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Vintage amplifiers that could challenge or approach current state of the art amplifiers

Coach_Kaarlo

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There was a Harmon / Kardon amp, commissioned around 1980, which is by far the best I have experience with - so far.......

The owner has asked me not to mention it's model, as he is seriously hunting for another, to add to the 2 he already owns (for spares and for investment).


It had the following (taken from the company blurb);

Slew rate = 200V/us
Rise time = 1.5 us
250W into 8 ohm
440W into 4 ohm
200 amps continuous current
14,000W into 0.35 ohm load
42kg (92.5 lbs)


Design philosophies chosen for the ultimate amplifier :

1. Previous amplifiers were substandard.
2. No problem is incurable.
3. Audio is not a fashion.
4. The simpler the solution to a problem, the better .
5. The dynamic (music) state's importance over the steady (test tone) state .

6. Evaluate results with human ears, not just test equipment.

[Edit - I love these philosophies but question their modern interpretations in the Audio industry - seems many products come up well short on #5 and #6 - IMO]

But it was SOME GUYS Fifth philosophy which led to many of the discoveries and innovations incorporated in the final design. This was SOME GUYS concept of dynamic design and measurement versus the steady state. SOME GUY determined that an amplifier's performance while handling music (dynamic state) differs drastically from its performance while utilizing sine wave test tones (steady state) . The dynamic state is especially difficult to design for, because most standard and commonly understood test methods are of a steady state nature. Therefore, complex evaluation techniques and performance criteria were first created in order to test the dynamic (music) state of a given circuit design. SOME GUYS design, to achieve his ultimate goal, had to perform exceptionally well in the dynamic state.



Four Design Parameters That Make The Difference

1. High Current Capability (HCC)

The concept of the dynamic state plays an important role in the design of an amplifier's power capability. When an amplifier's power characteristics are measured by conventional test signals (steady state), it means only half the story is told. The Standard technique for measuring power output utilizes a static 8 ohm resistor to simulate a speaker system. But speaker impedances actually vary greatly according to the content of the input signal. The impedance characteristic of a loudspeaker is measured by feeding it a sine wave test tone that slowly changes in frequency. From this raw data, a "nominal" value is determined. This nominal value is the specified or rated impedance.

But, under dynamic conditions, the nominal steady state impedance rating has little relevance. The speaker system may require a huge amount of power for a very short period of time, such as a few ten-thousandths of a second. During this short period, the speaker system (2) may require the same amount of current as a 1-2 ohm resistor. It is critical that an amplifier provide the current required to give loudspeakers accurate dynamic range and transient response. This is why BLANK is designed with 200 amperes of instantaneous current capability, enabling the amplifier to react to constant impedance variations caused by the dynamic characteristics of the music signal.

BLANK delivers 14,000 watts per channel into a 0.35 ohm load under transient conditions. This dynamic power output is exclusive to BLANK!! HCC enables the amplifier to accurately control speaker cone movement by delivering the energy necessary to force the speaker cone to precisely react to transients. This performance has significant importance in high fidelity reproduction.

2. Phase Intermodulation Distortion (PIM)
Phase intermodulation distortion can be an unwanted by-product of negative feedback. Negative feedback, which is used in every amplifier, routes part of the output signal back to the input, 180 degrees out-of-phase with the original signal. The combination of these two signals, out-of-phase with each other, creates an error - correction signal that greatly reduces the steady state harmonic distortion inherent in the amplifier. However, a high amount of negative feedback creates a high (and very audible) amount of Phase Intermodulation distortion (PIM) in place of the harmonic distortion it eliminates. This was proven by SOME GUY and presented to the Audio Engineering Society in 1980 at a convention in Hamburg. Since negative feedback merely transforms one type of distortion to another, the BLANK is designed to have minimal inherent distortion. The result is very low PIM and THD.

