Tube Amp for Martin Logan Speakers

Hi, I love tube sound through my Martin Logan Aerius-i fronts and Cinema-i center. I currently have a Butler 5150 which is a hybrid, but it busted on me and would cost $700 to fix. I've had china stereo tube amps that were pretty good and gave true tube sound, but not enough drive for higher volumes. I live in condo, so not like I can blast music anyways but still. I got the Butler because I wanted 5 channel tube sound for home theatre (The piercing sound from my Denon 3801 receiver was not pleasant to my ears). It appears there are only three multi-channel tube amps around, from Mcintosh, Butler 5150, and Dared DV-6C. The latter two are hybrids, and the last one was one of the worst tube amps i've ever heard. I have no clue why 6Moons gave the Dared a 2010 award, but maybe it's because it produces only 65W.

So since multichannel tube amps are hard to come by, and they tend to be hybrid, I was thinking maybe it would be best to get three true tube monoblocks to power my fronts. Thing is I wonder if they will be underpowered for my speakers, and not sure which ones are decent for the price. Maybe China made ones would suffice, and they still go for pretty expensive price. I'm wondering if anybody knows of a decent powerful tube monoblock that is affordable, because I can't pay $3000 per block. or maybe best to just repair my Butler. Thing is, I'm not confident that it is reliable. The tubes are soldered in which is weird, and i've taken it to a couple repair guys who both said that the design is not good, because it's very tight inside and more susceptible to being fried from DC voltage areas. it's too sensitive.

Any suggestions for tube monoblocks, even if china made ones? the holy grail for me would be Mcintosh tube amp, but they are hard to come by. Thanks.

Hi Smurf, your Aerius-is are getting a little long in the tooth too. Maybe you could fix the Butler and then save up for a whole new setup? The new Martin Logans sound really nice.

People recommend the usual wide variety of tube and solid state amps for MLs. Some people swear by ss, others by tube. PrimaLuna make nice monoblock tube amps that many people feel work well with MLs. I don't know if they fit in your budget or have enough power for you, but they would be worth checking out.
Just purchased the Primaluna Prologue 7's. I was using a Bryston 4B-SST. The prima's are smoother and much deeper and wider soundstage. I am using them with a pair of Martin Logan Ethos speakers and the match is a good one. Plenty of power to run these speakers. I highly recommend these amps.
take a look at the consonance cyber 800 mono blocks.
I use a pair of Quicksilver Mini-Monos (25 watt) on my ML Electromotion ESLs. I'm using the subwoofers crossovers to take some of the load off the amps. It plays loud enough for me and it will play loud enough for condo use but it is at the very limit. If you play louder than me it might not be enough. Quicksilver makes a 40 watt Mid-Mono amp and that may be just what you need. The Quicksilvers are very nice sounding amps and I would never consider selling them, they are that good.
Are you sure it's not worth it to fix the Butler?
"Everything you have, you owe to that Butler."
-Oprah Winfrey

Sorry, I couldn't resist.
Maybe get a stereo tube amp for your Aerius's and a SS mono amp for your center. I'm not too into HT, but one thing I have noticed is that it is often hard for a center channel speaker to keep up with the L&R fronts. Giving the center a more powerful SS amp may sound better for theater and the tubes on your main fronts will sound better for music.

I had the SL-3's and had no problems with tubes. Yours should be easier to drive than the ones I had. An ARC VT-100 was a great match, but I ended up using my VAC 30/30. If SS is not out of the question, you would probably like a Pass Aleph 0 (if you can find one). A 5 might be easier to find, but its not quite as good. The 3 won't have enough power.
The ML Arias dip to between 3ohm and below 2ohm between 10khz and 20khz with a not so easy phase angle of -35degrees.

This says to me you'll need an amp that is happy driving a moderately hard load.

If the amp cannot handle that load happily, it may start to sound a little rolled off in the top end as power droops off, compared to what it's doing down lower in the frequency.

eg: it will act like a bit of a fixed tone control, instead of being flat from 20hz to 20khz.

Cheers George
Check out Quicksilver audio. Mono amps are all he makes.
I ran ML requests for years with a CJ premier 11A and thought I was very happy. As funds allowed I up graded from the 11 to Premier 8a's (70 watts to 275). I never realized how much music I was missing especially at low volume. Bottom line, the more power you can feed the ML's the better.
The trick with Martin Logans is that quite often if you have a tube amplifier, you will want something like a set of ZEROs ( to help the amp drive the really low impedance of the speaker, particularly at high frequencies.

