John Curl's Blowtorch preamplifier

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#17,441
I believe in Barrie Gilbert's research in op amp design. Barrie himself is quite a difficult person to work with. I first met him 35 years ago, at an ISSCC convention in 1974. I met Walt Jung the same day. Barrie thought that TIM was 'crazy', at the time, at least with my verbal explanation of the problem. Years later, he proved it true, in print. What is interesting, was that it took years for Barrie to take it seriously. Typical of the type.
Remember:
It doesn't exist.
It exists, but it is not important.
We invented it.
Sometimes, I don't know whether we should laugh, or cry, or silently cheer: 'Finally!'
 
#17,442
john curl said:
What is interesting, was that it took years for Barrie to take it seriously. Typical of the type.
Remember:
It doesn't exist.
It exists, but it is not important.
We invented it.
Sometimes, I don't know whether we should laugh, or cry, or silently cheer: 'Finally!'
Click to expand...

Barrie somewhat regrets the conclusions that people have extrapolated from his article. If you bother to read it carefully he uses exaggerated numbers in some cases to make a point. One case is unity gain BW of 100X max signal of interest. This translates into 2MHz for audio. Yes, circa 1969 op-amps, meaningless today unless one clings needlessly to the idea that nothing has changed in 40yr. Sound familiar.

And please stop with the TIM already. As a manifestation of full power bandwith it was written about in the 60's. As professionals the audio community has cultivated a culture of ignoring much of what goes on in the rest of the engineering community.
 
#17,443
john curl said:
I believe in Barrie Gilbert's research in op amp design. Barrie himself is quite a difficult person to work with. I first met him 35 years ago, at an ISSCC convention in 1974. I met Walt Jung the same day. Barrie thought that TIM was 'crazy', at the time, at least with my verbal explanation of the problem. Years later, he proved it true, in print. What is interesting, was that it took years for Barrie to take it seriously. Typical of the type.
Remember:
It doesn't exist.
It exists, but it is not important.
We invented it.
Sometimes, I don't know whether we should laugh, or cry, or silently cheer: 'Finally!'
Click to expand...


I gather it then that you rather would accept something based on authority, tradition or religion instead of keeping on asking hard questions?

Jan Didden
 
#17,445
Scott, please, either learn and grow, or leave it alone. TIM is only an early manifestation of the problems with op amp based amps. Still, it took Barrie and many others, many years to incorporate it into his writings. PIM is what we are mostly concerned about today.
Now, Scott, let me tell you straight:
I am now using your AD797 in the front end of my ST 1700B analyzer, and I suspect it is giving me some residual 7th harmonic distortion. When I changed analyzers WITHOUT your AD797 op amps incorporated, the 7th harmonic has disappeared. Looks suspicious.
Still, I designed your AD797 in a new phono stage that Parasound will be releasing shortly. I needed something that could be made by others in a relatively small package. Objectively, I evaluated the competing Op amps and decided on your unit, because of low noise and low measured distortion. I still have the option of making your output stage class A, and I probably will do so, no thanks to any input from you on optimizing this.
This will be the best that I can do with analog IC's, but my discrete Vendetta phono design will be better in every way, except measured distortion, as I have decided to run the entire design, open loop. I still have to compete subjectively with Charles Hansen and Nelson Pass. I trust their approach over yours.
Barrie, perhaps inadvertently, gave us OBJECTIVE hope that we are on the right track with PIM.
Of course, his model is made to bring out the distortion, BUT it is also too ideal in many other ways, so that he could hone in on one SPECIFIC distortion mechanism.
We are at phase 2: It exists, but it is not important.
 
#17,446
john curl said:
Scott, please, either learn and grow, or leave it alone. TIM is only an early manifestation of the problems with op amp based amps. Still, it took Barrie and many others, many years to incorporate it into his writings. PIM is what we are mostly concerned about today.
Now, Scott, let me tell you straight:
I am now using your AD797 in the front end of my ST 1700B analyzer, and I suspect it is giving me some residual 7th harmonic distortion. When I changed analyzers WITHOUT your AD797 op amps incorporated, the 7th harmonic has disappeared. Looks suspicious.
Still, I designed your AD797 in a new phono stage that Parasound will be releasing shortly. I needed something that could be made by others in a relatively small package. Objectively, I evaluated the competing Op amps and decided on your unit, because of low noise and low measured distortion. I still have the option of making your output stage class A, and I probably will do so, no thanks to any input from you on optimizing this.
This will be the best that I can do with analog IC's, but my discrete Vendetta phono design will be better in every way, except measured distortion, as I have decided to run the entire design, open loop. I still have to compete subjectively with Charles Hansen and Nelson Pass. I trust their approach over yours.
Barrie, perhaps inadvertently, gave us OBJECTIVE hope that we are on the right track with PIM.
Of course, his model is made to bring out the distortion, BUT it is also too ideal in many other ways, so that he could hone in on one SPECIFIC distortion mechanism.
We are at phase 2: It exists, but it is not important.
Click to expand...

Obviously, you could use some help. What about the physics and electronics engineering graduated, microwave IC's maker, former Agilent engineer and current Bybee associate?
 
#17,451
john curl said:
Don't attempt to put words in my mouth, Jan. I'll give you a piece of my mind that I was reserving for Traderbam, if you don't cease and desist. I don't have to answer such a confining question.[snip]
Click to expand...


Well, I asked a question about how you decide to accept something. Remember, related to Barrie's quote: "Keep asking the hard questions" (paraphrased). I asked if you do that as well (and by inference would accept it from us) or whether you would accept something based on authority, tradition or religion (edit: and would expect that from us).

Edit: this post: http://www.diyaudio.com/forums/showthread.php?postid=1803055#post1803055

Since you didn't answer, I assumed the possibility which I have seen you use here, namely that it would be based on authority, tradition or religion (although I'm not sure about the religion part).

If I'm wrong let me know, if my question was NOMB tell me its NOMB.

john curl said:
[snip]When did you last beat your wife, Jan?
Click to expand...


Which one?

Jan Didden
 
#17,452
That is as DUMB as my question about you beating your wife. I LISTEN, also I have a degree in physics, and have taken a significant number undergraduate and graduate courses in electronic engineering. I hire PhD's on occasion for special problems and have done so for the last 35 years. I don't have to rely on any authority, except my personal experience, which is extensive.
 
#17,457
Bumped into this book today and thought I'd share info with those interested. May have been mentioned here already, but you never know.

Title: The Sound of Silence (Lowest-Noise RIAA Phono: Amps Designer's Guide.)
Author: Burkhard Vogel
ISBN: 978-3-540-76883-8

Anyway, happy reading.

Franklin
 

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