3. Interface Intermodulation Distortion (IIM)
Interface Intermodulation Distortion , or IIM in abbreviated form, occurs in the speaker/amplifier interface. The moving cone and coil structure in the speaker generates its own voltage which returns to the output stage of the amplifier. This voltage is called the Back Electromotive Force (Back EMF). Once this voltage passes the output stage, it travels through the negative feedback circuit and returns to the input stage where it combines with the input signal. This mixing of the legitimate musical input signal and the Back EMF speaker generated signal results in increased dynamic distortion. This creates excessive IIM which results in an obscured lower mid-range, which makes the sound appear vague and lacking in definition. The minimization of IIM in BLANK is carried out by reducing the negative feedback, and by decreasing the internal resistance of the output stage. The result is that BLANK has clear mid and low frequency reproduction, which is pure and well balanced.

4. Transient Intermodulation Distortion (TIM)
Transient Intermodulation Distortion or TIM, as it is referred to, occurs when fast transients - such as in dynamic music passages - pass through an amplification stage prior to the return of the output signal via the negative feedback. These transients then overload the first stage sufficiently to cause internal clipping - hence, TIM.

The BLANK counters the negative aspects of TIM with three special design parameters:
A. The BLANK utilizes a super-low distortion driver stage which exhibits localized feedback (feedback within each stage versus feedback around the entire circuit).
B. The introduction of transistors with extremely quick response speed, excellent linearity, and a large, safe operating area.
C. The incorporation of a dual power supply system with high and low voltage sources. The high voltage source, dedicated to the driver , has the ability to supply the proper voltage under any condition .

Controlling negative feedback and utilization of circuitry not dependent on negative feedback enables the BLANK to virtually eliminate TIM.



[Edit - some interesting facts about the boards]

(A) Normally , the circuit boards in an amplifier's audio signal path are made either of phenolic or fiberglass material. When the amplifier heats up, it causes these circuit boards to expand and "flex " which degrades the mechanical integrity and can increase distortion.
(B) BLANK hybrid circuit boards are made of ground sapphire, which like diamond, is extremely rigid, and does not expand or flex when heated. This eliminates mechanical stress on the circuitry which ensures long-term reliability.
(C) The metal-film resistors in BLANK circuitry are made of silver palladium , a rare earth metal which never corrodes thereby keeping resistor values perfect forever.
 

SIY

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My goodness.
 
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restorer-john

restorer-john

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Gentlemen, I give you the Citation XX.

1597889143172.png


Its little crate:
1597889226166.png


Try a hard question...

It was the most expensive amplifier I recall listed at the time in 1983 @ AU$15,300
 

Coach_Kaarlo

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restorer-john

restorer-john

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What did you think of it John?? Presumably you listened to or measured one at some point?

It was magnificent. I saw one (and the XXP with clear perspex tops) and the rest of the range at an audio show (it was flown out for the show) in around 1983 or 1984. I was still a teenager and it was the stuff of dreams. I didn't hear it and have never seen one in Australia since, letalone worked on one.

There are a few floating around in the US for sure and not as expensive as you'd think.

The series from 1983/4/5 from HK are still benchmarks in my experience and I have collected a number of the integrated amplifiers. In fact, strangely enough, I just pulled out my favourite 50wpc amplifier, the PM-650 (two of them) from my storeroom and I've listening to it for the past week.

scan491.jpg


At the time, my best mate lashed out and bought a HK PM-660 (and a CD-291/TU-615 and Infinity RS-5Bs). He still has the RS-5Bs. I bought a Sansui AU-D5 which my father still has in his collection.
 
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restorer-john

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@Coach_Kaarlo I would be looking to find units destined for Germany and the continent or if they made units for the military. They come with true multivoltage transformers. You don't want a 120V unit and a stepdown for Australia.

It is important with those really big amps to get it right.

