Richard Clark $10,000 Amplifier Challenge - Why Couldn't Anyone Pass this Test??


Any guesses? 
seanheis1
Everyone knows that well built solid state amplifiers designed to stringent specifications and tolerances are going to sound very much alike at low volumes.

It would be a huge surprise if that weren’t true - it would mean that all those measurements and engineering principles and the consistent improvement in amplifier performance are completely wacky and wrong.

It is when you stress a SS amplifier that differences may be audible - at higher SPL and with challenging loads or with dirty power or when driven close to clipping and where distortion rises rapidly.

That said, there will be very small differences even at low volumes but these will extremely difficult to discern reliably with most music sources unless using very specific test signals.

So no surprise to me.
http://tom-morrow-land.com/tests/ampchall/
Why couldn’t they pass the test? The same reason why a panel of experts cannot tell the difference between a Stradavarius and any other well made reasonably good sounding violin. Did anyone ever pass one of The Amazing Randi's $1 Million challenges? I don't think so.

Because all properly designed and built amplifiers not in clipping sound exactly the same, of course ;-). But seriously, shadorne's assertation that "well built amplifiers....." can be proven to be untrue by hooking up a low-powered class-A amplifier (a Pass Labs or First Watt would be nice) to, for instance, the original QUAD ESL, a very transparent loudspeaker. My Bedini 25/25 driving my QUADs sounds dissimilar from my two high-powered class-A/B amps doing the same. As Nelson Pass suggests, it is an amp's first couple of watts that matter the most!
Post removed 
I have to say that amps aren't where the SQ impact really lies in an audio system.

But I've never seen what "high quality home type loudspeakers" anyone has used, or what source material.

You guys can always put up your $200 and see how you do.
The idea that you can’t tell the difference between a violin or viola you know very well and others is nonsense.

Not only do they have a specific character, over time the fibers and resins break down depending on how they are played, which musician’s can tell, while listening or especially while playing. The elasticity of the entire piece changes over time. Ask any violin maker.

Now, can I hear a recording and say "Aha, an early Stradivarious!" NO, i really can’t, but I am sure i could become accustomed to a particular instrument and hear it vs. others.

Best,


E
So my previous remark was about violins. Any half hispanic, half asian lady, mostly single, concert violinist between 35 and 45 years old who would like to come to my home and prove I can’t tell the difference in which violin she’s playing, please let me know so I can arrange a time.

Now, about amps.

I can make speakers more "discerning" of amplifiers than others. I learned this trick from a famous speaker maker’s crossover. Lower the impedance and make it particularly reactive in the mid bass and voila, now you can tell the difference between several amplifiers which in a "Lesser" speaker you could not.

This is a reason why I strive to make my speakers easy to drive. Easy to drive means they will sound great across a variety of amplifiers and electronics. I think this is part of what is going on. There are a lot of good modern amps which sound really similar. We live at a time when many amps sound free of glare and harshness or grain, smooth, extended and potent with easy to drive speakers, but not all speakers are easy to drive. :)

For those who wish to be dominated by their speakers however, I can point you at some famous brands. :)


Best,


E
Also want to say, we are lucky to be alive right now. There are some wonderful Women and Men making violins, violas and cello’s these days for relatively paltry sums compared to buying a Strad.

Anyone who gets a chance to listen to an accomplished violinist should also be grateful for a chance to hear such remarkable craftsmanship.

E
@bdp24   

Not surprised by your finding as Quad ESL can be an extremely tough load. Differences in amplifier damping (output impedance) would be quite audible. This only proves one of the major design issues with Quad.
This is a reason why I strive to make my speakers easy to drive. Easy to drive means they will sound great across a variety of amplifiers and electronics.
+1

Not surprised by your finding as Quad ESL can be an extremely tough load. Differences in amplifier damping (output impedance) would be quite audible. This only proves one of the major design issues with Quad.
This passage is false.

The 'original Quad' (as bdp24 put it) is an easy load to drive. Differences in damping between amps is one of the few things that **isn't** audible on the speaker, owing to the fact that in the bass range the impedance is rather high. This reduces the difference heard between an amp with say 10:1 damping factor as opposed to one with 100:1.

