John Curl's Blowtorch preamplifier part II - Page 2945 - diyAudio
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Old 17th November 2012, 11:00 PM   #29441
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Originally Posted by fas42 View Post
Also, I would be interested in comments from those expert in this field, on this situation: a multi-strand, say 256 strands, cable connects two points, and for whatever reason a single strand at one end goes, or is open circuit -- less than perfect soldering, metal fatigue from too much handling, whatever. Now, to me that looks like a pretty good RF antenna, which to some degree is shorted out by resting against other bits of copper. Depending on vibration, level of oxidising, and just about everything else you can think of.

Is there a definitive answer on what happens here?

Frank
Heaven forbid we talk about crimp connections. Once the wire touches the rest of the bundle the "openness" ceases, lets not talk about micro-diodes again.
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Last edited by scott wurcer; 17th November 2012 at 11:04 PM.
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Old 17th November 2012, 11:05 PM   #29442
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Originally Posted by gpapag View Post
Ref. Distortion measurement, perception and masking:
Alex. Voishvillo (now with JBL) ALMA 2009 Europe
http://www.almainternational.org/***...0acoustics.pdf

... from (p. 6-7):
http://publications.lib.chalmers.se/...ext/126969.pdf
I'm always excited when I hear of stuff done since I went bush but am invariably disappointed. Loads pontificating but where are the Listening Tests especially on speakers? Even pseudo prophet Floyd does little but confirm Peter Fryer's work from 70/80s.

When you start trying to confirm some of this with Listening Tests, you immediately come across unexpected stuff like, "dis dun sound like speaker distortion at all" or "why is does dis with low measured distortion 'sound' more distorted to the Listening Panel" and "All dem self declared Golden Pinnae are deaf !" If you don't do Listening Tests, you start chasing unimportant stuff while the really audible stuff is staring you in the face.

A Listening Test is a measurement. Your instrument is your Listening Panel. The instrument has an accuracy which needs checking and calibration every now & then.

I don't buy "JC Maxwell (or Washington or other famous name) says it has Unobtainium and is made by virgins so it must be good."
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The conclusion I have a hard time with... to use the knowledge to sort of hide and cover up the poor driver performance. I guess if you have taken the dynamic driver technology as far as you can and its still pretty bad, you can use this approach.
There are good reasons why Rice & Kellog's invention is still dominant after nearly a century.

I'll put up certain moving coil speakers against any other technology to win by a wide margin on music in a properly conducted Blind Listening Test. Yes, it distorts but in less important areas than any other technology.

For it's remaining distortions, I'm really a speaker man. I've chased 1ppzillion THD in amps but to me, an amplifier is just a crossover component so I begrudge anything in a power amp if doesn't improve amp/speaker. eg an extra stage may reduce THD from 0.01% to 0.001% but often makes the amp more susceptible to instability with certain speakers. Many (all?) Golden Pinnae amps are guilty of this.

Mr. Curl, which Levinson 1980's power amps were you involved with ?

I posted this in another forum.

>For what it is worth, I think this is impossible. It seems to violate the cause and effect principle. How could the amplifier "know" what the speaker is up to? Short of sensing the actual motion of the drivers or the actual sound... this has to be sort of by guess and by golly, it seems to me.

It is entirely possible for an "amplifier" to know what the speaker is doing.

It needs to sense the speaker current. An amp which twiddled its Output Z using both current & voltage feedback does this. Speakers act as accurate microphones (sense the actual sound) if operated into Low Z.

See "Loudspeakers as Microphones" - Peter Baxandall special lecture London AES (early 80s, late 70s?)

If operated into High Z, then the voltage at the terminals is a measure of cone velocity.

Both these mechanisms obey superposition & Thevenin so if you're clever, you can look at this while the amp is giving zillion volts and amps to the speaker. But non est tantum facile.

There are several tried & tested methods of using this "controlled output Z" or "current + voltage feedback" or "actual sound & motion feedback" (different descriptions of the same thing) if you incorporate the amplifier design in the speaker. Some of these are in the zanier incarnations of my Powered Integrated Super Sub technology.

The simplest is the negative output R that Fons mentions.

More sophisticated but similar (??!) is ACE technology by Erik Stahl which was used by Audio Pro, Sweden for subs. Unfortunately, since he left, there isn't anyone there who understands it. Anyone have a contact for Erik? Or a clean copy of his original AES preprint?

These methods have the distortion reduction and dynamic overload protection features discussed in Mills & Hawksford. However, they are badly affected by heating of the voice coil.

David Birt did an excellent IoA paper at Windermere where he arranged speaker and amp in a bridge so he could measure and compensate for heating on the fly. Anyone have an email for him?

These are the most elegant methods and they can be analysed from many viewpoints. Some of these viewpoints don't show up the distortion reduction advantages clearly.