You also should consider our nominal voltage is now 230V, not the 240V it was back then. Most of the HK gear came to us tapped from the EU destined production and was nominally 220V. Some HK gear had 4 tappings (110,120,220,240) some was two tappings 110/120,220/240V. Depending on where he lives in AU, his line voltage could be 250V or 220V. Most of the eastern seaboard has switched to a nominal 230V including VIC/NSW and most of QLD.

People don't consider the effects of line voltage until things start failing prematurely.

(I had a 20V average drop only the other month when a transformer tap was changed in my street and all the others around me. I got the power company out after logging my own readings and they put monitors up on the pole, the panel and a few in the street. A week later, they reset the tap and told me exactly what I knew- it was well outside the tolerance and significantly below nominal. Solar is causing all sorts of trouble due to feed in voltage differentials)

Makes a huge difference when testing amplifier power outputs. I didn't want to break out the variac everytime or that noisy old ferroresonant transformer that weighs a ton.
 
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Coach_Kaarlo

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It was magnificent. I saw one (and the XXP with clear perspex tops) and the rest of the range at an audio show (it was flown out for the show) in around 1983 or 1984. I was still a teenager and it was the stuff of dreams. I didn't hear it and have never seen one in Australia since, letalone worked on one.

There are a few floating around in the US for sure and not as expensive as you'd think.

The series from 1983/4/5 from HK are still benchmarks in my experience and I have collected a number of the integrated amplifiers. In fact, strangely enough, I just pulled out my favourite 50wpc amplifier, the PM-650 (two of them) from my storeroom and I've listening to it for the past week.

View attachment 78954

At the time, my best mate lashed out and bought a HK PM-660 (and a CD-291/TU-615 and Infinity RS-5Bs). He still has the RS-5Bs. I bought a Sansui AU-D5 which my father still has in his collection.


If you are ever in Sydney (COVID etc) I can connect you with the owner for a listening session in his studio. We tested for 6 hours per session, on 2 occasions (level matched listening and cone excursion but nothing more serious - just focusing on specific musical passages a few seconds long and repeating them). I was interested how it performed against my 2 Benchmark Media AHB2's in mono (comparable output).

The AHB2's had great imaging and clarity - but nothing close on the dynamics. There are a whole string of unanswered questions in my mind regarding measuring the AHB2 dynamically to understand why they sound so different dynamically and yet measure so well statically. But let's just say if the owner had been interested in selling I would have purchased speakers AND an amp that day.

If you know of a few of these in the US that aren't too expensive send me a PM, I would be interested in purchasing one myself but was put off by what I understood current market value was - circa AUD20k.
 

Coach_Kaarlo

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@Coach_Kaarlo I would be looking to find units destined for Germany and the continent or if they made units for the military. They come with true multivoltage transformers. You don't want a 120V unit and a stepdown for Australia.

It is important with those really big amps to get it right.

You also should consider our nominal voltage is now 230V, not the 240V it was back then. Most of the HK gear came to us tapped from the EU destined production and was nominally 220V. Some HK gear had 4 tappings (110,120,220,240) some was two tappings 110/120,220/240V. Depending on where he lives in AU, his line voltage could be 250V or 220V. Most of the eastern seaboard has switched to a nominal 230V including VIC/NSW and most of QLD.

People don't consider the effects of line voltage until things start failing prematurely.

Crossed messages!

Thanks for the tip!! Will also pass on to my friend.

[Edit; he has the 110V version and a small transformer see pic]
 

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anmpr1

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1. High Current Capability (HCC)
2. Phase Intermodulation Distortion (PIM)

Phase intermodulation distortion can be an unwanted by-product of negative feedback. Negative feedback, which is used in every amplifier, routes part of the output signal back to the input, 180 degrees out-of-phase...
3. Interface Intermodulation Distortion (IIM)
Interface Intermodulation Distortion , or IIM in abbreviated form, occurs in the speaker/amplifier interface.
4. Transient Intermodulation Distortion (TIM)

1) The question is, how 'high' is high? As previously mentioned in an example, if your loudspeaker is a small box (or an electrostatic) with high nominal impedance, you don't need a lot of current, but a lot of voltage. It's why the monster current ML-2 clipped driving the Tangent loudspeaker while a tube based limited current H3aa drove the speaker to high SPL. For a typical 8 ohm speaker in a typical living room, listening at typical levels, you don't need a Krell amp (or a Citation XX). Don't misunderstand--that doesn't mean that you wouldn't like to own a Krell or Citation, and it certainly doesn't mean that more power isn't worth having, just in case.