ML has been trying to get their speakers to work with transistors; to this end they have kept their impedances low. The problem with this approach is that ESLs and tubes have been the match made in heaven since the 1950s- you put transistors on the speaker and brightness is the name of the game. So it you want to use tubes, you have to deal with the impedance and that is what the ZEROs are for.

What's the difference between an output transformer and an autoformer? Also, as most tube amps are not OTL's, is there a drawback for having both in the chain? I always thought autoformers did pretty much the same thing as OT's.
Zd542, I was tempted to take a shot at your question but decided not to. Ralph (Atmasphere), Al (Almarg) and several other members are EEs and will do a much better job responding.

Having said that, I will just put out there this simplistic explanation. An autoformer raises the speaker impedance presented to the amp, or perhaps it might be better said, that the device makes the amp think the speaker impedance is higher than it actually is. There's a white paper on the Autoformer web site. Just do a search.

I'll anticipate you next question which is why can't one simply insert a resister in series with the speaker. I think the answer is that it will draw off a lot of watts as heat and will make the output impedance of the amp look higher, thereby screwing up the DF. It may also affect bandwidth ... and there I stop.

Looking forward to reading a better explanation from the EEs.
Bifwynne, if you installed a resistor to raise the impedance of the load it would certainly absorb power. That is why you use a transformer, in this case an autoformer.

The reason the ZERO is an autoformer is that it does not have to block DC, which makes it simpler and better performance (wider bandwidth). The ZERO has wider bandwidth than almost any amplifier made, tube or transistor.

The second thing about the ZERO is that the amplifier already has a lower output impedance, its not like 3000 ohms or something, instead we are simply going from 16 ohms down to 4, 3 or 2 ohms. With such a low resulting turns ratio again greater bandwidth is possible.

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. If sound **pressure** is your goal then you have a weak argument for lower impedances, if you have a solid state amp capable of supporting that lower impedance properly; not all do.

This is where the ZERO comes in- for those speakers that unfortunately are lower impedance due to poor design choices on the part of the designer (I added that last caveat because that is precisely the problem), the ZERO is a problem solver. Certainly it will help a smaller OTL drive such loads, but it will also help transistor amps that might seem perfectly comfortable on 4 ohms to actually sound better (although with less power). IOW, a transistor amp will sound smoother and more detailed when driving a higher impedance (due to making less distortion)- enough so that there can be a benefit to using the ZERO for that reason.

Paul Speltz, who makes the ZEROs, has a letter from Steve McCormick describing this.

I don't see the ZEROs as obviating the 'OTL sound' either. As I mentioned earlier, the ZERO has very wide bandwidth, wider than any amplifier; it would not be possible if it had to block DC or work with a high impedance input!

If speaker designers ever sort out how the load affects the distortion produced by the amplifier then we will see higher impedance speakers and no need for the ZERO. But I suspect that day will never come, so the ZERO will continue to be quite useful as a problem solver for those prefer sound quality over distortion.
Ralph, ... if a speaker has a rock and roll impedance curve that varies from 4 ohms to 20 ohms as a function of FR, would using a ZERO to double the impedance, say ranging from 8 ohms to 40 ohms, cause a Voltage Paradigm amp (i.e., a SS amp or low output impedance tube amp) to choke driving such a speaker?
Once again I disagree with Atmasphere's oft-repeated assertion.
03-17-14: Unsound: Once again I disagree with Atmasphere's oft-repeated assertion

Agreed, I have yet to listen to a Zero Autoformer that has worked without causing other problems.

A simple way to hear what they do wrong, is to put one between an amp that has no problem driving the speakers/load with out it.
Then you will hear what they do wrong with it in.

In my view they are a bandaid fix to allow an amp that has no chance of driving the speaker by it's self, to make it usable with that speaker. And I use the word usable lightly.
Far better off getting the right amp for the said speaker to start with.

Cheers George
I ran Martin Logan Aerius-i with an Audio Research VT60 on the 4 Ohm taps and it sounded great (wish I would have never sold that amp) and I listen fairly loud. At the time I also had a Bryston 3B and believe it or not, the ARC gave the percerption of similar power (same sound level at the same Pre-Amp volume position) and the ARC was smoother with a larger sound stage. Of course it got hot (especially the output transformers) but it never bothered it.
I take it Unsound, that you are an advocate of increasing distortion :) Because by disagreeing with me, that is exactly what you are doing.

Let's try that on for just a moment. Usually in high end audio we are interested in getting rid of colorations and just having a neutral presentation; the fact that equipment does have colorations sparks a lot of conversation as we both know. We also know that the ear translates distortion into tonality- for example the 2nd order harmonics make tubes amps sound more lush.

