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In Reply to: Re: That's what I was thinking.... posted by Mr. Morello on May 06, 2003 at 13:48:21:
Doug Self and I have been battling in print for the last 19 years. He, at first, thought that there was no significant difference between caps. We had one heck of an LTE dogfight back in '84-'85. He is not on this website. He is a high feedback kind of guy.
Actually, the most important thing seems to have as high as possible open-loop frequency response, before feedback. This seems to reduce FIM to acceptable levels. Higher order distortion is usually caused by a kink in the transfer function, like x-over distortion. It is a separate problem from hi vs low feedback.
Follow Ups:
I hope it was a friendly battle :-)
I'm a medium feedback boy. I run 60dB loop-gain in my preamp.
It sounds ultra-clean and exhibits very low noise.
I strive for high open-loop-bandwidh, fast slewrate and so on.
Have you done measurements on phase-modulation?
I belive that Barrie Gilbert wrote a nice article on the subject.
He did some simplifications, but it is still a excellent paper.
Barrie Gilbert's work is excellent, but Matti Otala firstgave a paper on the subject in the early '80's as a talk at the AES.
I dont know much about Matti. Barrie G appears to be talented.
Do you have any comments to The Halcro-amps?
Barrie Gilbert, is sharp--VERY SHARP--and I have learned from him, BUT Matti Otala was first with a really good paper. I am pretty sure that this one did NOT get in the AES Journal, because it was too far ahead of its time. When I first spoke to Barrie Gilbert about TIM at an ISSCC conference in 1974, he looked at me like I was crazy ! Well, I maybe I sounded crazy at the time, but I knew that this was important. Later, Walt Jung worked with Barrie at Analog Devices. Walt told me that Barrie could be very condecending and petty with other's intellectual efforts, and this forced a lot of rewriting. You will see swipes at Matti in Barrie's paper, and that is why I bring this up. It is a perfect example of: 1. It doesn't exist, 2. It exists, but it's not important 3. We invented it !
Halcro amps are VERY interesting, and they measure virtually perfectly. They appear to have local high feedback loops mostly using video ics.
Hello Curl,I have read Barries paper again. He refers to Otala:
"Predictably, Otala's 'discovery' only added welcome fuel to the fire of those who were quite convinced that these new-fangled transistor amplifiers were genetically incapable of pleasing the audiophile ear, a notion which, like all myths, persists unabated, in spite of the fact that the root cause of TIM is now completely understood, and can easily be avoided in transistor amplifiers expressly designed for the most demanding audio applications. Nevertheless, Mister Otala was on to something, and although there are many splendid op amps out there, not all deliver quite what the textbooks promise"
In my view, slewrate-induced distortion(due to clipping when driving the Ccomp at high f) and phase-modulation(due to the fact that the Ccomp is "magnified" by non-linear loopgain), can me reduced by a sharp designer. Barrie has a point when he says :"Otala's 'discovery' only added welcome fuel to the fire "
The problem associated with poor(low slewrate and high open-loop-THD) OP-amps such as 741 are rather obvious.\Morello
First of all, I am listening to Matti Otala's first amp in my lab. It still sounds great after its design, at Philips Research Labs about 30 years ago. It is all bipolar transistor for the active devices. I tend to use fets, if possible, but this little amp is great! Even today.
Matti Otala is a PhD professor, and not 'Mr. Otala' He may go by just Matti, but not Mr. Otala. This is a swipe.
"Matti Otala is a PhD professor, and not 'Mr. Otala' He may go by just Matti, but not Mr. Otala. This is a swipe. ":-) I didn't neglect "professor" intenionaly.
Yes, I know you are a JFET/MOSFET-man. I use JFET's(2SK170 and 2SK117) as input devices in preamps and RIAA-amps and 100% bipolar in poweramps. Do you know where I can find PhD PROFESSOR Matti Otalas paper that he published in th 70's?
I have the schematics to PhD PROFESSOR Matti Otala's beloved amp right in front me. It appears to be a VERY great design if one consider that it is that old.An other old amp that I like is the Krell KSA100. It's so simple, but at the same time somewhat elegant :-) And a LOT of feedback! :-D
It was not you, but Barrie Gilbert who made the insult.
ok\Morello
Mr. Morello, I hope that you understand that I was not directing anything at all personal to you. You were just quoting Barrie Gilbert. I just wanted to show a part of HIS personality that I find disturbing. Barrie knew better.
Hello Curl,I understand and I do agree.
regards\Morello
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