2) NFB has been beaten to death since the early '70s. Some amps using a 'lot' of NFB were reported to sound very good, such as the H3aa. There are numerous posts about NFB here at ASR, just for the asking.

3) Bob Cordell wrote about this. Yandex 'Cordell IID' for links. In one of his papers the IID discrepancy between two 'test' amps was spread between 0.1% and 0.3% IID, and in another 0.052% v 0.063%. I'd be a fool to question someone as schooled as Bob Cordell, but I'd question him as to whether any of his findings have any actual basis for audibility under 'controlled' listening conditions. However that is, like most measurable distortions, on an absolute level I guess less is more.

4) See my reply #2

I'm always a tad skeptical when a manufacturer touts a specific set of rather 'esoteric' measurements as the latest and greatest 'final solution' to the 'amplifier problem'. Before getting too excited over it I first grab my Marketing 101 textbook in order to get more details.
 
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Coach_Kaarlo

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1) The question is, how 'high' is high? As previously mentioned in an example, if your loudspeaker is a small box (or an electrostatic) with high nominal impedance, you don't need a lot of current, but a lot of voltage. It's why the monster current ML-2 clipped driving the Tangent loudspeaker while a tube based limited current H3aa drove the speaker to high SPL. For a typical 8 ohm speaker in a typical living room, listening at typical levels, you don't need a Krell amp (or a Citation XX). Don't misunderstand--that doesn't mean that you wouldn't like to own a Krell or Citation, and it certainly doesn't mean that more power isn't worth having, just in case.

2) NFB has been beaten to death since the early '70s. Some amps using a 'lot' of NFB were reported to sound very good, such as the H3aa. There are numerous posts about NFB here at ASR, just for the asking.

3) Bob Cordell wrote about this. Yandex 'Cordell IID' for links. In one of his papers the IID discrepancy between two 'test' amps was spread between 0.1% and 0.3% IID, and in another 0.052% v 0.063%. I'd be a fool to question someone as schooled as Bob Cordell, but I'd question him as to whether any of his findings have any actual basis for audibility under 'controlled' listening conditions. However that is, like most measurable distortions, on an absolute level I guess less is more.

4) See my reply #2

I'm always a tad skeptical when a manufacturer touts a specific set of rather 'esoteric' measurements as the latest and greatest 'final solution' to the 'amplifier problem'. Before getting too excited over it I first grab my Marketing 101 textbook in order to get more details.

Interesting points. Yes the blurb is just that - marketing blurb.

However I do like the design philosophy mentioned, particularly the last 2.

5. The dynamic (music) state's importance over the steady (test tone) state .
6. Evaluate results with human ears, not just test equipment.

Do you think the dynamic performance of modern amps is equivalent to vintage amps in general? Do you think engineers evaluate using blind tested ears as well as measurements? Seems like dynamic performance is costly and difficult to measure well, and most manufacturers work to static performance these days. Of everything I wrote this is the thing I am most interested in - particularly because I have experienced the differenCe dynamically between the HK amp and the AHB2 first hand.
 

anmpr1

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5. The dynamic (music) state's importance over the steady (test tone) state .
6. Evaluate results with human ears, not just test equipment.

Do you think the dynamic performance of modern amps is equivalent to vintage amps in general? Do you think engineers evaluate using blind tested ears as well as measurements? Seems like dynamic performance is costly and difficult to measure well, and most manufacturers work to static performance these days. Of everything I wrote this is the thing I am most interested in - particularly because I have experienced the differenCe dynamically between the HK amp and the AHB2 first hand.

