John Curl's Blowtorch preamplifier part II - Page 597 - diyAudio
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Old 13th September 2010, 09:15 PM   #5961
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This is where I depart from the papers I really worked on and therefore know pretty well, but in summary, if you look at Walt Jung's SID series, independently developed by 3 engineers, you will see how we can use THD to double check for TIM, even if the numbers might be slightly different. By 1980, we came to an agreement that 5V/us for preamps and 50V/us for power amps, given that there is no input stage 'dead zone' pretty much met the TIM measurement requirement. However, it didn't meant that op amps with more than 5V/us sounded as good as other designs. That brought up another challenge: WHY?
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Old 14th September 2010, 05:07 AM   #5962
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Neither high slew rate, nor any SINGLE parameter is able to assure good sounding crcuit.
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Old 17th September 2010, 02:34 AM   #5963
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Duh, pma! ;-)
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Old 17th September 2010, 03:05 AM   #5964
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PMA.

What are you trying to say............ you seem to be contradicting yourself.
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Old 17th September 2010, 05:17 PM   #5965
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Actually re-reading the question, days after I first posed it, apparently PMA was correct in his answer. Sorry PMA, my computer crashed days ago, and I forgot that I had asked that specific question.
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Old 17th September 2010, 05:29 PM   #5966
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Now, that we had cracked the slew rate barrier with the 5534 and the TLO-72, why didn't these devices supplant all previous audio designs for studio boards, phono stages, and consumer preamps? Well, people tried to use these devices to make world beatingpreamps, but they still fell short, somehow. And back to the drawing board.
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Old 17th September 2010, 05:34 PM   #5967
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John,

glad to hear your computer has recovered.

I would try these items:

- reasonably low distortion with high order harmonics as low as possible
- high slew rate
- very low noise
- input devices imune to EMI/RFI, thus JFETs
- hi idle current of output stage (and VAS)
- hi OLG -3dB corner
- low or moderate FB

?

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Old 17th September 2010, 06:45 PM   #5968
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Quote:
Originally Posted by PMA View Post
I would try these items:

- reasonably low distortion with high order harmonics as low as possible
- high slew rate
- very low noise
- input devices imune to EMI/RFI, thus JFETs
Or transformers.

se
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Old 17th September 2010, 08:32 PM   #5969
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Back in 1978, and into the mid-1980's, most serious designers stayed with discrete op amps or vacuum tubes, but we went in another direction for audio improvement. Even Dean Jensen, founder of Jensen transformers, made his own discrete op amp module. We just could not get the IC's to do it as good, not that we didn't try. In that time, a few papers came out that gave us further insight. Most are lost in obscurity at the moment for a number of reasons. In any case, we stayed with discrete designs, and looked especially at better passive parts and materials. Circuit board material came under criticism, and the term 'circuit board hook' had been invented by Tektronix, for DA in circuit board material. Dick Marsh, then working at LBL, tested caps and found them full of DA, for the most part. Walt Jung and Scott Wurcer found a NEW way to test for cap DA. We started extended measurements of every cap that we could find, and got results. More later.
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Old 18th September 2010, 12:59 AM   #5970
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Considering the given DUT, only look at transient information under complex harmonic loading as compared to a specifically designed complex input signal. the ear really only cares about the complex harmonic transient information in a real world signal, and really doesn't hear much of anything else, so simply test for what the ear is actually listening to. This would be a simple case of fitting the correct question to a fundamentally workable answer. I've already said this exact same thing in this thread and the earlier incarnation twice before this.

Why this simple and obvious point never seems to be heard is beyond me.

The point is that under the mathematical weighting of standardize testing regimes..this mentioned information amounts to something notably less than 10% of the 'entire signal' Thus, distortions tend to be in the 0.1% or less.

However, the ear only using those signal components..may see that 0.1% as seemingly like 10% distortion. Thus the need for proper weighting and proper analysis signals being in the chain. Test in the way that the ear listens, not to the way that engineers want to press buttons and/or use math...and see the world. See the world, or in this case, the ear -- for what it is.

These are vital and valid points.

Last edited by KBK; 18th September 2010 at 01:04 AM.
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