John Curl's Blowtorch preamplifier part III

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Why this ? I don't believe the major difference between the two topologies is about the slew rates, As most of the modern OPAs are fast enough, but their compressive VS expansive behaviors.
Hi T, what do you mean by compressive VS expansive behaviours and how do these 'characteristics' manifest subjectively ?.

People, here, are all situated on a social line between very few that believe in Magic and Voodoo and those who believe that measurements tells everything in audio, no listening out of ABX etc.
So what is this 'Magic and Voodoo'.....is this label for observations that are not readily explained by 'high school physics' and contradict entrenched belief systems ?.

I noticed that the people situated between the middle and the right of this line are the most intolerant aggressive and impolite ones. Why ? Pseudo science makes people frustrated ?
People get upset when entrenched belief systems are revealed as belief systems.


Dan.
 
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And I asked myself a question. The designers that are at the right of this line do not listen to their changes at each step of their work ? Or do they listen music via LTSpice and co ? And, if they do listen on their bench, do-they really set an abx process at each listening to ensure any progress ? Honestly !

Most likely don't feel the need often for any listening tests, as they are convinced that the numbers tell the whole story.

Further, some are not interested in "boring, blind tests" at all, while others obviously think, that if the results are as expected, no controlled listening tests (even "blinded" ) are needed.

Impression based on a not so large sample size and of course will not be correct for everyone of the group. 🙂
 
Most likely don't feel the need often for any listening tests, as they are convinced that the numbers tell the whole story.
. 🙂

The more I learn of this industry the more things fall into place.......I’ve heard some horrific offerings in ‘high end’ audio over the years and came away saying to myself, ‘self.....doesn’t anybody even listen to this stuff between design and showroom floor?’ ..... Surely they must.

but maybe not! 🙁
 
A good guide to this attitude re measurements is to be found on AudioScienceReview (ASR) where most of the members are now filtered/self-selected into those who regard measurements as the only truth - you will find few if any subjective impressions posted without challenge

I doubt anyone would categorize Bruno Putzeys as a subjectivist or doubt his design chops when it comes to digital audio yet he has this to say about measurements which appears eminently sensible to me.

Please don't dismiss with the usual filthy lucre objection "of course he is trying to sell his designs" This guy has designed many class D modules that are used here in DIY designs - there's no doubting his abilities. Let's just try to keep this a technical discussion, for a change!

Read these answers & more here

Q "So how do these new amps sound? What is your goal around sound?"

"Bruno: No sound at all. The output signal should be indistinguishable, by ear, from the input signal. I’m stressing the “by ear” thing here because we as audio nerds, and that includes all interviewers here, are often conflicted about what it means to measure and what it means to listen. For me, measurements are lab tools. Measurements tell you technically what your circuit is doing. Before you heat up your soldering iron to, say, change a resistor, you need to have something numerical to point to the right resistance value. Ears don’t help there. Your ear should be used instead to figure out what to measure so as to make those measurements meaningful for sound quality.

Bruno: What I also need to get off my chest here is the confusion between accuracy and clinical “analytical” sound. What’s implied there is that you have to choose between accuracy and joy. That runs completely counter to my experience. When something sounds “clinical” or “analytical” it always turns out to be totally inaccurate. Overhyped highs and thin mids have nothing to do with accuracy. An accurate system will sound warm, lush and emotionally engaging provided that these characteristics are actually in the recording. Low distortion sound can be incredibly moving.

Q: "Now that THD measurements have been driven so low, what else are you hoping to achieve in this and future designs that relate to the unmeasured quality of the sound of Hi Fi amplification gear? Not looking for a high level debate about measurements, but I am assuming that not everything related to SQ has been measured and/or is not seen in the standard measurements."

Bruno: I like the way you put it, “unmeasured”. Because that’s really the point when measurements and ears diverge. Measurements are scientific experiments: to test a hypothesis. Remember that you can’t ever prove a hypothesis, the best thing you can do is try very, very hard to disprove it. Every time you fail to prove your hypothesis false, it becomes more solid. So if your hypothesis is that “this is a good amplifier” you try to make it do things you don’t want it to do. It’s not enough to run a handful of standardised tests, you have to invent all sorts of tests that you target specifically at weaknesses you expect.

And just to show that I'm open minded about sine wave testing Vs dynamic signal testing here's his quote that somewhat contradicts me
Bruno: The nice thing is that this high frequency IMD test is about the worst thing you do to an amp with an input that’s still technically an audio signal. Of course you can make an amplifier go completely mad by feeding it radio frequency signals but that’s not going to tell you anything about the sound. But to come back to your question, I’m always looking for test methods that are within the remit of audio and that somehow make amplifiers do unexpected things. Admittedly that well has dried up a little. Even a class D amplifier is simple enough that with two sine waves you can pretty much probe all there is to probe. The only real surprise we had recently was to do with the output choke. Magnetic materials have something called hysteresis, but there is precious little information about what this really does. If you test a magnetic core with a sinewave the distortion looks a little like soft clipping, perfectly benign. But what came out of tests on iron parts in loudspeakers was that hysteresis has a long term memory so you can get intermodulation between things that happen now and things that happened 10 minutes ago. With music this distortion sounds like half correlated noise.
 