So what you seem to advocate is to use a lower impedance loudspeaker, as the amplifier will certainly be more distorted. Because that *is* what happens. You can see it in the specs of all amplifiers in existence. None have decreased distortion with decreased impedance. So the only conclusion available to me is that you seem to want the amp to sound more distorted. If you are all like 'no, that's not me, why are you putting words in my mouth?' then you and I are on the same page, which means that you do indeed want to get the impedance higher as that will reduce the distortion coming from the amplifier.

George, take a take a look at the links on this page:

Paul Speltz has a letter from Steve McCormick, stating that his amps (which can drive 4 ohms effortlessly) sound better driving 4 ohm speakers through the ZEROs. The reason is simple: distortion is lower. That translates to 'smoother, more detailed' as far as the ear is concerned.

Bruce, what will happen in the scenario you describe is that the amplifier probably will have a problem on the higher impedances. Voltage Paradigm amplifiers often do. However, if that amplifier happens to also use tubes, it will do better into the higher impedances than a transistor amp will.
^A lower impedance can help; extend frequency response, improve the linearity of frequency response, and as you've already noted can increase dynamic range.
If autoformers were such a panacea, why don't more (any?) speaker manufacturers include them in their products? If not speaker manufacturers, why don't more (any?) cable manufacturers, especially those that like to add such boxes to their products, terminate their offerings with them? I wonder what % of people that have audio gear incorporate autoformers in there systems? I'd hazard a guess that it's quite low.
One letter from one amp manufacturer (even one I respect) that might suggest that his products sound better into higher impedances, does not convince me that pros of higher impedances don't outweigh the cons. IME, I seem to prefer systems with speakers that have lower impedances over those with higher impedances. Now I don't go looking for these things, but a pattern has emerged. With this I can only come to a hypothesis that the distortions you make mention of; are less significant than the other considerations that come into play towards all that makes listening enjoyable.

I've had numerous ML's as well as other stats for 2-ch and HT. I use tube amps exclusively with stats. Back in the 90's, I had the Aerius. I found that the VAC PA 90 monoblocs were magic with them. Many VAC amps work well with stats. I saw a pair of VAC PA 90's on Agon a couple days ago. Kevin Hayes, the designer has King Sound speakers, a very difficult load, and uses his VAC phi 200s with them. Maybe consider a stereo unit now and add another later. Good luck.
Atmasphere: George, take a take a look at the links on this page:

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.

They are sometimes a "recommendation" for OTL's as they allow them to drive speaker that would not otherwise be a good match for. Best off changing the amps or the speakers.

""They are a bandaid fix to allow an amp that has no chance of driving the speaker by it's self, to make it usable with that speaker."

Cheers George
I had many stats and tube amps through the years including four pairs of ML's. I had the Aerius-i in the 90s. I paired a VAC PA 90 with the Aerius. It was a magical combination. Since then I've used other VAC amps driving stats with great success. They're designed and built to do it. I saw a PA90 on Agon a couple days ago. Another thought may be to consider the VAC Phi200 stereo amp now and get a second one later - if needed. FWIW - Kevin Hayes, VAC AMPS president and designer uses the PHI 200 to drive King Sound stats. Good luck.
George, you took the quote out of context- sounds like you didn't read the article to me.

Unsound, I have a number of friends in the industry that make transistor amps. When Steve's letter turned up, I asked them about this and their response (paraphrasing) was:
'Just because the amp can drive a lower impedance with more power is not the same as saying it is also sounding its best.'

Now there is no argument that supports your position that because the impedance of the load is lower, that this translates to
extend frequency response, improve the linearity of frequency response, and as you've already noted can increase dynamic range.

Of the latter point 'dynamic range' you are putting words in my mouth.

But given your response (and apparently also that of George) it does indeed appear that the both of you prefer to have your amplifier add some distortion. So in that regard we do indeed differ- I prefer a lack of distortion if possible.
I'll agree that benign speaker impedance curves makes it easier to find an amp that is likely to sound really good with said speakers.

But lower and more challenging impedance curves are more the norm these days, and with just a little care, one can find many amps that are good matches. Class D amp technology pushes this truth even further than before, and makes smaller more efficient packages that perform well possible.

SO choose your approach wisely and listen to the results and there are multiple paths to happiness.

There are always so many types of distortion at play in any reproduction, that focusing on any particular type does not tell the whole story nor add much value IMHO.
Wow I want to thanks all who have responded, much appreciated. It looks like monoblocks are too expensive and means id have to power each one on manually. I know you can get some unit to power things on but I'd like to have the simplest solution with acceptable warm flat sound. A good solution might be to get stereo tube amp for the fronts and just use my denon for centre and rears. Just wish there were more multichannel tube amps, because then the sound from 5.1 would be more even between the speakers but I guess it would be too massive in size and not as reliable.