I'm contemptous of methods which rely on extra transducers or extra windings (like Mills) or zillion point DSP EQ especially if they don't give ALL the advantages of the elegant methods.

A brute force zillion point approach possible today is measure accurately speaker Z (not that easy) and tailor the output of a High Z amp to suit. This would give some but not all the advantages of the above systems cos it wouldn't "know" what the speaker is up to.
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Old 17th November 2012, 11:39 PM   #29443
fas42 is offline fas42  Australia
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Originally Posted by scott wurcer View Post
Heaven forbid we talk about crimp connections. Once the wire touches the rest of the bundle the "openness" ceases, lets not talk about micro-diodes again.
Meaning that micro-diodes don't exist, or are irrelevant, can't have any audible effect if they do exist?

And, if two pieces of metal touch, we then have a perfect connection, can be modelled in Spice as a straight line? I do note that there are such devices as metal oxide - metal diodes, used for doing real things ...

Frank
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Old 17th November 2012, 11:50 PM   #29444
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Mr Curl has not stepped back in real-life hard confrontations.

He has proved that he has courage. Do a reading of his professional life.
Thanks for the warning George but I'm perfectly aware of JC's reputation though I have been out of circuit for more than a decade. I think the best summary is the reply he posted to Bob Cordell about how 'proved' zillion V/us and I second Bob's opinion in his reply.

I'm waiting to see if he bites and who he is offering for the Blind Listening Test panel. This is of considerable interest to me as my list of self declared Golden Pinnae who aren't deaf is very short; in fact empty after nearly 2 decades of conducting these tests.

You could also accuse me of making outrageous statements without having to bankroll the forfeit if the results go against me as I'm presently destitute ... and you'd be right

But seriously, what I'm trying to show is that it is possible to devise a Blind Listening Test that meets ALL the objections of the Golden Pinnae.

Persuading JC to participate, which is a considerable investment for him with no possible advantage & big -ve consequences possible is another matter. There's where the courage lies.

But if he bites, I'll have to see whether John Atkinson remembers a mad Chinaman. The Dynamic Duo already know rumours that I'd been eaten by a crocodile are false.

Anyone know of Blind Listening Tests which involved JC or his designs?

And Mr. Curl, I'd still like to know the 1980's Mark Levinson amplifiers you designed. Just to tidy a loose end from the previous millenium.
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Old 17th November 2012, 11:58 PM   #29445
jcx is offline jcx  United States
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missed Doug Self's measuring oxidized connectors? - including a rusty nail as I recall

read up on Ohmic contacts, tell us why in a cable the signal is "going thru" a non Ohmic junction when it has all these sub uOhm paths around
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Old 18th November 2012, 12:00 AM   #29446
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I would be interested in any studies that have attempted to understand "bad" connections, in reference to audio performance. People frequently cite gold to gold as doing a "good enough" job -- try telling that to an old PC I once had in a seaside environment, that started getting dodgy. Pulled it apart, and was impressed by the green muck coating the gold contacts everywhere. Of course, all gold coating used in audio gear is far superior, so we don't have any worries ...

Frank
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Old 18th November 2012, 12:06 AM   #29447
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Originally Posted by kgrlee View Post

Anyone know of Blind Listening Tests which involved JC or his designs?
John has talked about them repeatedly. He couldn't hear the wonderful things he could hear when peeking, so his excuse then was that the tests were flawed. His excuse now is that he's old and can't hear the things he could hear when he was younger, or at least not as quickly.
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Old 18th November 2012, 12:07 AM   #29448
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read up on Ohmic contacts, tell us why in a cable the signal is "going thru" a non Ohmic junction when it has all these sub uOhm paths around
I'm not worried about the signal itself, I'm worried about that faulty strand acting as an input for external interference. To take it to a "purer" level, consider the overall cable to be Litz, single broken strand at one end. Bring a strong RF source deliberately very close to the cable: will there or will there not be any pickup?

Frank
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Old 18th November 2012, 12:28 AM   #29449
RNMarsh is offline RNMarsh  United States
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Originally Posted by fas42 View Post
Also, I would be interested in comments from those expert in this field, on this situation: a multi-strand, say 256 strands, cable
Is there a definitive answer on what happens here?

Frank
I know that strands of copper will oxidize and thus create issues of strand-to-strand effects (weak diodes?). Its the main reason to go to oxygen free copper wire(s). That and the effects of the oxide (semi-conductor) on the surface travelling part of the signal - on skin depth signals. I dont know of the specific listening consequences of oxide but would rather avoid it, just in case -RNM

Last edited by RNMarsh; 18th November 2012 at 12:38 AM.
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Old 18th November 2012, 12:31 AM   #29450
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Originally Posted by john curl View Post
No double blind-tests for me, thanks.
So you prefer blind trust ?
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