There is no doubt at all that dynamic conditions are 'real world' and steady state measurements are 'contrived'. Unless your idea of music is test tones.

My guess is that if amplifiers 'sound different' it is not something intrinsic or 'inside' the amplifier (as most subjective reviewers would have you believe) but rather the electrical properties at the amplifer/lousdpeaker interface causing FR and/or other distortion errors (to include clipping as in the Tangent-ML-2 real world example). That is why you need a Krell if your idea of a living room speaker is the one ohm Apogee.

The problem with listening tests as a 'final' measure of goodness is that it's easy to fool yourself by attributing something real to an actually non-existent 'perception'. The same thing can sound 'different' on different days, at different times of the day, and even depending upon how you 'feel' that day, or how you concentrate on a particular musical passage. This is really in the realm of psychology and not psycho-acoustics.

FWIW, as I've stated in other threads, I immediately 'heard' the difference between my AHB2 and Dyna Mk IV. There are plausible reasons for that--one being a that the Dyna is a 1960 tube design I built myself. Check out @amirm test of the Dyna ST-70 (essentially two Mk IV amps on one chassis) to see why this might be so.

Whether I could hear a difference between the AHB2 and my Yamaha AX-592, with levels matched?

https://www.audiosciencereview.com/forum/index.php?threads/catalogue-of-blind-tests.8675/post-217462
 
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restorer-john

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Do you think the dynamic performance of modern amps is equivalent to vintage amps in general? Do you think engineers evaluate using blind tested ears as well as measurements? Seems like dynamic performance is costly and difficult to measure well, and most manufacturers work to static performance these days. Of everything I wrote this is the thing I am most interested in - particularly because I have experienced the differenCe dynamically between the HK amp and the AHB2 first hand.

The Citation XX is running much higher voltage rails with significantly more transformer and power supply capacity than the Benchmark. Even in bridge mode, the Citation would have the edge in available voltage swing. And into low impedances, the bridged Benchmark will not come close to ability of the XX.

That said, the Benchmark will likely be a quieter amplifier in terms of residual noise. It appears to have ~20dB advantage.
 

Wes

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what about the famed old Dynaco tube amps?
 

Coach_Kaarlo

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There is no doubt at all that dynamic conditions are 'real world' and steady state measurements are 'contrived'. Unless your idea of music is test tones.

My guess is that if amplifiers 'sound different' it is not something intrinsic or 'inside' the amplifier (as most subjective reviewers would have you believe) but rather the electrical properties at the amplifer/lousdpeaker interface causing FR and/or other distortion errors (to include clipping as in the Tangent-ML-2 real world example). That is why you need a Krell if your idea of a living room speaker is the one ohm Apogee.

The problem with listening tests as a 'final' measure of goodness is that it's easy to fool yourself by attributing something real to an actually non-existent 'perception'. The same thing can sound 'different' on different days, at different times of the day, and even depending upon how you 'feel' that day, or how you concentrate on a particular musical passage. This is really in the realm of psychology and not psycho-acoustics.

FWIW, as I've stated in other threads, I immediately 'heard' the difference between my AHB2 and Dyna Mk IV. There are plausible reasons for that--one being a that the Dyna is a 1960 tube design I built myself. Check out @amirm test of the Dyna ST-70 (essentially two Mk IV amps on one chassis) to see why this might be so.

Whether I could hear a difference between the AHB2 and my Yamaha AX-592, with levels matched?

https://www.audiosciencereview.com/forum/index.php?threads/catalogue-of-blind-tests.8675/post-217462


Benchmark Media quote: “The truth lies here: Specifications must be measured under typical operating conditions if they are to be useful in predicting audible differences.”

