John Curl's Blowtorch preamplifier part II - Page 3353 - diyAudio
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Old 25th January 2013, 06:09 AM   #33521
PMA is offline PMA  Europe
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Quote:
Originally Posted by Steve Eddy View Post
Because a guru who says "I do not know" soon loses his followers. And what's a guru without followers?

se
Wise man, hopefully
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Old 25th January 2013, 06:25 AM   #33522
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Quote:
Originally Posted by ticknpop View Post
... I much prefer listening to my home built version of the Blowtorch, ...
Why didn't I think of this earlier!

Tick, how close to Blowtorch is your DIY version? JC published a schematic earlier.

Would you be prepared to lend it to eg Pavel or some true guru with the facilities to test it?

We could settle this "Blowtorch has high Hirata/Quan/7th harmonic dist." issue once & for all.

JC, would you lend someone your Hirata test box? I understand you might be reluctant to lend a $20,000 Blowtorch out but surely the Hirata box is OK ... especially as it doesn't seem you use it.

Hmmm! How do we make sure JC can't say Tick's box is cr*p if the test results aren't supa dupa?

JC, would you be prepared to "lay your hands" on Tick's blowtorch? ie check it out and listen to it to establish if it has all the unique goodness you designed into the original?

Or perhaps nominate a Blowtorch owner who's ears you trust to check it out on your behalf. But this wouldn't have the authority of a "laying of hands" by JC.
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Quote:
Originally Posted by ticknpop
If you have something positive to contribute besides your insulting, cave man / beach bum diatribes I'm sure we'd all like to hear them
Surely establishing good sound (pun intended) reasons for the failure of JC2 Mk1 ... that aren't mythical "all OPAs including AD797 are evil" is constructive?

I've suggested several measures to avoid such fails in future which some gurus here agree with. eg read the f**king datasheet. This might be of use to someone attempting to design or build something similar in future.
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Old 25th January 2013, 11:42 AM   #33523
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by Max Headroom View Post

I have placed a standard clay house brick on top of my cd player in the past and the added mass altered the sound. Rotating the brick 180* further altered the sound

Dan.
Dan
I won’t touch any driver or tube today (I am still under the influence of the full moon) so I can -relatively safely- respond to this.

Pour sand on a bag, catering for the same mass and footprint as the brick you used.
Place this bag on top of this CD. Listen. Then rotate the bag 180d. Listen again.

Quote:
I have noted sonic changes by…
For me, the acoustic tests is the start and the end. In between, I have to do some measurements to record subjective data in order to see if I am running after some ghost.

I will post a totally humiliating personal experience.

Some 3 years ago I started work on a three driver OB speaker.
The first passive x-over was build with what I had available.
After roughly trimming the acoustic levels of the drivers by using resistors, I spend some two hours trying to decide by listening on the relative polarity btn mid and high drivers. Back and forth several times, I was quite certain in the end that a certain polarity relation was acoustically better.
After that, I went to do some measurements. As I was setting up the jig, I approached the input of the x-over to do the connections.
There, I saw that the + of the tweeter’s wire was disconnected from the x-over output.

All the listening and decision making based on my careful noting of sonic changes was done with the tweeter disconnected. Oh well FLEETWOOD MAC - Oh Well (1969 UK TV Performance) ~ HIGH QUALITY HQ ~ - YouTube

George

PS. Nothing is safe. Too late! The smell informed me that while typing, I burned the food in the kitchen.
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Old 25th January 2013, 12:05 PM   #33524
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kgrlee, looking at the schematics, i believe there is NOTHING to be blamed about quality of the blowtorch (if devices are correctly matched, PSU good enough with no ground loop issues, and charge not in excess).
Schematic is healthy, no feed back, so no induced TIM, and if their distortions measure well, they, for sure will sound good. Nothing mysterious, exceptional or revolutionary as well.

We can disagree about the way John is always pretending to be the best of the universe, or the outrageous price of some of his products, or smile about the 'legend' around, or the john 'audiophile' and sometimes arrogant attitude, but this does not affect its engineering's qualities, on my point of view.

You can debate about some of its position, about mysterious cables, handcrafted by virgins witch are the 'only ones' etc. where audiophile marketing take the place of the correct scientific approach, but did he deserve this hate turning in circles ?

Yes, we are allowed to say that other ways can lead to good sounding products (may-be better ?) , like the use of good and wise chosen OPAs, and in a more general way, good use of feedback loops, but that does not imply that the John's choices are bad.