OTLs are traditionally thought to not be able to drive 'tough loads' but OTLs can drive the Quads with ease. The real issue here is that the Quad is pretty transparent and does not need a lot of power, so its that 'first watt' that becomes so vitally important. Many traditional solid state designs are not so good at that first watt. Put one on a 'scope sometime and look at how they behave. Usually they have much higher distortion in the first watt than they do at higher powers until they approach clipping.
Post removed 
To actual musicians, the "feel" of the instrument is what counts, and Strads (not all of course) seem to have a feel and tone that people who play them really like, thus they might play better using them. Nobody disputes that fact really, and since there are a limited amount of zillion dollar Old Master built instruments out there, most good musicians can’t get near one…so, of course, they use other things and sound fine. Note that among Strads and other old and great violins the utility is often tweaked (i.e. repairs are made) that would be blasphemy among "vintage" guitar players (something I actually know something about as I am personally vintage). I saw a 50s Stratocaster advertised at Mandolin Brothers that didn’t actually work because to make it work you’d have to replace an original part (an original tone or volume pot or something), and that would make it less valuable!…love that…also, since Brazillian rosewood isn’t legal now (new stuff anyway), Martin Guitars is taking guitars from the 60s and 70s (a less than "special" era) apart for their rosewood, and making new and expensive high end guitars out of the backs and sides…clever bastards. The good news is there are thousands of great instrument makers doing fabulous work these days, so great instruments are available.
@atmasphere

Wrote this false and misleading statement (<-----  a paraphrase of how atma has posted):

The ’original Quad’ (as bdp24 put it) is an easy load to drive. Differences in damping between amps is one of the few things that **isn’t** audible on the speaker, owing to the fact that in the bass range the impedance is rather high. This reduces the difference heard between an amp with say 10:1 damping factor as opposed to one with 100:1.

Rather than argue with someone desperate to be an authority, I submit this link:

http://www.quadesl.com/quad_main.html

Best,

E
IMO it is a somewhat misleading oversimplification to categorize the ESL57 as being either an easy load or a difficult load.

It is a difficult load in the sense that its impedance descends to low values in the upper treble region, due to the capacitive nature of the impedance. Although even in that region its impedance is not nearly as low as the sub-1 ohm impedances of some other electrostatics, such as many of the Martin-Logan designs.

However, that difficulty is of course mitigated by the fact that most music contains relatively little energy in the top octave, where the impedance is particularly low.

It is an easy load in the sense that damping factor is a non-issue **with respect to bass control,** as Atmasphere indicated, because of its high impedance in the lower parts of the spectrum.

However, it will be a load that is **revealing** of amplifier differences, not only because of its transparency and musical resolution, but because differences in damping factor among different tube amps, and also between tube amps and solid state amps, will have tonal consequences.

Damping factor is inversely proportional to an amplifier's effective output impedance.  (I add the word "effective" to indicate that I am referring to output impedance taking into account the effects of whatever feedback may be present). The interaction of the amp's effective output impedance and the speaker's wide variations of impedance over the frequency range will certainly have tonal consequences, especially among different tube amps, and between tube amps and solid state amps. Less so among different solid state amps, since their effective output impedance is near zero in most cases.

In any event, the bottom line with respect to the tube-friendliness or lack thereof of the ESL57 is perhaps indicated by the fact that it was designed before solid state amps existed.

Regards,
-- Al
 
@erik_squires   

+1 the link you gave states this about Quad:

"The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases. This makes the Quad ESL a bad choice for single ended tube (SET) amplifiers."
@almarg    

+1 that is what I stated I even clarified that damping equates to  "(output impedance)" 
" They need about 15 Watts of the best amplification you can get your hands on."

" The Quads will play up to about 100 dB, which is much louder than I play music even when playing loudly. "

" The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases. This makes the Quad ESL a bad choice for single ended tube (SET) amplifiers. "

I think I can figure out why this guy isn't an authority, desperate or not.
All ESL panels I know of follow this descending impedance curve, which is a problem for a lot of amplifiers since most amplifier’s have rising impedance at the upper end of the frequency spectrum, resulting in an overall significant net loss of output.

This is in addition to current limiting, which thanks to music being bass heavy, is less of a concern.

Tube amplifiers rarely have the low output impedance (anywhere) that solid state amps do so they start at a disadvantage.

However this is all basic electrical / and voltage dividing theorems. The final choices about matching any given amp to any given speaker has to include the speaker’s acoustic output and room.