Ok, my lack of clarity = you missing my point. We are completely on the same page regarding sighted or bias led testing and true blind unsighted scientific testing - see my posts on the Frailty of Sighted Listening. And again we are on the same page that biases of many kinds cloud our judgement and make us think we hear things we don't etc. However as a trained Engineer I would be out of work if I was unable to solve complex problems with incomplete information - particularly when working in R&D where we are inventing new technology - so I know a little about critical thinking and logical methodical problem solving using the scientific method.

I agree that listening tests are merely a confirmation of measurements, but no less important to conduct (blinded).

So it seems to me there is a hierarchy of differences in the sound a system produces;
  • 1 = what can be heard in blind testing by a reasonable sample size
  • 2 = what can be heard and measured (some audible differences are difficult to measure because we would first have to be able to define or describe what we were hearing - meaning listener identified the difference correctly but was unable to describe what was different)
  • 3 = what can be measured but not heard explicitly or easily in blind testing but which still matters (noise, distortion, etc)
  • 4 = what can be measured dynamically (almost always matters)
  • 5 = what can be measured statically (that actually matters)

So here are my thoughts (based on your post);
  1. Any discussion on these amplifier sound topics is fraught unless the amplifier and speakers (and room) are considered as a system, because based on what I have learnt, here on ASR and through reading Toole Olive et al, some of the biggest audible and measurable differences come from the interactions between these components.
  2. Not being able to explain repeatable, measurable, perceivable differences with scientific data does not preclude their veracity - it just means often the understanding, research, engineering knowledge, scientific modeling have not been done or the studies to date have not considered the problem one is seeking to solve or understand. Most true breakthroughs and innovations were considered ludicrous and magical by the establishment until they were proven, and then subsequently widely repeated, and finally adopted as the norm. - ummmmm refer history and science.....
  3. As I mentioned in my original AHB2 post regarding dynamic performance - repeat my test then comment - the differences between the following will be apparent to anyone without profound hearing loss or substance based impairment;
    1. TEST =HK Citation XX + same cables + same speakers + same room + same levels + same program material
    2. TEST =AHB2 (stereo and mono) + same cables + same speakers + same room + same levels + same program material
    3. TEST =Accuphase P300 + same cables + same speakers + same room + same levels + same program material
    4. TEST = Sennheiser HD650 + DAC2-HGC + ears + approximate level (not same) + same program material
  4. WHY these differences exist and what the causes of the differences are is hard to ascertain IMO without an open mind, time, money, and equipment. As @GXAlan and @restorer-john have pointed out both here and on the AHB2 thread, there are big, fundamental, specification differences between the AHB2 and the older vintage style amplifiers we were testing. As Alan and John both allude there are differences between the dynamic capacity of these amps which with some combinations (speakers + amp) which will probably be measurable, and perhaps even audible. Certainly we were able to hear, and see (cone extension), and feel (kick drum etc) the dynamic difference.

The Citation XX is running much higher voltage rails with significantly more transformer and power supply capacity than the Benchmark. Even in bridge mode, the Citation would have the edge in available voltage swing. And into low impedances, the bridged Benchmark will not come close to ability of the XX.

That said, the Benchmark will likely be a quieter amplifier in terms of residual noise. It appears to have ~20dB advantage.

Hi John, yes this was my experience, and it left me wondering if the big old heavy 13 inch woofers of the NS_2K speakers where asking for a bit much current from the little AHB2's. And or the rise time/ slew rate numbers of the AHB2 were also contributing. What I mean is I wonder if I changing the speaker part of the equation to something smaller, more efficient but still able to play loud, whether the AHB2 will perform closer to the XX or P300 (or similar old gems). I searched for a while to grab these NS-2000's because in my understanding they are very good even by modern standards, the FR measures well, realistically voiced, and their off axis directivity measures very very well - but maybe they are just to big and heavy for the little AHB2 amp?

And yes if I listened to residual noise I would be content - but I prefer music which is dynamic in nature and therefore difficult to reproduce.