I spoke to a reputable amp repair guy I'm my area and he says that warm sound can be had from SS by maybe replacing some parts. Says that tube amps are not reliable as most have to be hybrid in order to dish out a lot of power. I'm not very technical in this aspect. All I know is that with my denon 3801 with about 150w or so at 4ohm and listening to Chris botti 5.1, when Yo Yo Ma begins playing, the cello doesn't sound as deep and full as when I was using the butler 5150 with 225w. With the Dared multichannel hybrid at 65w per channel. it was even worse. The repair guy suggested get affordable parasound SS and make some relatively cheap mods, as he says the design is decent and easier to repair than other brands.
I could repair the butler locally and add sockets for the tubes for easier maintenance. I'm just not too confident in its reliability. Seems that it's very sensitive and can blow if moving it around or playing with cables. The other option is send back to butler so they fix back to original spec but that would probably cost more than 700. a lot cheaper than getting monoblocks, and about same price as getting a used SS amp.

I've read that martin logan have demo'd their speakers with parasound which apparently has warmer sound as opposed to say lexicon and nad amps, so maybe should look into that.
Im shocked at how much tube monoblocks go for new. I don't get how it is justified for makers to charge 3000-10000 for such a small thing. Compared to SS amps that are massive and with more parts. I guess tube monoblocks have solid gold power sections or something.
Tube amplifier power has always been more expensive (the tubes themselves cost more, the filament circuit to light them up costs something, so does the output transformer). It was the reduced cost of transistors that got the industry going in that direction in the first place.

Class D has added another order of magnitude to that.
Ralph: why not just put some output transformers on your OTL's so they can drive these types of loads then, instead of this band aid fix of the Zero's

Or the owner can do one of two things to fix the problem.
1: Is to get the right amp to drive said speaker load.
2: Is to get the right speaker with a load so amp can drive it.

And the suggestion to put this Zero transformer on a tube amp that already has an output transformer is one of the worst ways of fixing/masking the problem.

Cheers George
Yeah different technology but still seems like companies are ripping people off with tube monoblocks. If $10000 each and you need two, I'd rather get $18000 gold bar to hang around my neck and $2000 used amp haha
I'd have the $18000 gold bar drawn into wire and sent it to JD (Jadem) to make me a full cable loom:)
Nice ISO hehe. I just think there better be gold in thems monoblocks to justify the super high price. Tubes $300-400, circuit boards and wiring $20, power transformers $1000, metal case $100. Where is the rest of the 15,000 going to?
Atmasphere, on this very forum speaker builders have suggested that with a lower impedance they can more easily achieve deeper bass response (extended frequency response), a more linear impedance (improve linearity of frequency response)and as you've said a lower impedance can make a speaker play louder (increase dynamic range)(am I really putting words in your mouth?). To that let me add that I've yet to see an impedance plot from a speaker that claims to provide waveform fidelity and can back it up with an appropriate square wave response that doesn't also demonstrate an impedance plot that drops below 8 Ohms. Now any deviation from what the medium can offer with regard to any of the above would be a distortion. We haven't created the perfect speaker or the perfect amplifier for that matter yet, they all come with distortions. Pick your poison. As has been previously posted on this forum that the vast majority of speakers rated and listed in Stereophile as being worthy of their highest Class A rating have lower impedances. It appears that the most successful high end speaker manufacturers make speakers with impedances that drop below the 8 Ohm standard. I suspect that the majority of readers here on Audiogon have speakers that drop below the standard 8 ohms. Do we all like distortion too? As I've already alluded to, I don't go out of my way to find speakers that have lower impedances, it's just that the systems that seem to more totally satisfy me have speakers with lower impedances, regardless of whether or not the amplifiers do or don't have some academic distortions that don't seem to bother me as much as the alternatives. Please pardon me for butchering a cliche', but it comes down to hearing the forest from the trees.
on this very forum speaker builders have suggested that with a lower impedance they can more easily achieve deeper bass response (extended frequency response), a more linear impedance (improve linearity of frequency response)and as you've said a lower impedance can make a speaker play louder (increase dynamic range)(am I really putting words in your mouth?). To that let me add that I've yet to see an impedance plot from a speaker that claims to provide waveform fidelity and can back it up with an appropriate square wave response that doesn't also demonstrate an impedance plot that drops below 8 Ohms.

You are indeed putting words in my mouth. What I said was that a lower impedance can sometimes get you more power out of some transistor amps. That is a long way from saying that is is increased dynamic range! For example the speakers I have at home are 98 db, go down to 20Hz, and are 16 ohms. They tend to have dynamic range because of their efficiency, which is where dynamic range actually comes from.