Given the impedance curves of the amps and speakers you can predict reliably that amp X’s electrical output will drop 6 dB at 20 kHz with a given speaker, but I can’t tell you if you’ll like it. :)

Best,


E
So this brings me full circle. I've seen speakers that are hard to drive at the top end, at the bottom and all across the spectrum.

The ESL speakers come by their low impedance and difficulties as do the full-range planar-magnetics (Apogee) via legitimate reasons. That is, the speaker technology itself poses challenges which the designers accept in exchange for other benefits. ESL's are essentially giant capacitors, no way to get around that.  The sacrifice is made to submit the amplifiers to brutal loads in exchange for having a large single driver driven across it's surface (how well ESL's actually do this is arguable, but not for here).

I think that with the worst of these panels, a lot of OK amps are going to perform quite a bit differently, which with "nice" speakers could perform nearly identically.

And  as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers.  When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way.

But this discernment does not make either the amplifier or the speaker more musical. It's just more demanding.

Best,


E


And as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers. When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way.

But this discernment does not make either the amplifier or the speaker more musical. It’s just more demanding.
Yes, I am very much in agreement, Erik. As I and some others (including Shadorne) have said in other threads here, the musical resolution of a component or system, and its ability to resolve differences between components, cables, or tweaks, are two different things. And generally speaking the correlation between the two, while certainly not zero, will be a loose one.

My perception has been that many audiophiles fail to recognize that point, as evidenced by how quick some are to allege lack of resolution (referring to musical resolution) as being the reason others may not hear differences when performing comparisons between various hardware.

Regards,
-- Al

They need about 15 Watts of the best amplification
The above quote is taken from the link Erik provided.

I've serviced the 15-watt tube amps that Quad made to go with the '57s; in a nutshell driving a 'difficult load' is something they can't/don't do. But they drive the Quads just fine.

When 15 watts is all that's needed, its not a hard load and no mistake :)

As Erik points out, the impedance curve is very typical of an ESL.

I suspect that what Shadorne calls 'difficult' (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can't make as much power into the relatively high impedance that the Quad presents at low frequencies. So you might need a 60-watt solid state amp to make the sound pressure on the Quad that a 15-watt tube amp can. But it will still play it, and if one puts one's hand on the heatsinks of said solid state amp, it will be found that the heatsinks won't get all that warm, despite hours of operation (unless the amp is class A)!

IOW, the solid state amp isn't working that hard. Why? Its not a difficult load; the amp is never asked to make anywhere near the power of which its capable. The 'difficulty' might be that the Quad will easily reveal the shortcomings of any amp which is asked to play it; so to get the best out of this speaker, you need a good amp. But that amp does not need a lot of current capability, which is traditionally associated with driving 'difficult' loads. We have lots of customers with Quads and they usually use our smaller amps. Folks, 'small OTL' and 'the ability to drive difficult loads' are two concepts not normally found together :)

The simple fact is, this speaker can be driven by a variety of amps (including SETs) that are not known for being able to drive 'difficult' loads. I would not use an SET in this case simply because I don't know of 15-watt SETs  that can make the bandwidth that the Quads can, but if you have one, it will work fine.

This is an excellent example of how not all amps are the solution for all speakers!
The Quads have issues. First of all they need to be on stands, I had the Arcici stands. Secondly, they need to have their metal grills removed. The grills suffocate the speakers. The Mylar dust covers should also be removed. If you’re nervous about dust in the room get an air purifier or two. Finally, the Quads benefit from better power cords. All of these actions result in tremendous dynamics and bass performance.

Old news - Peter Aczel was saying this in the 80's.  Not worth talking about IMO.  I've owned $25k amp/preamp combos and liked them and I've also used a $200 Onkyo reciever while an amp was being repaired and I liked that too.  Personally, I think the more expensive high-end stuff sounded better and that's what I choose to own and listen to and I couldn't give two shites about what someone else thinks.  And respectfully, either should you .  
I cannot totally Agree,  I have been running pure class A Pass Labs 
And most certainly better then the majority of Class An amps 
Even my brothers Pass 250.8 is far superior yhen most evrn st low volumes 
We compared  a bunch of Audiophile friends gear over 6 months.
The average AB amp could not compete in resolution .
One big reason is the very High bias in class A  for almost the first 20 watts 
Which is a lot with a 90db dpeaker..   The Valvet mono blocks are around 100 wpc
Into 4 ohms pure class A and incredibly detailed at  Low volume .
Vitus, is another HIGH POWER great sounding amp even met low late night 
Low level, as well as Gryphon Diablo ?this and the Vitus,integrated are the 2 best 
Integrated amps I have ever heard at all levels and passed the acid test .
I owned a Aufio store until 06 in Europe the new models are even Better.
If you are willing to spend these are exceptions to the rule.
With respect to the talk on old and new violins, I'm surprised no one has mentioned these two studies:

Is A Stradivarius Violin Easier To Hear? Science Says Nope

Double-Blind Violin Test: Can You Pick The Strad?
yage
With respect to the talk on old and new violins, I’m surprised no one has mentioned these two studies:

Is A Stradivarius Violin Easier To Hear? Science Says Nope

Double-Blind Violin Test: Can You Pick The Strad?

>>>>Actually, your humble scribe mentioned those inconclusive "scientific" tests by trained professionals with Stradivarius vs X brand 4 days ago on this very thread. Hel-loo!

@geoffkait  - Ah... didn't see any links, so wasn't sure that's what you were posting about.

I think the conclusions were pretty clear, though: new violins sound quite good.
Everyone knows that the difference between a violin and a viola is that a viola holds more beer.

yage
@geoffkait - Ah... didn’t see any links, so wasn’t sure that’s what you were posting about.

I think the conclusions were pretty clear, though: new violins sound quite good.

>>>>>Yes, either that or trained musicians are relatively tone deaf or whatever, which I actually prefer.

I suspect that what Shadorne calls ’difficult’ (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can’t make as much power into the relatively high impedance that the Quad presents at low frequencies.

oh sure. Uh huh.

If this had any basis in reality, at all, speaker testing would be based on power vs. frequency. It isn't. It is input voltage vs. frequency.

Best,

E
Theory is too difficult to do in these forums, especially without graphs, but let’s talk some real world effects.

SoundStage Magazine online has a review for the Atma-Sphere MA-1 Mk II.2 mono-blocks:

http://www.soundstage.com/revequip/atmasphere_ma1ii2.htm

with an excellent set of measurements which to illustrate what the output impedance problem is with typical tube amps and how much it is.

The very first graph shows how the amp interacts with the complicated impedance of real world speakers. See the green line? That is what the electrical output looks like when driving a simulated speaker load. The frequency response can vary around +-3 dB (a bad thing) when driving an NHT:

http://www.soundstage.com/measurements/atmasphere_ma1_mkii2/

I think this is quite typical behavior for tube amps. Most solid state speakers would be quite flat, debunking the idea that solid state amps have a harder time, ever.

Despite the impression Atma tries to give, almost all speakers are designed as voltage-dependent devices. I know, I make them. :) That is, the prime quality we seek is to have a smooth and controlled frequency response for a given input VOLTAGE, not power. The power is going to vary up and down based on the crossover, drivers and even cabinet.

We like to assume the amps driving our speakers is what is called an "ideal voltage source." where current (and power) output will vary based on the speaker, but the output voltage is purely a function of the input signal. This gets harder to do with high output impedance amps, or low impedance speakers.

If your amp’s impedance is high enough, it will become an ideal "current source" where the output current has nothing to do with the load, and therefore the voltage at the speaker will vary wildly with the speker’s impedance. Atma-sphere has a unique perspective on this issue, and seems to constantly be suggesting a current source is ideal. He stands very much alone in this area.

That being said, the question of sound quality and amp/speaker matching is purely subjective, and you should listen for yourself. I'm pretty sure my favorite tube amps of all time, the CJ Premiere 8s were quite high in output impedance, but I'm not going to try to sell new physics to convince anyone to buy them.

Best,


E
The test is CD based. That might be why.
Bingo!

If this had any basis in reality, at all, speaker testing would be based on power vs. frequency. It isn’t. It is input voltage vs. frequency.

Hmm. So you’re saying that a solid state amp can make as much power into a 30 ohm load as it can an 8 ohm load? And that with an ESL, the impedance curve is also a graph of its efficiency? I think we both know that neither is the case.
SoundStage Magazine online has a review for the Atma-Sphere MA-1 Mk II.2 mono-blocks:

http://www.soundstage.com/revequip/atmasphere_ma1ii2.htm

with an excellent set of measurements which to illustrate what the output impedance problem is with typical tube amps and how much it is.