Seems like the Benchmark Media logic applied to measuring the dynamic loads on head phones, and the subsequent clear results of how different dynamic loads are to static loads, indicate to me that measuring amplifiers in static conditions is almost utterly pointless. Not unlike using nominal impedance for speakers.

Honestly, in one breath knowledgeable members on this forum acknowledge the challenging dynamic requirements on the amplifier to drive a loudspeaker accurately - then in the next breath present endless measurements of static steady state conditions and loads as proof of what they are hearing or not hearing from an amplifier.
 
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Harmonie

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Benchmark Media quote: “The truth lies here: Specifications must be measured under typical operating conditions if they are to be useful in predicting audible differences.”

Ok, my lack of clarity = you missing my point. We are completely on the same page regarding sighted or bias led testing and true blind unsighted scientific testing - see my posts on the Frailty of Sighted Listening. And again we are on the same page that biases of many kinds cloud our judgement and make us think we hear things we don't etc. However as a trained Engineer I would be out of work if I was unable to solve complex problems with incomplete information - particularly when working in R&D where we are inventing new technology - so I know a little about critical thinking and logical methodical problem solving using the scientific method.

I agree that listening tests are merely a confirmation of measurements, but no less important to conduct (blinded).

So it seems to me there is a hierarchy of differences in the sound a system produces;
  • 1 = what can be heard in blind testing by a reasonable sample size
  • 2 = what can be heard and measured (some audible differences are difficult to measure because we would first have to be able to define or describe what we were hearing - meaning listener identified the difference correctly but was unable to describe what was different)
  • 3 = what can be measured but not heard explicitly or easily in blind testing but which still matters (noise, distortion, etc)
  • 4 = what can be measured dynamically (almost always matters)
  • 5 = what can be measured statically (that actually matters)

So here are my thoughts (based on your post);
  1. Any discussion on these amplifier sound topics is fraught unless the amplifier and speakers (and room) are considered as a system, because based on what I have learnt, here on ASR and through reading Toole Olive et al, some of the biggest audible and measurable differences come from the interactions between these components.
  2. Not being able to explain repeatable, measurable, perceivable differences with scientific data does not preclude their veracity - it just means often the understanding, research, engineering knowledge, scientific modeling have not been done or the studies to date have not considered the problem one is seeking to solve or understand. Most true breakthroughs and innovations were considered ludicrous and magical by the establishment until they were proven, and then subsequently widely repeated, and finally adopted as the norm. - ummmmm refer history and science.....
  3. As I mentioned in my original AHB2 post regarding dynamic performance - repeat my test then comment - the differences between the following will be apparent to anyone without profound hearing loss or substance based impairment;
    1. TEST =HK Citation XX + same cables + same speakers + same room + same levels + same program material
    2. TEST =AHB2 (stereo and mono) + same cables + same speakers + same room + same levels + same program material
    3. TEST =Accuphase P300 + same cables + same speakers + same room + same levels + same program material
    4. TEST = Sennheiser HD650 + DAC2-HGC + ears + approximate level (not same) + same program material
  4. WHY these differences exist and what the causes of the differences are is hard to ascertain IMO without an open mind, time, money, and equipment. As @GXAlan and @restorer-john have pointed out both here and on the AHB2 thread, there are big, fundamental, specification differences between the AHB2 and the older vintage style amplifiers we were testing. As Alan and John both allude there are differences between the dynamic capacity of these amps which with some combinations (speakers + amp) which will probably be measurable, and perhaps even audible. Certainly we were able to hear, and see (cone extension), and feel (kick drum etc) the dynamic difference.



Hi John, yes this was my experience, and it left me wondering if the big old heavy 13 inch woofers of the NS_2K speakers where asking for a bit much current from the little AHB2's. And or the rise time/ slew rate numbers of the AHB2 were also contributing. What I mean is I wonder if I changing the speaker part of the equation to something smaller, more efficient but still able to play loud, whether the AHB2 will perform closer to the XX or P300 (or similar old gems). I searched for a while to grab these NS-2000's because in my understanding they are very good even by modern standards, the FR measures well, realistically voiced, and their off axis directivity measures very very well - but maybe they are just to big and heavy for the little AHB2 amp?