Give-you a favor, please, bring your inputs in a positive way, you begin to deserve-yourself with this litany, more than John with some of his broad, sweeping statements.
A pity, for me, as i take-you too for a valuable engineer.
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Last edited by Esperado; 25th January 2013 at 12:10 PM.
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Old 25th January 2013, 12:43 PM   #33525
SY is offline SY  United States
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Christophe, my attitude exactly. I'll take shots at the horse chips John likes to fling around, but when the rubber met the road, I recommended his power amps for my boss to buy (he likes the performance a lot, he hates the lousy XLR connectors they use).

The BT is most likely just as audibly transparent as any other good preamp despite the voodoo atmosphere that John likes to create around it.
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Old 25th January 2013, 12:52 PM   #33526
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Quote:
Originally Posted by Max Headroom View Post
Perhaps others here could explain permanent magnetic fields influencing the behaviour of steel enclosures further to the information already given in recent posts.
Dan.
That's very easy. The magnet is forcing the steel to move along it's hysteresis curve. As a result, the small signal permeability the low level magnetic fields of the wire sees gets lower.

Good magnetic irons really lose permeability in the 1.5 to 2 tesla range, and when they do, they begin to lose field containment and more of the magnetic field goes beyond the iron. 1.5 to 2 tesla is actually not that hard for the Neo magnets at their surfaces. You need a lot of them if you wish that kind of field present in a reasonable air gap, that's a lot of magnetic energy.

Quote:
Originally Posted by fas42 View Post
and explain all of this in everyday, fully comprehensible language ...Frank
Well, that leaves me out...

jn

ps..I did find this interesting article on arc welding lorentze force measurement. They shield the linear displacement transducer from the arc electrical noise by alternating copper foil and mu metal, mentioned in para 3.. IIRC, somebody on this very thread mentioning that..

http://eagar.mit.edu/EagarPapers/Eagar031.pdf

Last edited by jneutron; 25th January 2013 at 01:02 PM.
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Old 25th January 2013, 12:58 PM   #33527
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Quote:
Originally Posted by PMA View Post
It is fine with me that we have audible differences. Not fine are the pseudo-engineering and pseudo-scientific attempts to explain the differences. Why not better just to say "I do not know?"
And not only that, it was such an easily testable claim ... why not, you know, test it!
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Old 25th January 2013, 01:03 PM   #33528
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Default Not Possible...Not Invented Here....

Quote:
Originally Posted by john curl View Post
Max, it is difficult to discuss audio differences here, because of the criticism. It is best to let it go.
Hi John, yes I respectfully take that as good advice.
In the observational cases I have described, I am sincerely asking for physics explanations from the theory adept fellows collected here....oh well....

Dan.
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Old 25th January 2013, 01:17 PM   #33529
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Originally Posted by Max Headroom View Post
Hi John, yes I respectfully take that as good advice.
In the observational cases I have described, I am sincerely asking for physics explanations from the theory adept fellows collected here....oh well....

Dan.
Um, look up two posts.
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Old 25th January 2013, 01:28 PM   #33530
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Quote:
Pour sand on a bag, catering for the same mass and footprint as the brick you used. Place this bag on top of this CD. Listen. Then rotate the bag 180d. Listen again.
Typical clean sand has no permanently magnetisable iron content, however sandbags can be a good mechanical damping method.

Quote:
For me, the acoustic tests is the start and the end. In between, I have to do some measurements to record subjective data in order to see if I am running after some ghost.
Enough A/B comparisons and even very fine effects are reliably discernable. Measurement will of course confirm this....provided that the correct testing methodology is performed. Diffmaker can be your friend in cases where standard steady state testing is not easily revealing.

Quote:
......After roughly trimming the acoustic levels of the drivers by using resistors, I spend some two hours trying to decide by listening on the relative polarity btn mid and high drivers. Back and forth several times, I was quite certain in the end that a certain polarity relation was acoustically better.
After that, I went to do some measurements. As I was setting up the jig, I approached the input of the x-over to do the connections. There, I saw that the + of the tweeter’s wire was disconnected from the x-over output.
All the listening and decision making based on my careful noting of sonic changes was done with the tweeter disconnected.
So you were hearing changes according to the polarity of only the mid driver then ?....if so, then there is nothing to be embarrassed about. Not noting the missing highs is another matter .

Quote:
PS. Nothing is safe. Too late! The smell informed me that while typing, I burned the food in the kitchen.
Best you stay in bed then....put your mattress on the floor and don't move .

Dan.
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