The very first graph shows how the amp interacts with the complicated impedance of real world speakers. See the green line? That is what the electrical output looks like when driving a simulated speaker load. The frequency response can vary around +-3 dB (a bad thing) when driving an NHT:

http://www.soundstage.com/measurements/atmasphere_ma1_mkii2/

I think this is quite typical behavior for tube amps. Most solid state speakers would be quite flat, debunking the idea that solid state amps have a harder time, ever.

The conclusion here is false; starting with ’with an excellent...’. The reason is that the MA-1 is a zero feedback device and is not a ’typical’ tube amp! If it had enough feedback (about 20db), it would behave as a voltage source and the test as shown would have measured flat. Also, this does not debunk the idea that a solid state amp will have troubles driving higher impedances.

IOW, this is typical behavior of a **zero feedback** tube amp and not that of one employing feedback.

So one has to ask why we would make an amplifier that has no feedback with resulting (apparent) FR errors, and the answer is that feedback adds higher ordered harmonic content that is easily detected by the human ear. We get low distortion without feedback (assuming that the test equipment does not ground one of the speaker terminals which can result in a bogus test) so then we are simply looking to find a speaker with which the amp will have flat response.

Dr. Herbert Melcher, a neuro-scientist, has shown that the brain has a variety of tipping points. One of them appears to be that the ear/brain system will favor distortions interpreted as tonality over actual FR errors. So our approach is that if we can minimize the tonalities generated by the amp due to distortions, it can often appear to be more neutral than amps that measure much flatter on a given speaker on the bench.


Despite the impression Atma tries to give, almost all speakers are designed as voltage-dependent devices. I know, I make them. :) That is, the prime quality we seek is to have a smooth and controlled frequency response for a given input VOLTAGE, not power. The power is going to vary up and down based on the crossover, drivers and even cabinet.

We don’t try to give this impression! Erik (@erik_squires what is the brand of speaker you make?) is correct otherwise; most speakers are Voltage Paradigm devices. But not **all**; some are based on the prior Power Paradigm, as are zero feedback tube amplifiers (see link at the end of this post). If you’ve ever seen an older speaker with midrange and tweeter level controls, the reason they are there is not to adjust the speaker to the room but instead to match to the voltage response of the amplifier. These controls are not seen on Voltage Paradigm loudspeakers.

Long ago we discovered that our amps sounded much better without feedback (smoother, more detailed, wider and deeper soundstage). It took a while to find out why! In the meantime though, we have always been very careful to ascertain which speakers would be a good match. This is important (at least to us), because this is the dividing line between what makes for a good hifi as opposed to what sounds like real music. That we are still around 40 years later suggests that there are good number of speakers that work with our amps.

This is not to say that a Voltage Paradigm speaker can’t sound like real music; it is saying that if that speaker won’t have flat response without an amplifier employing a lot of feedback, then that speaker will never sound like real music on account of the amp.

The **reason** is that loop negative feedback ignores a fundamental law of human hearing which is how we detect sound pressure. Rather than detecting the volume of a fundamental tone, our brains sort out sound pressure by detecting the strength of higher ordered harmonics associated with that sound (which are increased if feedback is employed, although in ’trace’ amounts, but our ears are literally tuned to detect those traces). If the harmonics are louder than they should be, then the fundamental(s) will be interpreted to be louder too. That would not be such a bad thing but the extra harmonics are also interpreted as brightness and hardness by the ear /brain system and that is why they impart the sound of a hifi instead of real music.

BTW, this is easy to prove using simple test equipment.

So we abandoned feedback and as a result the Voltage Paradigm as it has that fundamental flaw (although otherwise works great) and went back to the Power Paradigm (which was what was around prior).

We’re not the only ones; SETs, horns, ESLs and a number of other speakers (which are admittedly limited to high end audio) are also built around Power Paradigm principles; we’re not the first or only ones that have sorted out that loop feedback isn’t perfect (see the writings of Norman Crowhurst; these problems have been known for over 50 years).

The Soundstage test assumes that all amps are based on the Voltage Paradigm and the simple fact is they are not.

