John Curl's Blowtorch preamplifier part II - Page 3411 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd February 2013, 08:02 AM   #34101
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Quote:
Originally Posted by john curl View Post
Well, at one point I just said, let's test the JC-2 (we had a Crown IMA and a B&K wave analyzer in our lab). DON'T TOUCH THE SETTINGS. And I hand carried it to the test bench and found LOTS of higher order distortion. Yet, when I moved the pot, one way or another, the distortion dropped to the residual of the equipment.
There's the big clue ... what happened is that the movable contact surfaces inside the pot were refreshed, which made the distortion "go away". I've done this thousands of times with pots, give them a jiggle, to "clean" the critical surfaces, which instantly "fixes" the sound, and then listened to the sound steadily degrade over a period of time. It was good training for my hearing at the time, learning to recognise the signature of a typical pot which is both quality, and time dependent. It's no good trying to get a reading of a pot's distortion if you give it a twiddle to get the right setting immediately prior to taking a reading, you'll get a "perfect" result every time. How it needs to be done is to adjust the pot to some setting, and then run a musical signal through it for some minutes, up to hours depending upon the quality of the unit, then take the distortion reading without physical disturbing the pot in any way. In other words, there's what some might call a memory effect occurring here ...

Frank
  Reply With Quote
Old 3rd February 2013, 08:27 AM   #34102
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by john curl View Post
I don't need any stinkin' measurements to verify what my ears hear. What test equipment do you use today, kgrlee? Any?
That's below the belt JC. You know I'm a real beach bum.

But in da previous millenium, I spent a lot of time doing Double Blind Listening Tests and trying to correlate measurements to these Listening Test results.

I note JC's ears are so sensitive, that he can pronounce on sound quality without even listening to stuff. The price tag and labels on ICs etc are sufficient for JC's Golden er.rh 'Pinnae'.

It's a pity, he won't let such sensitive tools be used as part of a true golden pinnae Listening Panel.

I'm also confused, JC. Are you now spurning Hirata, Quan, 1ppzillion 7th harm distortion tests? I seem to remember you pontificating at length on these tests and dissing some true gurus for not understanding or carrying out these tests.

Are you saying you didn't carry out ANY tests on Blowtorch? Even Hirata, Quan & 7th harm. which you touted ad nauseum as important?

Or is it simply that your test results must NEVER be viewed by us Unwashed Masses who are incapable of interpreting them properly.
  Reply With Quote
Old 3rd February 2013, 09:05 AM   #34103
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
I am sure that a PLENTY of comparative listening tests had been performed ...
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 3rd February 2013, 09:18 AM   #34104
diyAudio Member
 
Join Date: Jan 2007
Quote:
Originally Posted by kgrlee View Post
Actually its JC who doesn't care about measurements ... even measurements that he's at pains to tell us ad nauseum, are important like Hirata, Quan & even simple THD & 7th harm.

I'm pleased to see that in Jurassic times, JC actually did measure things but this millenium, he's got out of the habit. And when he does measure things, they are certainly not for the consumption of us Unwashed Masses.

Pavel, on the other hand, has posted many measurements to support his views. Maybe, in the next millenium, JC will do likewise.
JC's stance is pretty clear and consistent.
We can agree or disagree with his modus operandi but he is certainly successful in what he does.
I, for one, am not part of his clientèle and will never be, but he (and the HiEnd industry in general) seem to be doing alright and can certainly afford to ignore "technocratic pr1cks" like myself.
Anyway, there are options for everyone and we can all be happy with our gear (or whatever gear is the flavor of the month, for those loyal to the "HiEnd camp").

On the other hand, it's disappointing to see people who are (supposedly) on the "objective camp" and with whom I generally agree, "turning John Curl" on us when certain chords are struck (Class D amps, for example).
__________________
"You have a hierarchy: a mathematician, a physicist (which is a failed mathematician), and an engineer (which is a failed physicist)." - Andrew Jones
  Reply With Quote
Old 3rd February 2013, 09:36 AM   #34105
gpapag is offline gpapag  Greece
diyAudio Member
 
gpapag's Avatar
 
Join Date: Nov 2002
Location: Athens-Greece
Quote:
Originally Posted by Esperado View Post
Gpapag, what do you think of this enclosure's group delay:
http://www.moonaudio.fr/Photos%20tai...up%20delay.jpg
Christophe
I can only say that it surpasses the “Blauert criterion” for an on axis measurement. (and that I would be proud if I could achieve such a measurement on a speaker of mine!)