Regarding the other point you made in the quote above, a link would be nice. I can't think of a mechanism that would give a speaker with lower impedance an advantage of better LF response. The two are unrelated: you can get exactly the same LF response from a speaker that is 16 ohms or 24- impedance has nothing to do with it.

George, unlike Unsound, you are a troll. Your comments are unwarranted, without merit and uncalled for.
^Let's start with these links 1st:

"If sound quality is your goal, it will be best served by a speaker that is 8 ohms or more, all other things being equal." If you want greater **sound pressure** there is a slight argument for 4 ohms if you have a transistor amp. IOW, there is no argument in support of four ohm speakers in high end audio.

FWIW these days there is little argument for 4 ohm speakers in high end audio. This because regardless of the amplifier technology (transistor, tube or class D), the amplifier will sound better and perform better on higher impedances. Of course, if you are unconcerned about sound quality, and more interested in sound pressure, than 4 ohm speakers will be more attractive if you also own a solid state amplifier. The other argument against 4 ohms is the speaker cable- they are extremely critical for best results on 4 ohms, while at 16 ohms they are not nearly so. Making a speaker to be higher impedance, all other things being equal, is an easy way to make the speaker appear that it is smoother with greater detail, always a desirable combination.
Atmasphere (Threads | Answers | This Thread)

The point is; speaker designers have to make many considerations when designing speakers and sometimes for the greater good compromises have to be made, and rarely is it so black and white that a design choice is either good or bad. Even what might appear to be a less than ideal choice might actually have some positive attributes.

BTW, I don't agree with your assessment of George either. Like most of us here, he's shared his experience and his points and advice seem to have merit.
"Im shocked at how much tube monoblocks go for new."

Its a reasonable response I think.

Especially in the case of low power tube amps like SETs costing 5 digits. These use only a few tubes, and often claim to keep circuitry simple towards the end of good sound. Granted, high quality parts cost more and there is some intellectual value associated with design, but nothing hugely innovative going on here.

OF course, more tube power = more tubes, so understandable how cost goes up in that case.

If you buy into the concept that a couple of watts can be made better than if more, then that helps with the justification. But then it often requires very expensive and large speakers to complete the deal for TAS.

I tend to think you get a better deal with quantity, including watts, and those additional watts are not as detrimental as some purists might portray them to be on the grand scale of all the things that go into good sound, especially when modern SS amps like Class Ds are more efficient and cost effective than ever before.
03-21-14: Atmasphere:George, you are a troll. Your comments are unwarranted, without merit and uncalled for.

There is only one reason for you calling me a troll, that is you have to stick up for the Zero Transformers, because they are the only way your OTL's will drive many semi difficult speaker loads that are out there.

And I stand by my comments about them, they are a bandaid fix for amps that cannot drive difficult loads, and the owner is better off getting the right amp, or an easier load impedance speaker.

I have actually praised your OTL amps, when they are mated to the right speaker, but to put a Zero Transformer on them is just defeating the fact they are OTL in the first place.

Then your suggestion of putting a Zero on a tube amp that already has an output transformer is just plain stupid, instead of getting the right amp or speakers. And then to infer to putting them on a good quality solid state amp is just ****************

Cheers George
Atamsphere, here's another link:

12-28-09: Audiokinesis
Unsound, obviously I should have
made it clear which part of my
response was about things an owner
of existing speakers could do, and
which referred to something that
would have to be done during the
design stage.

In my opinion using an autoformer is
something a speaker owner would do
to make his speakers more compatible
with OTL amps.

If we're just looking at the design
stage, then yes it is easier to
smooth the impedance curve by
lowering it. But if the end goal is
compatibility with OTL amps, for
example, lowering the impedance
curve can be counter-productive.
Some of the design choices that lead
to a medium to high, and smooth,
impedance curve need to be made
before the crossover design stage.
For example, I can't expect to build
a 2.5-way system using two 8-ohm
6" woofers and end up with an
OTL-friendly design.
Audiokinesis (Threads | Answers |
This Thread

I'll try to find more as my time
Ralph, George and Mapman .... I have no dog in this fight, but I have read the several posts and would like to suggest that much of what everyone has written has merit. Let me suggest to my fellow hobbyists that you aren't really disagreeing with each other, but you are talking past each other and just getting frustrated.

I think Ralph would agree, and has said as much in other threads, that a high'ish output impedance amp might not mesh well with a low'ish sensitivity speaker that has a roller coaster impedance curve. Indeed, one could expect sonic colorations as a result of the interaction between the two components behaving in according with various electrical principles, e.g., Ohm's Law.