And yes if I listened to residual noise I would be content - but I prefer music which is dynamic in nature and therefore difficult to reproduce.

Seems like the Benchmark Media logic applied to measuring the dynamic loads on head phones, and the subsequent clear results of how different dynamic loads are to static loads, indicate to me that measuring amplifiers in static conditions is almost utterly pointless. Not unlike using nominal impedance for speakers.

Honestly, in one breath knowledgeable members on this forum acknowledge the challenging dynamic requirements on the amplifier to drive a loudspeaker accurately - then in the next breath present endless measurements of static steady state conditions and loads as proof of what they are hearing or not hearing from an amplifier.

Nothing, don't bother , it's just for me to keep this post in my personal files.
Teach me if there is another way doing it.
 

Mnyb

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The Norwegian Brand Dynamic Precision comes to mind found data on thier DPA 6.4 online .
This is not even thier most impresive amp i think they made ones with even lower distorsion , but i think they are out off bussines.

1598007908839.png


Sorry for the messy formating finding data on some online pdf manual download site
 

anmpr1

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Benchmark Media quote: “The truth lies here: Specifications must be measured under typical operating conditions if they are to be useful in predicting audible differences.”

Seems like the Benchmark Media logic applied to measuring the dynamic loads on head phones, and the subsequent clear results of how different dynamic loads are to static loads, indicate to me that measuring amplifiers in static conditions is almost utterly pointless. Not unlike using nominal impedance for speakers.

Honestly, in one breath knowledgeable members on this forum acknowledge the challenging dynamic requirements on the amplifier to drive a loudspeaker accurately - then in the next breath present endless measurements of static steady state conditions and loads as proof of what they are hearing or not hearing from an amplifier.

Benchmark is a respectable and engineering based organization. At the same time they have to sell product to fickle audiophiles, both amateur and professional. So they sometimes straddle the fence.

Steady state measurements are good enough if the amplifier is good enough--that is, if your loudspeakers don't present a weird and unpredictable load. Transient measurements are fine, but as in the case with Bob Cordell, Marshall Leach, Matti Otala and others, you have to ask yourself whether their measurement protocols (which show up very real and measurable differences) have anything at all to do with what can be heard, above and beyond steady state measurements.

In the Tom Holman Advent receiver thread we discussed his (and others') measurements on dynamic distortions as they might concern audible differences in preamplifier circuits. Peter Aczel measured a handful of preamps (two dozen) and found absolutely no correlation among those esoteric tests and how they 'sounded' in subjective auditions. Not long afterwards, Holman himself walked away from his dynamic protocols, deciding it wasn't important. The point is, clever practitioners can always find some or another 'test' to measure differences in circuits. That is not the point. The point is, does any of it make any difference?

FWIW Peter told me that all those 'audible differences' back in 1977 were likely due to his sloppy protocol of not matching levels. I argued that given his front and back end (expensive MC cartridges on expensive turntables and electrostatic loudspeakers) that possibly there were differences. He was not impressed with my argument, and acted as if I hadn't learned anything at all. LOL

Until anyone can prove otherwise I have to subscribe to what he wrote 30 years after his big amp shoot outs:

Any amplifier, regardless of topology, can be treated as a “black box” for the purpose of listening comparisons. If amplifiers A and B both have flat frequency response, low noise floor, reasonably low distortion, high input impedance, low output impedance, and are not clipped, they will be indistinguishable in sound at matched levels no matter what’s inside them.
 

Pluto

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I would love to see one of the Quad current dumpers measured.
There are so many of these units in everyday service, I doubt it would be possible to estimate just how populous they are.

If the clones of the 405 amplifier modules, typically available for <$50 a pair, are anywhere as good as the real thing, you have a total bargain.
 
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