If your amp’s impedance is high enough, it will become an ideal "current source" where the output current has nothing to do with the load, and therefore the voltage at the speaker will vary wildly with the speker’s impedance. Atma-sphere has a unique perspective on this issue, and seems to constantly be suggesting a current source is ideal. He stands very much alone in this area.
This statement is mostly false. Why: We don’t hold this viewpoint, and Also a current source amp will have an output that in fact varies according to the load, but in an inverse way. Nelson Pass has built some amps based on this principle, but he never made any such amp for production, and I’m not aware of anyone who has. Current Source amps IOW never developed any sort of following.

Put another way, if the impedance of the amp is low, it is likely to act as a voltage source. If the output impedance is medium (a few ohms, like SETs and our amps) then the amp will act as a Power source (constant power into all impedances rather than constant voltage). If the output impedance of the amp is very high, multiples of the speaker impedance, then it will be a current source.

That being said, the question of sound quality and amp/speaker matching is purely subjective, and you should listen for yourself. I’m pretty sure my favorite tube amps of all time, the CJ Premiere 8s were quite high in output impedance, but I’m not going to try to sell new physics to convince anyone to buy them.
Listening of course is what this is all about :)

The cj has a fairly low output impedance owing to the loop feedback employed and behaves as a voltage source. It has a classic tube sound as you might encounter with any excellent hifi.

For more on the Voltage and Power Paradigms see
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
@atmasphere

I am saying your entire argument is bunk, because the ideal audio amplifier is a voltage source, not a current source. In essence you are also arguing for amplifiers of TINY damping factor being ideal. Not supported by anyone but you.  In fact, the amplifier I quoted, has a damping factor of around 0.8.  That's about 400x worse than even a mediocre solid state amps.

Complementing the amplifier design, speakers are measured by the output vs. frequency based on constant input voltage. For your theory to be at all accurate, speakers would have to have flat power efficiency (input vs. output) and ....they don't! The power efficiency of almost all multi-way speakers varies tremendously based on frequency. The LAST thing on earth you want is a constant current amplifier, unless you want your output to look like your impedance curve.

If you are right, then man, 10 Ohms is too low. You should make amps with 30 or 50 ohms at the output, you would get even more ideal current sources! << hahahahah >>

You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again.

Best,

E
Changing the subject entirely, Ralph, did they ever retire that Nobel for Patience?
Erik_Squires 5-15-2017

atmasphere:
I am saying your entire argument is bunk, because the ideal amplifier is a voltage source, not a current source.
I’ll have to disagree with you on this, Erik. The ideal amplifier is a voltage source if the speaker it is used with is designed to sound its best when driven by a voltage source. As Ralph indicated, many speakers are not designed that way. While some others (such as the Daedalus Ulysses I use) don’t particularly care about amplifier output impedance or voltage source behavior, as their own impedance is very flat. And of course many people get great results with tube amplifiers such as SETs that have output impedances similar to the output impedances of Ralph’s designs (e.g., 2 to 4 ohms or so for most models).

Also, as Ralph indicated the output impedances of his designs are not nearly high enough for them to be considered to be current sources.

Finally, as I said earlier in the thread, "the bottom line with respect to the tube-friendliness or lack thereof of the ESL57 is perhaps indicated by the fact that it was designed before solid state amps existed." Although admittedly my understanding is that many of the tube amps of that era did incorporate significant amounts of feedback, which in the case of those amplifiers brought them somewhat closer to behaving as voltage sources than many high quality modern tube designs.

Best regards,
-- Al

Hi Al,

There are flat impedance speakers out there, which is often accomplished with additional impedance normalizing circuits in the crossover. Certainly a niche.

In these cases it is rightfully argued that the output impedance of amplifiers will have negligible effect on the frequency response.

If this was Atma’s argument I would leave it alone. His repeated disinformation that the high output impedance is BETTER because it has constant power output regardless of impedance is nonsense. In no measurable case is it ever better. The measurements by SoundState and Stereophile are consistent. With "normal" speakers high impedance causes significant deviation from ideal.

Of course, buy what you like.

Best,


E
What Al said, plus

You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again.

What is it that you're saying here? That I build good products, but - ? they aren't real or something? I'm sensing a contradiction here.

IMO you've been misreading what I've been writing.