That may be why Ralph says that an autoformer might aleviate some aspects of the "non-optimal" (whatever that means) impedance match in such cases. George, I gather your point is that sticking an autoformer into the circuit is just a "patch" for an underlying issue that maybe shouldn't be an issue in the first place.

If that is a fair restatement of your view, I too happen to be biased (pun intended) against sticking gizmos into the circuit based on a few anecdotal experiences of my own. In the two or three cases I put "artifacts" into the signal path, I had dismal outcomes. I am not saying one would have a similar result with autoformers. Just that I am dubious based on past experiences. And even if they work, I am not sure I would want to shoe-horn an amp and speaker together if the two components weren't a good fit in the first place. But that's just me.

If we can all agree that I fairly restated the dilemna, let me suggest that perhaps one way to view OTL amps is kinda like SETs. That is there are audiophiles who swear by SET amps. But, ... they recognized as a threshold matter that a SET amp will not be a good match with a low sensitivity speaker that has a roller coaster impedance curve. That's why some have suggested matching a speaker like a Daedalus with this type of amp. I suspect that an OTL would perform beautifully being matched with a Daedalus speaker.

Hey ... to a lesser extent, I've got amp/speaker issues too. My ARC Ref 150 amp is driving Paradigm Signature 8 v3 speakers. This is **not** a match made in heaven. The S8s have wild impedance and phase angle curves. Paradigm advises that the S8s should be driven by a high-power/high current SS amp. Oooopss. I blundered. But not that much. I've found some sonic solitude by using the 4 ohm taps (as of late), which seem to have smoothed out the rocky impedance road and improved bass response. Having a 1040 joule power supply "don't" [sic] hurt either.

In short, if everyone takes a minute to re-read the other folks' posts, I think you'll wind-up agreeing with much of what has been written.


Btw, I'm rocking with the Best of Pat Benatar CD. Having a ball!! :) :)
Quicksilver, Quicksilver, Quicksilver, Quicksilver, and Quicksilver.... any of the larger variety will do a splendid job.
Bruce, I am a moderator on another site that is unrelated to audio. In that regard they put me through some training so that I could spot posts that went beyond the pale. I don't see Unsound doing that- he attacks the argument, not the person (which is how its done). IMO debate is fine and healthy- and is what forum sites are for. In the end, the debate can help people gain education or at least viewpoint on a subject.

George is different that he attacks the person (look for the word 'stupid' in his last post) and he will often negatively engage in topics just so he can get a rise out of other posters. That is one of the definitions of trolling. (As a side note its also pretty evident that he does not know what he is talking about WRT the ZEROs.)

This site does not employ a 'Report' function so its pretty hard to alert moderators when this sort of thing is going on- they have to encounter it on their own.

Unsound- I see that you reposted some earlier comments I made and one from Duke; I don't see exactly why though. Could you elucidate?
Ralph, as I have come to better appreciate, there are very few if any perfect solutions to audio technical issues. It seems that EE/designer folks like yourself make judgments and compromises to achieve a certain balanced product that has market value within its market niche.

For that reason, I think that it is imprudent to think in absolutes. Having said that, I believe that if one is looking to invest significant sums into their rig, they can avoid obvious pitfalls and clear mismatches, for example, matching a low powered SET amp or a high'ish output impedance tube amp with a low sensitivity rock n' roll impedance curve speaker, like my Paradigm Signature 8s.

(It's only through dumb luck that my Ref 150 can do a decent job driving these beasts. Should have picked another speaker, or kept the speakers and opted for a top drawer SS amp like a Pass or Ayre.)

So, I share your view. We are adults and should be polite, albeit a little tongue-in-cheek humor from time-to-time is ok by me. :)

By the way, I thought the primary focus of your comment about using ZEROs was with respect to matching one of your OTL amps with ESLs like Martin Logans which have extremely low impedance specs at high frequencies. Quite honestly, if I loved ML ESLs, I would have some agita matching that transducer with pretty much any amp, SS or tube, unless the amp was rock solid stable and wouldn't distort driving juice into a .5 ohm load.

Btw, btw, after having read your posts again, I changed the output taps on my Ref 150 from 8 ohms to 4 ohms ... again. Although gain was clearly reduced because I was using the 4 ohm taps (about 2.5 db less than the 8 ohm taps), I think it quite possible that the amp was producing cleaner power (i.e., less distortion).

