John Curl's Blowtorch preamplifier part II

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Jay

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vacuphile said:
ears are never completely silent
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That's it. But not everyone realize that there is always sound/noise that you can hear. So when a signal is above the noise level, it should be possible to hear it.

At night the noise floor is so low. In the forest is more silent (it's a nice experience getting lost in the forest). But I think as long as there is wind it cannot be completely silent.

In most places like in the office at noon, there is always that "nnnngggg" high frequency sound from many switching electronics. This is the negative sound that can intrude to your music system. The source of fatigue.
 
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Jay

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wahab said:
I would question the amp rather than the latfets.
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Yes. The point is: it is harder to do it with latfet than with hexfet or bjt.

wahab said:
FTR i have a basic 2 x 120W latfet amp and it was compared to a 2 x 200W bipolar QSC amp using a bass guitar played live by the QSC owner, he just aknwoledged that the latfet was far better, and it was indeed audible as i experienced it live as well.
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I believe I will be able to know if it is true, by/from simulating the circuit. Do you think it is possible?
 
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1audio

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Kindhornman said:
bcarso,
Even the stiction would seem to be a very nonlinear function as once you get a mechanical system moving even a small amount the stiction would change functionally. In a speaker it would be the mostly the rigidity of the base resin in the spider I would imagine over the surround, but to put a percentage to that I wouldn't dare say. Add to that the non-linearity of the typical overhung voicecoil and flux density distribution and you have a combination of nonlinearities to contend with. I can compound on those with other nonlinearities but I know you do understand all the interactions that are taking place at both the lowest levels and again at the limits of output of any mechanical audio device. If we did indeed have a very linear speaker system so many of the interdependencies between the mechanical and electrical systems could actually be predicted that are now so impossible to predict by calculation alone.
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Hartley used a metal spider, sort of a flat spring. Made a lot of sense. Fiber spiders are a source of a number of issues. They change with temperature, use, time, magnitude of flex and they break down and fail over a long time.
 
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1audio

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bcarso said:
My own disposition is to use motional feedback for transducer linearization, transitioning to a "plant model"-based variable gain at higher frequencies. I pursued this for a bit and abandoned it for more pressing matters, but the absolute positional transduction approach looked very promising. I disclosed it to a transducer designer, and characteristically he said Oh I can do that by fine-tuning the motor and the suspension yada yada. I forget whether I said Well why haven't you already?
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I used position servos for subwoofers for years. Shipped quite a few. Thirty years later the customers still come to me to keep them running. Something of a curse.

It works quite well for subwoofers. At higher frequencies it all falls apart. The delay between voltage into a driver and motion on the diaphragm becomes too large to close a loop. Even in headphones.
 
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Jay

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billshurv said:
Why harder? What is hard about a device designed for Audio use vs one designed for switching use that you clearly prefer?
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Latfet is my preferred device, not switching hexfet (for certain reason).

Harder because of the low transconductance of the latfet.

Designed for audio means it is suitable (e.g. linear) for "normal" audio operation, such as low bias current. Hexfet is for switching but once you bias them very high (class-A), it turns out that they are (some of them) also suitable for audio (may be better than latfet).
 
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Jay

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DF96 said:
That taught me not to fully trust my ears, yet to 'listen' to what they were telling me.
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Max Headroom said:
I am not clear on what you mean.
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It's only words, Max...

When you meet or do business with someone new, your intuition (or brain or whatever word you want to use) tells you that you cannot trust the person.

Of course, you have to listen to your intuition while at the same time you should not fully trust your intuition... :p
 
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dvv

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I just got back from Greece last night from a cusomarily great 10 day summer vacation. Doctor's orders, my surgeon wants me well rested for the operation he must perform on my lower spine if he's to rid me of the pain produced by nerves being caught by my spine at this time for three years now. Thus, I had time to spare watching news on the TV to note that California is (again!) going through a bout of catastrophic fire north of LA.

Is everyone from the forum safe? No injuries or even loss of property I hope? It reminded me how my own woes, bad as they seem to me, are so relative compared to incomparably greater woes of others (I can hardly walk at all, and getting into and out of my car is quite a painful exercise, etc, thought actual driving is not a problem). Nothing compared to a wild forest fire in their own back yard as those people are facing.
 
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Jakob2

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billshurv said:
It does. And I am guilty of assuming on occasion that, because of the last 50 years of research we will never find a golden ear.
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All this is understandable, but the reason for scientific requirements is just the erroneous human behaviour.
Accepting methodologically flawed experiments just because you like the results does not help.

It seems that some golden ears were already found, but then always began endless debating why that could not be true. You simply can´t have it both ways... there is only one set of scientific requirements and it does not depend on the results.

DF96 said:
Interesting. To me that says that JA was happy with the Quad sound, but later sighted tests changed his opinion i.e. DBT works. I guess a true believer takes that as evidence that DBT fails, which is why you mentioned it?
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Afair JA told that he was using another amp with satisfying results in his home setup (wasn´t it a ML? ), but after attending a controlled listening test (Quad 405 in comparison with other amplifiers) where the null hypothesis was retained, he sold his amplifier and bought the Quad.
While using that, he noticed that he didn´t like the sound of his setup anymore. (at least not to the same degree as before)
After a couple of month he sold the Quad.

So he didn´t need any sighted comparisons to other amps, it was just the listening experience during "normal listening" . (The time you spend in reality with listening to music can be a good indicator indeed)
 
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DF96

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Max Headroom said:
I am not clear on what you mean.
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I mean:
- if my ears tell me it is not too bad, then it might be very bad - so check facts
- if my ears tell me it is wrong, then it might be wrong - so check facts
- if my ears tell me it is about right, then it might be about right - so check facts
In each case my ears can raise a flag, but facts determine the answer, not my ears.

Some years ago my CD player stopped working - something wrong with the actual drive. Fortunately it used a common drive so I picked up a cheap second-hand player on ebay which used the same drive, intending to swap the drives. Just for fun, I listened to the 'ebay' player - it sounded OK, although it was a cheaper model than my original player. Then I did some Googling and found that people didn't like the 'ebay' player because of the way it did the D/A. After that I found that it sounded a bit rough. So simply learning something technical about a CD player (and other peoples' opinions) affected how it sounded to me. I don't know whether it is actually fine (but now I am prejudiced against it) or if it is weak in some areas (which I am now aware of) - in either case I don't trust my ears to give me reliable information. I regard those who do trust their ears as being naive, or lacking in self-criticism; even if their ears are better than mine they are still not as good as they think they are.
 
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