Lumba Ogir said:
Hi Lumba,
First of all, the lack of a detailed and coherent argument usually does not prevent anyone on this board from contributing - nor should it.
Your argument, while much more long-winded, was no more choerent and detailed than syn08's. Hand-waiving is hand-waiving, regardless of length and regarless of the use of quasi-technical jargon.
Cheers,
Bob
john curl said:
Maybe you do not know John but Dr. Otala is still alive. He currently teaches in Tampere, Finnland:
http://otala.com/pages/mao/
You can send him a mail on the mentioned mailadress ! When you do so please send him our regards.
Lumba Ogir said:
I did provide substance. The designer of that amp said that the "the sound improvement was staggering" when he increased feedback. So far, most posters in favor of Otala here have implied that the Otala amp was so good because it has low OLG (and thus relatively low FB factor).
So this proves that a) the Otala amp wasn't that great to begin with because it could be improved staggeringly, and b) that improvement came about by significantly raising (by 10dB) the feedback.
That's all I implied. I think the info supports that. If your view is different I'd like to know why.
Jan Didden
Otala's 'great research' could be improved upon 'stagggeringly' by adding 10dB of dreaded feedback....Lumba Ogir said:
Anyway, in Matti's defence, I think we should remember that he never presented that amp to the AES as 'the ultimate amp'. He presented it to illustrate design principles to minimize TIM. And it did minimize TIM.
What we learned later was that you could also minimize TIM and still have a very low distortion high feedback amp. So he did bring audio a step forward.
Jan Didden
janneman said:
This is what I did with this type topology, one can get extremely low distortion without much complexity, the THD20 slope is much reduced over a conventional 2 stage voltage amplification stage and not to mention hefty increase in slew rate. Quite low THD figures at even 50 Khz and even 70 Khz can be obtained this way.
This was the route taken by the top of the line Pioneer amps of the late 1980.
Not easy though, its hell to get stable when applying healthy dose of feedback but doable.
Take a look at George s research on the three stage voltage amp for more reference, http://www.geocities.com/ResearchTriangle/Node/2356/
Not really John, Ive managed to get my design sounding pretty close to my reference Nemo monoblocks, maybe you dont like what these sound like. In measuring THD20 the Nemos wont come close.
Actually, feedback through 3 stages is not to scary in reality how somebody may think about; the main point is, it should not be the single feedback loop.
Wavebourn,
I agree. A 3 stage amp with feedback can even be made without phase compensation. (You see, that`s a significant borderline to me).
Hi Jan,
It is my impression that you are typing under influence (of syn08). Do you remember discussion of Baxandall individual harmonic measurements vs loop gain? Do you remember that his calculations and measurements (and Cordell simulations) showed wave behavior for high order harmonics for loop gain from 0 to 40 dB? It is possible that with this extra 10 dB cause some compensation of high order harmonics (decrease more than 10dB).
From the other hand, I can find dozen of quotes for you "I lower feedback from 20 dB to 10 dB and "the sound improvement was staggering".
Please think for yourself. Don't speak too soon.
Thank you.
dimitri said:
Not sure I see this influence, but in general would it be a bad thing? Should I be proud or ashamed of?
Jan, next time do Dimitri a favor and type under the influence of (Joshua_G). You are going to make lots of people happy.
Dimitri: here's about where the Baxandall stuff started: http://www.diyaudio.com/forums/showthread.php?postid=1277808#post1277808
Please re-read that in context, you'll find out it has absolutely nothing to do with Otala, PIM or anything else in the current topic. BTW, if you can find a quote as you mentioned, based on anything but elusive "listening tests", I would appreciate a link.
Hi Ovidiu, I think you should be proud.
In his post Jan didn't mention PIM, he mentioned that extra 10dB of feedback is GOOD, based on the same "elusive "listening tests." 🙂
And please don't bite Joshua.
Peace
In his post Jan didn't mention PIM, he mentioned that extra 10dB of feedback is GOOD, based on the same "elusive "listening tests." 🙂
And please don't bite Joshua.
Peace
Lumba Ogir said:
Sure, if feedback loop does not meet the criterion of 180 degrees and more than unity gain on any frequency. That means, all stages must have different frequency characteristics. But the faster stage before the slower one will definitely clip first starting from some signal level starting from some frequency. Since they are all in the loop it does not matter is it an input stage, or is it an output stage. The obvious solution is to use a diode clipper before the slowest stage, even if it will be engaged with higher frequencies only. I don't know if a frequency dependent clipper as a countermeasure against severe distortions caused by slew rate limiting patented or not, but if it is not you may assume it in Public Domain as soon as I click the button and submit this post.
dimitri said:
Hello Dimitri,
Wow, lots of questions. OK, here goes.
1) Yes, yes and yes. I am well aware of the Baxandall stuff, and the variation of harmonic components with feedback magnitude. I brought it up here often. But the issue here is that the designer of the O-amp stated that the amp staggeringly improved when he added feedback. I have not claimed anything more. I don't know the exact cause. I do know that when they added that feedback, that was the version they marketed and that went on to be very successful. So to me that proves that the adagium 'feedback kills the sound' or similar statements are simply unsubstantiated. Which is nothing new of coure; we both know that very good high feedback amps can and are being made. It's just that I thought it useful to bring it to the attention in a tread extolling the vitues of the Otala amp due to its low feedback making it TIM free. And that's all I claim.
Now what else - oh right. Under the influence of syn08. Apart from the fact that you make it sound like a disease, which I think is slightly overdone 😉 , I hope it is not the case. I really like to think for myself, hell I am even accused of being controverse as a principle. OTOH, we all function in an environment of influences so ultimately you are being influenced by that environment. For better or for worse. But one thing I can tell you: I try very hard not to be under the influence of authority, tradition and religion. So in summary, I think you're barking up the wrong tree here.
Finally, about those quotes. While I am not sure I remember all I have ever said in my admittedly long life, I can't remember that quote. Can you tell me when and where I said something like that?
Jan Didden
dimitri said:
Dimitri, I never said extra 10dB is good. In fact, I didn't say anything about that. I quoted the designer of the Otala-becoming-Electrocompagniet amp.
Jan Didden
Useless posts are deleted. The moderators will discuss what to do to prevent useful threads from being spoiled.
/Hugo
/Hugo
This 10 dB difference is not very important, and only one small group's subjectivity. I actually got them back in 1976 to increase the bias, as it was a little too low for best IM distortion at low levels. Later, they reverted to class B. This often happens when people take a perfectly good general design and start messing it up. Look at what Mark Levinson Audio Systems did to some of my early designs for them. Years later, Mark actually made slower amps, with inferior topologies. Kind of 2 steps back. It happens, when the initial guidance is lost. In this case, Otala. In Levinson's case, me.
The same thing has happened to many audio companies.
The same thing has happened to many audio companies.
john curl said:
John, that may be true.
Yet, both Electrocompagniet and Mark Levinson went on to be very successful and collect accolades about their products on their own. Makes you wonder whether that 'guidance' is really worth anything. Also makes you wonder what it is that sells amps.
Jan Didden