Bass is clearly more extended and tighter. No surprise there since the output impedance off the 4 ohm taps is less than the 8 ohm taps (therefore higher DF). Plus, speaker impedance in the "power zone" (say 60 Hz to 700 Hz) is for the most part 4 to 5 ohms), ergo a better impedance match for the amp where it is being called upon to deliver most of its juice. Imaging was less forward (probably because midrange/treble was less emphasized as a result of higher impedance), so I turned up the gain and imaging came back. In short the rig plays louder, but not as harsh (i.e., maybe less distortion).

Regards to all,


P.S. Back to audio business, I just bought a JVC hi-rez redbook CD of Tango music from Acoustic Sounds. I'll report back with comments. I'm trying to keep track of good hi-rez CD label. So far, +1 for MoFi.
Atmasphere, I included the quotes as per your request.
The first two from you to support my premise that I wasn't putting words in your mouth.
The ones from Duke (AKA: Audiokinesis) with re: to it being easier to steady an impedance by lowering the impedance (and ergo make for a smoother frequency response).
I'm having trouble with my old memory as to whom might have suggested that lowering the impedance could help with bass response (and ergo increase frequency response), so the search for that link might be considerably more difficult. Then again if we can extrapolate the words from a very articulate, very well respected (especially here on Audiogon) amplifier designer; that one can get greater sound pressure into a 4 Ohm load with a ss amp, then we can use that extrapolation to suggest that as frequency response is measured in dBs, one can extend bass response and therefore extend frequency response.:-)
Atmasphere, Ah ha, I found one, I'm confident there is at least one more from a different source. I'll keep scratching my head.
04-05-11: Lrsky
Soundlock makes a good point.
Jim Thiel, starting in 1988, while developing the CS5's discovered that, by using bass drivers that drop precipitously in resistance, that this had a side effect of pulling more current from the amplifier--acting 'almost' as an equalizer on the bottom/bass region.
I have not discussed this, but it seems plausible, AND if Jim said it to be true, I don't need much else to bolster this opinion.
So...with that said--an amp with lots of balls, doubling as the impedence drops more and more, as they do get into the 2 ohm region with the THIEL 3.7--should mate well with a 'Krell-like' bass performer. I don't ascribe to the Magtech amp, as I haven't heard it...yet, he's right on the mark in his assessment. THIEL's need current.
As a side note--one very hard earned lesson by Jim that year was, that virtually everyone exaggerated their current delivery on the amplifiers--very few did what the manufacturers claimed.

Good listening...

Lrsky (Threads | Answers | This Thread)
Unsound, you state above "that [if] one can get greater sound pressure into a 4 Ohm load with a ss amp, then we can use that extrapolation to suggest that as frequency response is measured in dBs, one can extend bass response and therefore extend frequency response." With respect, IMO, your statement may be a non sequitor.

Here's my thought process. A speaker's SPL is a function of its sensitivity and the amount of watts the amp is driving into the load. While it is true that a 4 ohm load will draw twice as much current as an 8 ohm load, I fail to see why that necessarily means the speaker's SPL is necessarily twice as high at 4 ohms.

Consider my speaker, the Paradigm 8s. These beasts have a impedance curve that looks like a roller coaster, ranging from a low of 4 ohms in the bass/low midrange FR range and a high of 20+ ohms at the midrange/tweeter x-over point of 2K Hz. Yet ... the S8s have a very flat FR.

How can that be, I rhetorically ask? The reason is that these speakers were designed to be driven by a low impedance/high current SS amp. The fact that impedance rises to 20+ ohms at 2K Hz, thereby resulting in the speakers drawing LESS current and power from the amp, only means that the drivers are very sensitive at that frequency. Otherwise, the speaker's measured FR would be grossly skewed.

Consider Maggies. I recall reading that the 1.7s have a flat impedance function of 4 ohms or thereabouts, yet are not sensitive. As a consequence, one needs a beast of a SS amp to drive these pups to decent SPLs. In fact, I also recall reading a review of my Ref 150 that mentions the reviewer hooked up my Ref 150 amp to Maggie 1.7s and found the SPL just adequate.

As far as extended FR is concerned, I surmise that has more to do with the speaker design than it's impedance spec as a function of FR. I suspect what may have a more perceived impact on low end bass response is the amp's DF and the speaker's impedance spec. As Ralph, Al and others have mentioned elsewhere, DF is a factor equal to the quotient of a speaker's impedance at a particular frequency, divided by the amp's output impedance. The output impedance of most SS amps is so low that the amp's DF is not really a relevant stat.

But, if the amp's output impedance is "low'ish," say .5 ohms, and the speaker's impedance is "only" 4 ohms, ironically the DF will only be 8. By contrast, if the speaker's impedance is 8 ohms, then the DF jumps to 16. I surmise that the doubling of the DF may (??) have the effect if making bass sound tighter and perhaps more extended sounding.

