John Curl's Blowtorch preamplifier part II

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But I'd argue that if you took the two examples I gave you (assuming they're identical otherwise), you'd see extremely small differences. Extremely, as their loop gain above 100 Hz would be identical.
Dear DPH,

I agree with you, of course. Close frequency corners, extremely small differences.

Very different FC ? Very different OLG ?

We are in the world of psycho-acoustic and music. No religion, no truth revealed for me. No known absolute audibility thresholds.

Some are fighting with distortion, i think VFA is the easy way, others for speed (or phase linearity at hf), CFA seems the easy way.

Anyway, like demonstrated Mr Dadod and many others, we can achieve very close results with the two topologies.
On paper.

Will they sound the same driving our speaker and, if not, witch one will we prefer ? Only oneself can answer this question. For Himself. It is not a question of "Hipe" or "High end", just a question of personal taste.

It is enough for me to open a microphone, or look at a speaker assembly to understand that "fidelity" will be a chimera. And I don't understand how so many here can talk in the name of some absolute truth with such certainties when it is about music reproduction. Certainly not the good way to be a innovative and successful designer.

Will I be burnt to the stake of heretics ?

Your humble servant,

Tryphon Tournesol.
 

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Clark Challenge official rules here: Amplifier Challenge Rules

6. To win the $10,000.00, the listener must pass two complete sessions of 12 comparisons. Passing the test means 24 correct responses.

Doesn't sound like an easy $10k to me. You have to pay to travel to his location. Pay to ship your own equipment, if that's what you want to use. It sounds quite stressful, actually. Foobar ABX sitting at home is bad enough IMHO. It may seem like it should be easy, and for gross differences it is easy. For tiny differences, its hard.

You may have seen the crowd hush when a professional golfer makes a decisive putt. How much distraction might it take to throw somebody off? I have no idea, but they seem to mostly be given the benefit of doubt.

Back to listening, I do have a reasonably good idea that I would find a double-blind sorting test preferable to a double-blind ABX test to see what I can or can't hear. Only know that from trying it a little bit as an experiment. Figuring out what it is about human brains, or my particular one, that makes it so remains a potential subject for future research. Not that anybody wants to spend money to find out.
 
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I can repeat this approach to audible accuracy vs 'like' again as we have new contributors.

The reference is the sound of real live acoustic instruments vs electronic playback in the home. Listening to a lot of musical instruments - live is needed to know and hear the difference. I/we dont compare electronics to other electronics which quickly turns into preferences.

I also record on the best recorder i can afford with minimal mics of flat response of small group of acoustic players... I am there to hear it live and then know if any changes in character occurs from mic/recording to be sure not to consider that as part of the live sound.

I have low distortion, controlled horizontal dispersion, high dynamic range speakers with flat on axis and flat power response and listen in near field conditions to minimise room effects and use best headphones (flat and low distortion).

Then, I am ready to listen or compare as to what amp is more accurate reproducer. Of course, I have ac line isolation transformers and individual ac filters et al. I'll skip all the details here.

Without a lot of live experience listening and careful attention to listening environment, it is almost impossible to know only by and A or B listening.

It also helps to have live acoustic playing in your room.... mine is large enough. Even a solo violin, cello or piano playing in your acoustic environment helps too. I have a nice white German Ritmueller kept in tune. This allows you to know the sound of live acoustic instruments in your particular acoustic environment and compare to reproduced sound of same instrument in same room.

You then keep doing this and updating gear as you find more 'accurate' pieces for 50 years and you too can tell which is the more accurate. Maybe it doesnt take 50 years but That is how long I have been at this and using this process.

And THEN, with designing, you can experiment with many factors and see if you notice a more or less accurate sound. Over time I/we have 'found' certain things to matter and incorporate into our designs.

Good luck to all,


THx-RNMarsh
 
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So you get the 'most accurate ' for your specific listening conditions, right?

