Tube Amp for Martin Logan Speakers

Hi Bruce the Quad are not too bad
http://www.stereophile.com/images/66Quadfig01.jpg
when you look at the ML Monolith'
http://www.martinloganowners.com/forum/showthread.php?6301-Impedance-curver-graph&p=69831&viewfull=1#post69831

Cheers George

George, not having ever used the ZEROS, I can't speak to their pros or cons. Having said that, as I mentioned in one of my posts above, I tried a couple of gizmo tweaks in the signal path in various places and was disappointed. So, I suppose based on those experiences, I would be biased (pun) against inserting **any** artifact in the signal path .... unless my back was up against the wall.

For that reason, I would shy away from using ESL speakers with wacko impedance and phase angle curves, even if ZEROS would enable my amp to drive them. At one point, I was wondering whether picking up a pair of QUAD 2805s would be worthwhile. After doing some reading about their impedance curve, I decided against it.

Hey ... there's a lot of amp ball-busting speakers out there. The impedance and phase angle specs of some "fav" dynamic speakers are killers. So I happen to concur with the parts of your last post that counsels caution when matching amps and speakers.

As I also said above, it is only through dumb luck that my ARC Ref 150 seems (??) able to do a good job with my Paradigm S8s. Talk about amp ball-busters. I think the reason the combo works is because (i) I use a self powered sub woofer to pick up some of the low end load, (ii) the S8s are spec'ed at 92 db sensitivity, (iii) the Ref 150 is rated at 150 wpc, and (iv) the Ref 150 can presumably deliver serious current because it has a beefed up capacitive power supply of 1040 joules.

Btw, I currently use my amp's 4 ohm output taps. Output impedance is probably on the order of .5 ohms or so. If correct, the "actual" damping factor is probably 8 or 10'ish in the S8's bass region (60 Hz to 500+ Hz) because the S8's spec'ed impedance is about 4 or 5 ohms in that frequency corridor. That is clearly better than if my amp had an output impedance of 4 ohms, in which case the DF would be about ONE (1) .... not so good.

Finally, I think there is more we agree about than not. Hopefully, we'll all read each other's comments more carefully to avoid talking past each other.

Cheers,

Bruce

I do not manufacture amps that may or may not need the Zero in circuit, so there are no ulterior motives for me to hide or protect.
I just don't like to see blanket statements like the Zero will improve all amplifiers regardless of topology.
They have their place in that they make an amp that has trouble to drive certain loads with relative ease, able to do so.
But it is not the definitive answer, it is a bandaid fix, changing the amp/s or speakers is the way to go in these cases.

Here is another point made from Dick Osher's review of the Zero Autoformer that was conveniently left out of the link to the excerpt of the review.

"T-Rex 300B SET, a DIY design project in the works (still unpublished) using Plitron output transformers with only 8-ohm taps, and the Lowther DX4 BassZilla - a 97dB.
At his point, it became clear that although bass lines still benefited from the ZERO, overall the T-Rex - BassZilla interface sounded better with the ZERO out of the way."
"Small, but noticeable errors of commission crept in. Soundstage transparency diminished, which reduced the music's intimacy. Microdynamics now sounded slightly over damped, releasing some of the music's tension. The midrange, which for me paints a window onto the music's soul, became slightly cloudier. On balance, I would rather give up 20% of bass definition for a 10% increase in midrange clarity.":

As you can read the 300B set amp (and others eg OTL's) not known for good drive current, was improved in the bass area with the Zero, but the midrange diminished by 10%
The same 10% detriment will happen to the midrange using a Zero with a good solid state amp or powerful tube amp that have no problem in delivering good bass without the Zero.
The word Dick Olsher used "cloudy" in reference to the midrange is also what I heard in my system with the Zero's attached to a good SS amp that could drive the speakers with no problems, and as well as the bass tightness and drive diminished just as much with it in.

Cheers George

This is for Ralph, since I'm quoting him. But any others are welcome to jump on it as well.

