John Curl's Blowtorch preamplifier part II - Page 3336 - diyAudio
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Old 22nd January 2013, 07:54 PM   #33351
gk7 is offline gk7
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Probably this one: The Bastard Operator From Hell Complete
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Old 22nd January 2013, 08:17 PM   #33352
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John and others; a question about IC's. Like a number of readers (rather than participants) in this thread I am out of my depth with the more technical issues but like the idea of gaining insights so as to modify my own system. You have mentioned the AD825 favorably a couple of times. My question concerns "settling time". About 40 yrs ago Gordon King and JLH in the UK were advocating a low settling time as an important criteria for a good subject response from power amps.
I notice the AD825 DOES have a very low settling time compared to a lot of other IC op'amps.
Has anyone got any thoughts on this as an indication of good subjective sound......?
And if so why.........?
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Old 22nd January 2013, 08:41 PM   #33353
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My criteria is: Fet input, wide open loop bandwidth.
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Old 22nd January 2013, 08:49 PM   #33354
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Quote:
Originally Posted by jneutron View Post
Answers.
jn
Thanks for going into the trouble jn
Still in the dark but itís not because of you.


Quote:
Originally Posted by PMA View Post
If there is anyone interested, here is the complete measurement of opamps + schematics.
Thanks for sharing Pavel.
What is the output level in these measurements and on what load?

Any 5532/5534 on your bench?

George
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Old 22nd January 2013, 08:52 PM   #33355
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ED Re; graph #33343.
Is it some sort of inverse F-Munson curve?
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Old 22nd January 2013, 08:53 PM   #33356
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Originally Posted by Jonathan Bright View Post
ED Re; graph #33343.
Is it some sort of inverse F-Munson curve?
Bingo! Yes it is. Or a curve of the ear's sensitivity.
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Old 22nd January 2013, 08:54 PM   #33357
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Originally Posted by simon7000 View Post
"0.55 pV/Hz1/2, more than
three orders of magnitude lower than would be possible with
the best conventional room-temperature voltage amplifier."

Great, now we gotta do all our recordings in a giant dewar flask.
Not the point, I assume the experimenters were at room temperature. They were able to build an experiment that had <-200dB line contamination, in fact .55pV is almost -246dBV!
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Old 22nd January 2013, 08:54 PM   #33358
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George, as already mentioned, output voltage is close to 1Vrms. As shown in the schematics in the document, load is 1k (FB 1k + 10 ohm).
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Old 22nd January 2013, 09:08 PM   #33359
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Originally Posted by john curl View Post
Please give it a break, PMA. 7th harmonic is STILL very important. I challenge YOU to make something better than my designs, rather than 'bad rap' me.
JC, how about measuring or letting someone measure Blowtorch to see how much 7th it has under comparable conditions to AD797 etc. I'm sure Pavel will be happy to do so.

Much more convincing than 'pontificating on your 'calculations'. Have you checked your calculations against Baxandall? He actually measures stuff to confirm his measurements of exactly this effect.

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Then I mentioned that I was still thinking of building a solid state 'transformer eliminator' and they 'showed me the door' literally, claiming that their best engineers had claimed it impossible, and therefore I was just some 'nut' wasting their time. ... I had the problem solved in 1968, ... follow the input stage with something elegant, rather than just an add-on circuit. ... Ultimately the Levinson JC-1 appeared with a rated noise of 0.4nV/rt Hz noise at the NY AES in 1973. ... Low noise design has been known about (what to do) for many decades. The problems are: .... If you can do all three, you have a good chance of making a low noise, successful audio design.
Would you like to tell us how with all this supa dupa experience & superior knowledge, you ended up with the original JC2 Mk1 circuit that was caned by the reviewers?

Last edited by kgrlee; 22nd January 2013 at 09:12 PM.
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Old 22nd January 2013, 09:13 PM   #33360
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Originally Posted by scott wurcer View Post
Not the point, I assume the experimenters were at room temperature. They were able to build an experiment that had <-200dB line contamination, in fact .55pV is almost -246dBV!
But they weren't SY either.

I think way back I showed a -180 result of one of my toys.
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