I have qualms about **feedback**, not output impedance, as long as the low output impedance does not come with added higher ordered harmonics. And I can back my qualms up easily enough without going into the weeds. If you are not familiar with Norman Crowhurst, he is a well-known authority in the field of amplifier design. His books are likely a bit rare but the important ones are a free download from Pete Millet's site:
http://www.tubebooks.org/technical_books_online.htm

In fact I would love it if I could make the output impedance of our amps lower. The problem I have with solid state is that many semiconductors have a non-linear aspect about them that causes them to have higher ordered harmonics (at low levels, but as I pointed out earlier, the ear is very sensitive to that sort of thing) and hard clipping. The only devices that I have found that don't are the static induction transistors made by Sony. IMO They had a chance to really set the audio world forward, but in true Sony fashion (which is to come up with an innovation and then shoot themselves in the foot) failed to make a full complement of driver and voltage amplifier devices to go with their rather amazing output devices.

With such technology we could have had low distortion, zero feedback and low output impedance all at the same time!

For the most part, what I'm really hammering on is the simple fact that you can't seem to get low distortion **and** low output impedance at the same time. Now I do this in the face of the fact that many solid state amps **appear** to have very low distortion, but what research in the last 40 years has shown is that the ear has distortion on a curve of sorts; the lower ordered harmonics being unimportant to the ear and the higher ordered harmonics are really really important. I freely acknowledge that this flies in the face of the test and measurement regime, which I feel is outdated by research of the last 40-50 years.

Can you describe the sound of an amplifier by looking at its spec sheet? Most audiophiles can't; so why is there a spec sheet? The fact is most spec sheets are there to make the product look good on paper and have nothing to do with how the ear hears. That's a pretty good example of the Emperor's New Clothes...

Now if one is to say that the specs are the final arbiter, great, no worries. Have at it. But I feel that the ear, not the specs, is why we buy audio equipment and that equipment will sound better if the gear follows the rules of human hearing. 

Did you mention what your speaker brand is? I missed that bit.



 




I don't understand the comment re Melcher.  He is a neuropharmacologist.  Can you provide a citation to which of his publications you are thinking of??
Ampilfers need to have a low output impedance preferably far less than < 1ohm, otherwise they start to act like a tone control instead of being flat.

If an amplifier with high output impedance (>1ohm) were to drive these speakers there would be very little bass!! All you would get is upper-mids and highs that would fry your ears.
http://www.stereophile.com/images/1213Walexfig01.jpg

Cheers George
@georgehifi , that's correct! As I pointed out in the article, any time you mix equipment from the two technologies, the result is likely to have a tonal aberration.

The example you give is a good one, although 'fry your ears' is likely not what would happen on account of the higher impedance would result in low distortion from the amplifier. It just would not make the bass energy since designer is expecting 3 db more power output out of the amp in the bass region.

Another example is solid state driving an ESL- with the reduced impedance at high frequencies and the tendency for the load impedance to vary about 10:1 (IOW, if 10ohms at 50Hz, could be about 1 ohm at 20KHz) over its range, the result will also be too bright with not enough bass. The reason is that the impedance curve of the speaker is based on a capacitor and not a driver in a box, so the impedance curve is not also an efficiency curve.  This is quite unlike a driver in a box, where the resonance of the driver is represented by a peak in the impedance curve (IOW the impedance and efficiency curves are the same thing).

This is why the equipment matching conversation is still very much with us 5 decades on! Its also why of two amps on the bench that might measure perfectly flat to 100KHz, one might sound bright while the other does not. 

Its worth pointing out that if the designer of the speaker is expecting the amp to have a higher output impedance that the crossover will be designed differently as well. The fact that the source impedance of the amp can affect how the crossover works means that drivers might be operating outside of the area for which the designer intended! This is one of the reasons that horns got the reputation for being 'honky'.



Yes speakers manufactured back in the the old days that were "voiced" by manufacturers using tube amps with little to zero or very low damping factor amps should be used with the same with the same amps to get the frequency right as the manufacturer wanted you to hear.

But I know of no speakers for the last four to five decades that are voiced using low damping factor amps, maybe some horns or single driver Lowthers or similar.