"I am not stating that 4 ohm speakers are bad speakers. I am stating that any amplifier driving them will sound harsher and less detailed as opposed to the same amplifier driving the same speaker that was 8 ohms, were all other matters to be equal."

I admit my knowledge of electronics is very limited, but this raises a question for me. Is the singular impedance rating of any speaker worthwhile or even all that important? Or is a better question what is the impedance plot across a speaker's response range?

I ask this because for many years I owned Duntech speakers which were rated at 4 ohms. However, reviewing Duntech's impedance plot, it dipped close to 2.5 ohms at two points, the most troublesome being between 60 and 80 Hz as I recall. Considering the power called for at that frequency range and the dip below 3 ohms, well, not ever amp rated to drive a 4 ohm load got off easy!

So my sense is to consider the full impedance curve, not just a static number. Maybe that is where "all other matters" are not equal.

There are many, many speaker cables to choose from. I'm confident that one would find many (if not most) will work just fine with a 4 Ohm load speaker.

03-27-14: Atmasphere: do so despite George's remonstrations

Are you kidding, far from pleading with you Ralph.

I agree that an Autoformer is a great (pseudo) bandaid fix for whatever amp that cannot drive a speaker that is not a good match, because of it's inability to deliver current/wattage or is working out of it's SOA (safe operating area) A FAR BETTER FIX IS TO CHANGE THE AMP/S OR SPEAKERS!

You state that even a good solid state amp will measure less distortion on it's output from using a Zero Autoformer into a 4ohm load compared to 8ohm.

Yes I agree that with the Autoformer even a good solid state amp will measure slightly less distortion at it's output terminals at 4ohms (this is not to say it's out of it's SOA)
But it's what happens after the Autoformer (things like phase shifts, damping factor etc) that is far more detrimental to the sound than the slight increase in distortion before it without the Autoformer.

EG: What one would basically do to a good amp say like a Pass Labs, Krell, Gryphone or similar amp by sticking an Autoformer on it, is to turn it into the solid state series MacIntosh's that also use a type of Autoformer on their outputs, but without the benifits of using them within the amps feedback loop, to keep the (damping factor, phase shifts, etc) in check.

Cheers George

YEs, but realize that tube amps in general will distort even more than SS amps into 4 ohms, so if 4 ohms is part of teh puzzle, the answer is clear.

Any good amp, SS or otherwise can drive an easy load easier.

SO you have to look at all the pieces of each puzzle together in the right way , not take one piece from one puzzle and try to insert it into the the other and then blame it for not working.

Likewise, there is always good, better and best in any case/scenario. Its important to understand impedance and phase related issues in order to assemble the right pieces. Then you can assess system/puzzle A versus B however one likes, but better to look at the overall results than the relative deficiencies or strengths of any one element of design.

BTW, as I read it; George didn't call you stupid, he called one of your suggestions stupid, and that was after you called him a "troll", which was after he posted a link where he recommend your product. This line of posting is somewhat out of character for you.

Hi Unsound, yes it is, and one should consider that I do refrain from that sort of thing as much as I can. Recommending the ZERO is something I have done a lot, and not just for our amps and I will continue to do so despite George's remonstrations. This is for no other reason than the ZERO really does work.

One other thing- to clarify, I am not stating that 4 ohm speakers are bad speakers. I am stating that any amplifier driving them will sound harsher and less detailed as opposed to the same amplifier driving the same speaker that was 8 ohms, were all other matters to be equal. Put another way, a simple method of making a speaker seem more transparent and easier to listen to is to make it be higher impedance.

This might be all about how important it is to an audiophile to have increased transparency/detail, coupled with a smoother presentation. I like those things myself.

Something I have not mentioned yet is the effect of the speaker cable on 4 ohm speakers- but it should be obvious that they are far more critical for a 4 ohm speaker than the cables are for 8 or 16 ohms. Damping factor of amplifiers is normally stated with respect to an 8 ohm load; that number is initially cut in half with a 4 ohm speaker. Add to that the seemingly low DC resistance of the speaker cable and the damping factor of the amplifier is reduced considerably more that one might intuit. RCA published a nomograph that showed this relationship several decades ago.