I think Ralph was probably on target when he said that if a speaker presented a flat impedance load as a function of FR, say 8 ohms or higher, and zero phase angle over the speaker's full FR bandwidth, I think pretty much any SS or tube amp would be a very happy camper.

But as far as a speaker's FR being flat, extended or whatever, I think that has more to do with the speaker's (i) design objectives and build, (ii) impedance variations, (iii) phase angle stats, and (iv) SPL sensitivity. Of course, also critical is whether the designer intended that the speaker be driven by a SS or tube amp.

Really sorry for the long post. I hope it's cogent and the reasoning linear.

I'm sure I mixed and matched concepts, but hopefully our tech members will correct my meandering musings.


Bruce, thank you for your thoughtful response. It's late for me now, I'll try to find time in the near future for a more deserving answer. In the mean time, you might want to reread the chronology of the posts above. I think you'll understand why I ended that post to Atmasphere with a :-).
Unsound, I don't see the comments you found doing anything but supporting my position, and also this:

The bit about Jim Theil using drivers in parallel to get more current out of the amp at low frequencies is a classic Voltage Paradigm move. The problem is it also increases the distortion of the amplifier.

As the other quotes you found also state (paraphrasing) - if sound **quality** is your goal then there is no argument for 4 ohms. If sound **pressure** is the goal then there is a weak argument for 4 ohms if you have a solid state amplifier that supports that operation.

Now in the case of Jim Theil, by using two woofers in parallel, and assuming an amplifier that can produce constant voltage into most loads, the simple result will be that it makes twice as much power into the woofer array than it would if there was only one woofer. Its also likely that the woofers chosen may well be 3 db less efficient than the midrange and tweeter, if by any chance the latter are 8 ohms.

Now in the case of a Martin Logan ESL panel, the panel impedance is not the result of the behavior of a driver in a box. It is the result of a capacitor, whose range of impedance is set by a matching transformer. As a result, its not to your advantage to see an increase in power at low impedances- the panel is as efficient at 10KHz as it is at 1KHz, even though the 10KHz impedance is much lower.

It is for this reason that it is perfectly reasonable for one to use a set of ZEROs on the speaker, even though there is a matching transformer in the speaker, and perhaps another one in the tube amplifier employed. IOW, the 4 ohm tap on many tube amplifiers may not be enough to allow the amp to deal with the 0.5 ohm impedance at 20KHz that is common with many ML ESLs. Heck, a lot of transistor amps have trouble with that too- especially if a speaker cable is being used between the amp and speaker.
Atmasphere, My disagreement was and continues to be with your earlier post(s):
"Now it is a simple fact that there is no good argument for lower impedance (4 Ohms or less) in high end audio; that is to say if **sound quality** is your goal."
^^ OK. Its my contention that reducing distortion in the reproduction chain leads to better fidelity/better sound, especially if the types of distortion we are reducing are the types to which the ear is particularly sensitive.

In this regard I favor sound quality over sound pressure (volume); I think you will find that most audiophiles do.

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. If you think the distortion involved is negligible, its not, it usually is of the types that the ear cares more about.

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.

Here is the text of some communications that Paul Speltz (designer of the ZERO) has received from a well-known solid stage amplifier designer:

Hi Paul -

I hope you had a nice weekend out in the woods - it's cold out there!
I'm still enjoying the autoformers very much, and they are continuing
to improve as they break-in. I wanted to comment on why I finally
decided to try them (and wish I had a long time ago!). In the past, I
had always thought of autoformers as a "speaker tweak" or a kind of
crutch for amplifiers that couldn't handle difficult loads. I figured
that my amps could drive anything, so why worry about adding extra
boxes that I didn't need. Over the past several years, though, I have
been working more and more with line-level coupling transformers (part
of my new VRE-1 preamp design) and I have seen some evidence that
suggested to me that something in the nature of the load with the
transformers made the source driving circuits "happy," to use the
scientific term ;-) Thus I came to be interested in the autoformers as
a possible *amplifier tweak.* (I guess maybe you see them from the
speaker's point of view, while I tend to see things from the amp's
perspective.) Whatever the reason, they certainly work well, and I do
feel that the amp is "happier" with the conjugate load. Maybe it's
nothing more than a more benign impedance, but I suspect there is
something more at work. I suppose it might be possible to try them
with a high-efficiency,16 Ohm speaker as a test of some sort, but I
suspect that the sound would still improve with the autoformers.
Anyway, whatever the truth of the matter is, I am a convert.

Thanks again, Paul.

Happy holidays,

Steve McCormack
SMc Audio