For those that don’t know what amplifier output impedance or damping factor is
Low damping factor is high output impedance EG: more than .5ohm
High damping factor is low output impedance EG: Less than .5ohm

EG: for an amp to have a damping factor of 8 into a theoretical flat 8ohm speaker, the amp would have an output impedance of 1ohm,
If it had a damping factor of 16 the output impedance would be .5ohm
If it had a damping factor of 20 " " " " " " " .4ohm
If it had a damping factor of 100 " " " " " " " .08ohm
and so on.


Cheers George
Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.

Cheers George 
Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.
This is a common myth.

An amplifier can have a very low output impedance without having much 'current'. I put the word 'current' in quotes because Ohm's Law says without exception that the current flowing in the load is going to be directly related to the power being dissipated by the load, and that current will be the same regardless of the output impedance of the amp.

Example: 2 amps, one solid state with an output impedance of 0.1 ohm, and the other with an output impedance of 4 ohms are both making 50 watts into an 8 ohm speaker. How much current is present?

The Power formula is a derivation of Ohm's Law, and is current multiplied by voltage (1 watt = 1 Amp x 1 Volt). If you are dealing with an impedance, in this case 8 ohms, the derivation is Power = Amps(squared) x Resistance. So:

50 watts = 8Ohms x Amps squared. Solving for Amperage we get 2.5 Amps. Note that at no point does the output impedance of the amplifier figure into this- its not like an amp with a lower output impedance will somehow cause more current to flow. IOW the current is determined by the resistance of the load and how much power is being made.

Now there is the issue of the amp 'controlling' the speaker. The speaker cone moves in relationship to the energy applied to its voice coil and returns to rest when that power is taken away. What we are concerned about here is the issue of overshoot; that is to say any motion that is not having to do with the signal applied. This is where the concept of damping comes in. If the speaker is in motion and further is motion that is entirely overshoot then what happens is it will make a voltage, since there is a voice coil moving in relation to a magnetic field (this is known as 'back EMF'). That voltage has to be absorbed, and that is done by the output impedance of the amplifier, which acts as a short to that voltage.

From this you can see that the amount of current available in the amp really does not play a role in this damping effect. The output impedance however plays a huge role!

So what we can conclude is that a low current amplifier that can make the power needed will do the job as long as its output impedance is low enough to provide proper damping of the load.

FWIW, no speaker is known to need more than about 20:1 for optimal damping, and each speaker in a box (or not) has an optimal damping. For this reason back in the old days there were a number of amplifiers that had a variable damping control, which was a feedback control balancing current feedback and voltage feedback to allow the amp to have an adjustable output impedance over a wide range such that it could work with any speaker.

In the last 4 decades though there has been a race to get more and more damping factor out of amplifiers, but the effect has been to cause most loudspeakers to be over-damped. We've all heard 'tight' bass that has thump but not much in the way of definition. Its a thing that a lot of audiophiles like but its not natural- 'tight' bass does not seem to exist in real life.  When the speaker is overdamped, the cone cannot make its full excursion before the waveform starts going the other way. So bass notes in particular get truncated- the body of the bass is less prominent although the thump is there. By limiting the damping factor to no more than 20 or 30 to one this effect can be reduced or eliminated with most modern loudspeakers.
Wow, what a great post from Ralph/atmasphere. As always!
Wow, what a great post from Ralph/atmasphere. As always!
+1.

Also, while it doesn’t directly affect anything that was said in Ralph’s excellent post, to be precise I would just add that Ohm’s Law and the stated definition of power apply to resistive loads. And to the extent that a speaker’s impedance is partially capacitive or partially inductive at various frequencies the amount of current corresponding to a given power consumption by the speaker will differ somewhat from what Ohm’s Law would predict for a resistive load having the same impedance magnitude (i.e., the same number of ohms). In particular, impedance phase angles that are highly capacitive at some frequencies can increase current requirements to a significant degree, at those frequencies. But not by nearly as much as some manufacturer literature and some reviews might lead us to believe.

Best regards,
-- Al

Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.
This is a common myth.

An amplifier can have a very low output impedance without having much ’current’.
Ralph you jumped the gun mate, read again, I never tied output impedance and current output together in the same sentence.

Cheers George
I was going to write some quibbles, but instead I will just point you to this article from Roger Sanders. While the amp he talks about has long been superseded, the problems about ESL's and phase angles and currents remains true.

http://www.enjoythemusic.com/magazine/manufacture/0702/

Best,

E