Well stated Mapman! :)

I think the EPDR link I provided supports Ralph's comments that low impedance speakers may have an even lower EPDR rating than what is nominally reported or measured. Even more important is that speakers presenting low EPDR factors significantly contract an amp's so-called SOA.

I am not saying that 4 ohm speakers are not good performers. Just that a nominal 4 ohm load in the bass region may really squeeze the amp and possibly result in a referral to the SPCA. At a minimum, a less than optimal amp/speaker match may, as the article explains, result in distortion. So, I happen to think Ralph's comments make sense for the reasons set forth in the attached article.

Bruce

P.S. The SPCA is the Society for the Prevention of Cruelty to Amplifers.

Clipping is always the devil to avoid when chosing an amp for speakers. Effects of clipping start as subtle and increase to major. Whatever the speakers, be sure to chose an amp that is well beyond being up to the task. Most speaker vendors quote minimum or recommended amp power rating that are suitable to get decent results for most, but not suited to get the best results possible, which is what audiophiles seek. Result is many underpowered systems out there over the years and that is valid fuel for the argument towards speakers that present an easy load.

High efficiency/easy load speakers are a viable solution to the problem, but no the only one, especially these days. Amp technology has progressed and offers major improvement in efficiency these days as well. Monster heavy and big power amps ala traditional Krell, etc. are no longer the only robust option. Class D amps are lightweight, small, efficient and offer more power for the $ than ever.

SO do not disregard modern innovations in amplifier technology when assessing options. THere are more good and affordable ones out there than ever, especially when TCO is considered.

Also, use of powered subs to offload the heavy work in the bass is another very practical tool to choose. WHen powered subs are used (most use Class D amps to very good effect here) a lot of the issues with matching speakers to amps that exist otherwise tend to go away in that the main amp is asked to do much less to drive the speakers optimally than otherwise.

Also when playing vinyl, always make sure rumble and subsonic noise in herent in many phono setups is managed properly and under control. Otherwise, most of the amps headroom will be used to produce noise. High efficiency/easy load speakers might be a band aid in this case, but not the solution.

Folks, some may find the Stereophile article about "EPDR" quite interesting at this link:

http://www.stereophile.com/reference/707heavy/index.html

I think one important take-a-way is that speaker impedance ratings, by themselves, do not take into account the full picture of speaker's load difficulty. Other factors include a speaker's phase angle characteristics. Take a look at the Final 600i ESL. Talk about an amp ball-breaker.

But perhaps even more relevant to this thread and Ralph's comments is that most amps have a real world "SOA" re power dissipation that is a lot less than one might expect. As defined in the article, the acronym SOA stands for Safe Operating Area. Please note that an amp's SOA power dissipation contracts considerably as impedance decreases and negative phase angles increase in magnitude.

I'll let our techy members comment further, but suffice to say that low impedance loads can cause an amp to operate at or outside its SOA, thereby causing distortion. I surmise that if a particular brand amp's SOA is small when driving a low impedance load, the answer is to buy a more powerful amp that has a less restrictive SOA or try ZEROs.

Final two points. First, the article speaks about SS amps. Nonetheless, I surmise that similar principles apply to tube amps. I understand the SS amps hard clip while tube amps generally soft clip. But I think common to both types of amp is that distortion dramtically increases once the amp exceeds its SOA. The second point is that when Ralph uses the term "happy amp" he no doubt is referring to an amp that is operating within its SOA.

My heads hurts because I have no idea what I just wrote.

Goodnight.

"You can see in the specs of any amplifier (solid
state, class D or tube) that the distortion is indeed higher
driving a lower impedance load. "

That is true, but still all relative, and 4 ohms does not
mean many amps stop performing well.