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And I asked myself a question. The designers that are at the right of this line do not listen to their changes at each step of their work ? Or do they listen music via LTSpice and co ? And, if they do listen on their bench, do-they really set an abx process at each listening to ensure any progress ? Honestly !
It depends on what kind of designer.....the newly out of university LTSpice expert EE will know that his design is electrically ideal and will be reliable but likely does not know what to listen for if ever appraising his creation.
The experienced audio dedicated designer will utilise Spice/CAD in a different way and will of course audition thoroughly and against known references.
I have zero doubt that the likes of Sony ES Series design team (ditto other mfrs) audition and finesse their work......to not do so would be commercial harakiri.

Oh, BTW, Evenharmonics, could-you stop with your "Matched level" obsession ?We all practice-it as a basic requisite (since more 50 years for me) !
Yup we have all been around long enough to just do this automatically.
Another thing we do is see how far we can push systems before they fall apart subjectively.
Us old guys also listen with out ears and NOT our eyes so enough of the ABX pollution please everybody.
 
Well, that is just too bad for you then.

For myself and Mark, and maybe some other, it is helpful data point to know if doing such Hf absorption and additional shielding.... can it make any detectable difference and we will continue to improve our designs and modifications and evaluate new ideas. As well as T&M and listening.

Enjoy.

THx-RNMarsh
It would have been extremely useful if you had not missed this opportunity to use an array of measuring equipment to spot any effects of the treatment and had done the listening tests properly.

I am sure you and Mark enjoyed yourself, but you did not learn anything useful. Nor can you pass any knowledge on to us. It is just an anacdote of two guys sitting in a room playing with expensive toys.

In the fullness of time and upon further reflection on what you did, I am sure you will come round to my point and realize how presumptuous your claims in the post that triggered all this really are.
 
It would have been extremely useful if you had not missed this opportunity to use an array of measuring equipment to spot any effects of the treatment and had done the listening tests properly.

As Markw4 already mentioned in his post about the meeting that RNMarsh's measurement equipment was already shipped to the new destination, wouldn't it be a good idea to ask if it would have even been possible to do a thorough measurement session when the device came back?

In the fullness of time and upon further reflection on what you did, I am sure you will come round to my point and realize how presumptuous your claims in the post that triggered all this really are.

And if you would take some of this "(self)reflection" medicine, couldn't it be that a large portion of your post(s) on this topic is just based on bias/strong belief? (assumed that you hadn't recently bought a perfectly working crystal ball 🙂 )
 
Hi T, what do you mean by compressive VS expansive behaviours and how do these 'characteristics' manifest subjectively ?.
"Current on demand" for CFA.

I will not take the risk to share my personal "subjective" sympathies ;-) as it is never good to generalize.
 

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In the fullness of time and upon further reflection on what you did, I am sure you will come round to my point and realize how presumptuous your claims in the post that triggered all this really are.

Probably not. The problem you seem to have is that you weren't there to hear the obvious for yourself, and you do not trust us not to be fooled. It comes down to trust or the lack thereof.

It does seem a bit odd that you don't know or haven't looked around to find some skilled listeners in or around your locale. If you don't believe such can exist, then of course you wouldn't look. But, such people do exist even if outside of your experience, and we happen to be pretty good at it.

You may have read in this thread where Nelson Pass said that Jam, "still has one of the best pairs of ears in the business." The very popular and good sounding Pass Labs HPA-1 was designed by Jam. Many listening tests were done to fine tune the exact sound. You may believe that is possible or not, but it happens to be quite possible, IME.

Also, since Jam is a friend and we sometimes listen together, we have found we hear just about the same way. We have come to trust each other's listening reports because experience has shown that if one of finds a problem there is indeed a problem.

However, I get that since you don't have a skilled listener at your disposal, maybe because you don't want to have one, you cannot replicate anything that we tell you, there in your own lab. Since you are not the trusting type, your own replication is all that is meaningful to you. So it seems anyway. However, perhaps there is more to it than the way it looks from here.
 
If I'd assert the opposite, means taking bias-based assumptions as facts would most likely have lead to a completely failure of the "man on the moon" mission....?

Btw, is there an answer to the first question in my previous post?

No no no, you nasty word twister, that is not what I said. My strong bias is towards the scientific method. It is the only way to keep us out of the woods. My belief is that if you follow the laws of nature, stuff will behave predictably.

And may I reply to your rethorical question with another one?
 
"Current on demand" for CFA.
I will not take the risk to share my personal "subjective" sympathies ;-) as it is never good to generalize.
I don't understand 'current on demand'....for what ? and what is the objective difference ?.
You said
I don't believe the major difference between the two topologies is about the slew rates, As most of the modern OPAs are fast enough, but their compressive VS expansive behaviors.
You state 'major difference' of what ?....objective or subjective difference.
This is not challenge I wish to learn what you mean, your take/description of subjective qualities is fine with me, with objective qualities even better.
 
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