John Curl's Blowtorch preamplifier part II

[Wavebourn]

Originally Posted by Edmond Stuart

Limiting the OL gain at LF is plain B******T.

Sure, it is not the same as linearizing stages, despite results seems to look similar.

Excess gain of each and every stage may be turned into their better linearity, lower output impedances, higher input impedances, over the wider frequency band, that means less of OL distortions generated by their own non-linearity and non-linear coupling between them.

[scott wurcer]

I leave it to you guys, I'll be traveling in Asia off and on till the end of November. Have to miss BA, unfortunately. I still would like to see the theoretical underpinings of the inharmonic frequencies, not holding my (political) breath.

[Wavebourn]

Originally Posted by scott wurcer

I leave it to you guys, I'll be traveling in Asia off and on till the end of November. Have to miss BA, unfortunately. I still would like to see the theoretical underpinings of the inharmonic frequencies, not holding my (political) breath.

Are intermodulations harmonic?

Good luck with your trip!

[janneman]

Originally Posted by Bob Cordell

Hi John,

I'll look forward to seeing you at the show.

This is fine to not dwell on TIM and PIM.

I also agree with you on the healthcare debate, which is depressing and dismal. We may disagree on the details, but we probably agree that some kind of change is needed and that the current process for that change is frustrating.

One thing I'll throw in on the open loop bandwidth issue: I believe that those who design for wide open loop bandwidth often by necessity and nature pay more attention to open loop linearity than many do who use a lot of NFB. Of course, there are MANY exceptions to this, including myself and many others here who take open loop linearity very seriously.

To me, one of the core questions is the following: construct two amplifiers identically, with the same NFB gain crossover. Let them both have 30 dB NFB at 20 kHz. Let them both have very good open loop linearity. Let them both be highly stable with good gain and phase margin. By some quality means, limit the low-frequency gain of the second one so that the open loop bandwidth is 20 kHz in the second amplifier.

Do they sound different?

Which one sounds better?

Speculation on why they sound different if they do.

Cheers,
Bob

Bob,

I understand what you are saying, and at first glance it seems very unlikely (to phrase it somewhat more subtle than Edmond ) that an amp starts to sounds better by decreasing the lf open loop gain, all else being equal. But is that a realistic comparison? If a designer who subscribes to the notion that high open loop bw is important designs the same amp wrt spec sheet, as a designer who believes in high fb factor, all else will not be the same. So there may well be an audible difference between those amps that perhaps is ascribed to the different OL bw but may be caused by other differences between the designs.

jd

PS Just when I have decided to skip RMAF this year, two of my heros decide to go there. Bummer.

[john curl]

And you will never learn anything new, Scott, if you don't ask your colleague, Dick Sequerra. He is the one who first showed me, along with Mitch Cotter. You have to ask, and be willing to listen. We sit back, amazed that you won't.

[janneman]

Originally Posted by john curl

And you will never learn anything new, Scott, if you don't ask your colleague, Dick Sequerra. He is the one who first showed me, along with Mitch Cotter. You have to ask, and be willing to listen. We sit back, amazed that you won't.

Wow! Are you suggesting that ALL of us who want to know, all of us start calling Dick? What a concept!

jd

[john curl]

Wavebourn, IM byproducts are also related to the music played. This can be proven. There is an Ampex paper written in the early '60's that proves this. However, extra distortion byproducts that are NOT IM or harmonic related, are NOT related to the music and are more easily heard by the individual as 'out of place' so to speak. This, we think, is an important key to quality listening.

[janneman]

Originally Posted by john curl

Wavebourn, IM byproducts are also related to the music played. This can be proven. There is an Ampex paper written in the early '60's that proves this. However, extra distortion byproducts that are NOT IM or harmonic related, are NOT related to the music and are more easily heard by the individual as 'out of place' so to speak. This, we think, is an important key to quality listening.

I can understand that, they are completely dissonant and will be very objectionable. The question is: are they there, and if so, where do they come from?

jd

[scott wurcer]

John, I'll give $10,000 to research toward macular degeneration if you can produce one reference for the production of totally inharmonicaly related frequencies from a simple op-amp circuit.

[john curl]

No, Jan, this does not concern you. Scott is personal friends with Dick Sequerra, but he never asks the important questions, and Dick lets him stay in the dark. You should hear my discussions with Dick Sequerra, they would be completely alien to Scott, at this juncture. However, I am on the path of enlightenment, so my questions are answered by people with more experience than me in specific areas.
The hear no difference, measure no difference crowd are going to have a different dialogue with someone like Dick Sequerra. It just isn't worth it to him to bang his head against the crowd, and he chides me about wasting my time with dialogue on line, when I could be doing something more useful.