Alas, in my opinion this criterion runs the risk of becoming a new “THD figure” case (for the speaker industry).

My understanding after careful reading Blauert-Laws paper is that there are more than one reason that this criterion –as stems out from that paper- is immature for to be adopted as a well tested GD figure of merit.

The complexity of the subject, the startling differences between theoretical predictions and actual measurements, as well as the painful result discrepancies from using artificial signals and musical signals for evaluating x-overs/speakers, are summarized in this exemplary work, which sites and discusses almost everything that has been tried so far
http://lib.tkk.fi/Dipl/2008/urn011933.pdf

George
Attached Images
File Type: jpg GD 1.JPG (147.3 KB, 175 views)
__________________
["Second Law is a bitch." - SY] ["The Road To Heaven:Specify the performance & accept the design. The Road To Hell:Specify the design & accept the performance"-Bruno Putzeys]

Last edited by gpapag; 3rd February 2013 at 09:41 AM.
  Reply With Quote
Old 3rd February 2013, 09:45 AM   #34106
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by PMA View Post
I am sure that a PLENTY of comparative listening tests had been performed ...
JC does- not even evaluate PGAs, despite they are cheap and ready to try with few mods:
eBay | NEW Version LCD PGA2311 Volume Remote Controller + Memory Save and Custom Texts

I ask myself what would be the interest to hire JC's efforts if nothing innovative never comes out. "I use what i know WORKS".
At Least, Mr Pass pretend he has provided his own solution to this interesting volume control question.
One of the solutions i could imagine would be to vary the DC voltages of the power FETS of a class D amp in order to tune the Level. And i have an other one to explore.

John provided a little Polaroid : " It appears that many people do not know how audio designers, like me, do their job."
I'm sorry, but when i was involved with audio design, we where 50% of the time exploring, imagining new solutions, sharing ideas etc. Under the acronym "R&D" is the word "Research".
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 3rd February 2013 at 10:10 AM.
  Reply With Quote
Old 3rd February 2013, 09:57 AM   #34107
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
Quote:
Originally Posted by gpapag View Post
Christophe
I can only say that it surpasses the “Blauert criterion” for an on axis measurement.
Notice it is a DIY collaborative project. systme triamplifi miniMaX
I wonder how much overpriced/poor sounding so calling "high end" loudspeakers (like Wilson Audio ?) could even approch this kind of results.
THIS kind of work *is* audio design, not arguing endless about resistance's sound.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 3rd February 2013 at 10:00 AM.
  Reply With Quote
Old 3rd February 2013, 10:16 AM   #34108
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Fas42, while your opinions are useful, it is NOT what I was measuring with the Waters precision pots that were originally the potentiometer in the LMP-2 and JC-2. There were DISTINCT defects in the coating that when the pot was set in a specific position, would add significant distortion. No amount of wiping helped the problem.
ALLEN BRADLEY square bodied pots had a different problem. They produced second harmonic over a wide range of operation. A completely different distortion mechanism.

Now when it comes to R&D: NO, I wrote my papers over 30 years ago. I did my time doing original research. That doesn't mean that I don't have a dozen or more remote controls in my living room, and I suffer through with their sound quality, marginal as it is.
  Reply With Quote
Old 3rd February 2013, 10:55 AM   #34109
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
That's interesting to know. Obviously the quality of manufacture is absolutely crucial to having a pot perform acceptably; every time I've been able to more thoroughly explore the audible behaviour of them I've always heard the characteristic I mentioned above, but none of them would have been of the top quality level you have been exposed to. Are there any papers or other writings which document the sort of behaviours you just mentioned, per brand and model?

Thanks,
Frank
  Reply With Quote
Old 3rd February 2013, 11:16 AM   #34110
diyAudio Member
 
Esperado's Avatar
 
Join Date: Jul 2011
Location: France
All the potentiometers, or adjustable resistances, suffer from contact's problem with time (with associated distortion and noise) even with the most prestigious of them (Penny & Gilles). No one wear in a nice way, even if you do not move them. Remember those adjustable in Revox whose cursor fell all alone due to oxidation.
The reason why i'm looking so hard about solid state solutions is the number of bottles of spray cleaner i had emptied in my life followed by a quick replacement..
If i'm satisfied with PGAs or similar, it is because , even if some found marginal losses in sound quality, they are clear winners after little time.
Now, the interesting question remains: how to improve them.
__________________
Ultimate Protection and more.The Only Source of Knowledge is experience, everything else is just information” ©A. Einstein

Last edited by Esperado; 3rd February 2013 at 11:19 AM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 11:35 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2