Needless to say, the amp has to be up to the task. Most
good quality SS amps these days are quite capable of
performing well into 4 ohms these days it seems. Lower
than that becomes more of an issue perhaps, but better to
listen and determine for ones self the whole story rather
than focus on any one technical scenario. 4 ohm loads are
quite common these days and for good design reasons, not by
error or ommission. There are many valid ways to achieve
excellent results.

Tube amps are a different beast that work best in different
scenarios and subject to their own unique distortion
characteristics, so comparing SS and tube amp distortions is
not apples/apples and of limite.d value IMHO

Atmasphere, on the surface, I don't think anyone would argue that reducing distortion would be a good thing. But we have seen when distortion reduction specifically and unto itself with disregard for the whole can cause more harm than good.
From the above; it seems that Steve McCormack's thinks that the autoformers made his amp "happier". Well, I might believe that, but that unto itself doesn't mean a whole lot when considering the whole lot.
There is apparently more to low impedance than just "sound pressure" (I'm not putting words in your mouth, am I?). For many years in the past, and very much in the present, and I'll hazard a guess, that for many years into the foreseeable future there will be speakers with low impedances with high end aspirations. I would caution those considering acquiring loudspeakers not to dismiss loudspeakers that have low impedances. There are many, many superior loudspeakers that might be missed out on. There are many amplifiers capable of driving them just as they come from the factory.
With all due respect, we've going back and forth on this subject for years now. Unless there is a drastic change in the audio landscape; as long as you keep making the assertions:
"Now its a simple fact, that there is no good argument for lower impedance (4 ohms or less) loudspeakers in high end audio; that is to say if sound **quality** is your goal."
I will probably object. In an effort to save time and bandwidth, perhaps we can come to some sort of gentleman's agreement on how to deal with this in the future?
BTW, as I read it; George didn't call you stupid, he called one of your suggestions stupid, and that was after you called him a "troll", which was after he posted a link where he recommend your product. This line of posting is somewhat out of character for you. You're better than that. But, hey, we're all human.
Best Regards,
Unsound.

03-26-14: Atmasphere
This can be so significant that the use of an autoformer to raise the load impedance to an otherwise very capable solid state amplifier can result in improved sound. Were this not the case, the insertion of the autoformer would have adverse effects.

OMG, it does, if the listener had ears. I've tried them on a very capable ss amp, and the sound took a bad turn for the worse.

Quotes: from the Dick Olsher review that was convienently left out of the excerpts of the reveiw of the link you provided on the Zero website, read between the lines, we all know that reviewers don't like to rock the boat too much.

"It is not a panacea, and as you can see from my experience, it does not always pan out. However, if you're the proud owner of an OTL or a low-power tube amplifier and presently driving a 4-ohm loudspeaker load, you owe it to yourself to give the ZERO a try."

Cheers George

^^ 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

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."

Unsound, I don't see the comments you found doing anything but supporting my position, and also this:

http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

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.

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, 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.

Regards,

Bruce

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...

Larry
Lrsky (Threads | Answers | This Thread)

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.:-)

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,

Bruce

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.

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?

Quicksilver, Quicksilver, Quicksilver, Quicksilver, and Quicksilver.... any of the larger variety will do a splendid job.

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.

IMHO.

Btw, I'm rocking with the Best of Pat Benatar CD. Having a ball!! :) :)

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
permits.

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.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1304533364&openfrom&23&4#23

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

"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.

^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)


http://forum.audiogon.com/cgi-bin/fr.pl?
cspkr&1356668050&openusid&zzAtmasphere&4&5#Atmasphere

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.

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.

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.

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?

I'd have the $18000 gold bar drawn into wire and sent it to JD (Jadem) to make me a full cable loom:)

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

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

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.

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.

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.

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'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.

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.

Hi,
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.

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

Hi,

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.

^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 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:

http://www.zeroimpedance.com/zeroimpedance_002.htm

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.

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.

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

Once again I disagree with Atmasphere's oft-repeated assertion.

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?