No. Was that too much information?

A flat response etal and neutral environment is required to determine accuracy in equipment. AND, a knowledge of what the musical instrument actually should sound like.

Then comparison is to find the equipment which sounds most like real acoustic instruments sound -- that determines which amplifier is most accurate.

I published long ago a few things 'found' to affect accuracy. Coupling caps, for example. Electrolytic vs film caps and then to dc servo for no coupling cap. Thats an early example which affected reproduction accuracy; Millions and millions of cap upgrades in speaker xover to preamps to riaa and PA and then conceived the dc servo apps have all shown by overwhelming agreement that the sound becomes more 'accurate'. Caps, PS Zo, grounding, topologies, ac power line noise infiltration, interfacing, etc - all 'found' and studied for best solutions for improved accuracy.

Good luck in Your pursuit of accurate sound reproduction....


THx-RNMarsh
 
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I know your publications on caps etc. They were a good contribution to audio issues in the time of their origin, especially for public audience. However, now we are not speaking about electrolyte capacitors in signal path of the audio amplifier etc., at least not in our discussions.

Your approach of finding of the so called "most accurate" reproduction of sound in your specific listening room with your speakers that you described is not universal. You are not supporting your explanations by any real data collected during your tests, so it remains in "I am the expert" level. Similar as JC's approach. I know products both of yours and JC, they are good, but there are many good products of another designers and companies. It is not enough to claim experience.
 
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I know your publications on caps etc. They were a good contribution to audio issues in the time of their origin, especially for public audience. However, now we are not speaking about electrolyte capacitors in signal path of the audio amplifier etc., at least not in our discussions.

Your approach of finding of the so called "most accurate" reproduction of sound in your specific listening room with your speakers that you described is not universal. You are not supporting your explanations by any real data collected during your tests, so it remains in "I am the expert" level. Similar as JC's approach. I know products both of yours and JC, they are good, but there are many good products of another designers and companies. It is not enough to claim experience.

The process for finding problems is the same as it was for caps and then thinking of better solution -- dc servo. DC servo is my concept also. Its the process I am describing, using examples everyone is familiar with.

I have never attempted to design and build the best I could do. I am considering doing that with JC at this time. We are getting old and trade secrets and accumulated specialised knowledge could do something for the analog ages. However, it wont be cheap.

I have given my process... it is valid. Use it or not to help you get a more accurate total system of reproduction.


THx-RNMarsh
 
Pavel,

One of my observations has been that when you regularly collect data whether it be via instrumentation or your senses after a while you realize there is something going on that you previously didn't see.

In the past year two of these issues finally hit me.

The first is the source of late energy in a stadium with a distributed sound system. It seems when you space out the loudspeakers above a seating area that at very low frequencies they couple. As the seats are essentially an inclined plain, this projects the energy in a reasonable tight pattern across the field to the other side without significant attenuation as the soured size is effectively the size of the entire seating section. (The target of all those loudspeakers.) thus with 30 meter high seating sections facing each other the cross field energy may be as little as 6 dB lower than the direct energy. Thus the common practice of using multiple loudspeakers as close to the seats as possible may actually be contraindicated in some geometries. Heard first then measured.

The second is absolutely major. The original Sabine equation and all of the follow up varients use an average random instance value for acoustic absorption. This is incomplete. There are two major absorption methods. One has maximum absorption when the sound energy impinges at a nice 90 degree angle. It reasonable is decreased by the value of the cosine squared of the impinging angle. The other mechanism has maximum absorption when the impinging angle is 30 degrees.

By using the single random angle value the calculations are incorrect for different size rooms where the impingement average angle differs greatly from the materials test chamber.

My conclusion is that listening eventually will highlight a problem that can then be quantified by the right measurements. Measuring first and then trying to predict sensory response often leads to the kind of nonsense such as my THD is lower than yours so it must be better. True in gross cases not linearly applicable.
 
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