo that cannot be driven correctly, yet have no desire to change either and fix the mismatch correctly. They can live with what they have using the Zero, but they will then introduce another set of problems that affect the sound quality. Is it worth $1140 for a bandaid fix??????? Or should they fix the mismatch problem, that is the real question???? |
