Bob Cordell Interview: BJT vs. MOSFET

[john curl]

Otala was being stubborn.

 

[ingrast]

.......
I do like to pursue low distortion measurements because when an amplifier has very low THD or twin tone, there is a lot less wiggle room for crossover distortion and other more unexpected nonlinearities to be there. ....
Bob

Rodolfo

 

[ingrast]

What's in a word

Mr. Curl

I am confident most of us are more interested in improving our designs than in a stubborn defence of pet conceptions.

It should greately help to elaborate further on what is meant by listening test. I am certain you have gathered during a long career dedicated to audio, evaluation criteria you could share with us.

I am not asking for objective data since this is precisely what you do no rely upon as definitive criteria. I am rather asking you to share the type of audible qualities you pay attention when evaluating an amplifier. The kind of details you focus on, which to an unwary ear may go unnoticed.

Rodolfo

 

[mikeks]

Hi John,

I think your remark is a bit condescending and presumptuous, and unfair to the people on this forum. I believe that most of the people here listen very carefully to what "professionals" like yourself say, but that does not mean that they will accept it at face value and never challenge it. You just don't like to be challenged.

I would very much love to have Chas participate here and share his experiences with EC himself. That way we can have some back-and-forth dialog. What you shared was hearsay and it had very little value because we have no way of finding out the details. Chas, if you are listening, please join in!

Implying that those who are not "professionals" (i.e., make a business out of audio) are not as good at making high-end amplifiers is just as bad as one saying that one cannot make a good amplifier without having an EE degree. Similarly, implying that those on this forum don't listen to their gear as ardently as you is also wrong. How is it that only "audio professionals" and audio reviewers are the only ones blessed with good hearing and knowledge of how to listen? Quite a coincidence, isn't it?

Finally, you do not have a monopoly on linearity in the open loop design of power amplifiers. To imply that those on this forum design less linear amplifiers and then fix up the problem by applying a lot of NFB is also wrong.

I always enjoy your participation on the forum and hope you will continue. Just keep in mind that you will get pummeled with tomatoes just as much as anyone else here if you say something that some don't understand or agree with. No free passes for "professionals".

Cheers,
Bob

Amen!

 

[mikeks]

JC, you have NEVER shown how some form of non-linearity (including SID) may not be also expressed in the THD+N measurement.

All you do is frantically wave your hands about this bit of 1960s or that bit of 1970s gossip. Not helpful at all, I am afraid.

 

[john curl]

How about Hirata distortion? Do you even know what I am talking about?

 

[john curl]

Also, PIM distortion or FIM distortion which is the same thing. You know , FM modulation. Can you measure that with harmonic distortion analysis? You people are like children, which just shows how old and experienced I am. ;-)

 

[Bob Cordell]

Also, PIM distortion or FIM distortion which is the same thing. You know , FM modulation. Can you measure that with harmonic distortion analysis? You people are like children, which just shows how old and experienced I am. ;-)

Hi John,

First and foremost, I must say that I do love your wry sense of humor, and will always enjoy sharing a drink with you. I do miss the old days at the AES.

PIM cannot be measured with THD, but it has been my experience that it is almost impossible for an amplifier with very low THD to generate any PIM, since the same nonlinearities that cause PIM will almost inevitably cause other distortions. But one does have to be careful about using the word NEVER. That's one of the reasons that I like THD and twin-tone IM to be low - that leaves almost no wiggle room for something like PIM to sneak in. Nevertheless, I do measure PIM; but the equipment to do so is so specialized that most people cannot be expected to be able to measure it.

There is an important caveat: I am pretty sure that it can be shown theoretically that PIM will generate sidebands in a spectral analysis, just like FM or phase modulation. In fact, I think that the only difference between AM IM and PIM is the relative phase of the sidebands on either side. So a sensitive, narrow-band spectral analysis may indeed not let PIM escape.

How's the traffic out there after that idiot in the tanker truck destroyed that on-ramp? The pictures were incredible, and brought back memories of the earthquake damage.

Cheers,
Bob

 

[john curl]

Keep your sense of humor, Bob. I will try as well.

 

[john curl]

delete

 

[mikeks]

How about Hirata distortion? Do you even know what I am talking about?

Red herring.

 

[john curl]

To you, perhaps. Not to me.

 

[Christer]

Interesting, google came up with at least three different Hiratas, who all published papers on distorsion, although in such diverse areas as liquids, gravitation and audio.

 

[john curl]

Which one do you think I was referring to?

 

[ingrast]

Mr. Curl:

Did you notice this post ?

Rodolfo

 

[Bob Cordell]

Which one do you think I was referring to?

Like I said, I love your sense of humor!

Bob

 

[Christer]

Which one do you think I was referring to?

Living in California, you are probably most worried about gravitational distorsion.


I just found it amusing there were so many guys with the same name publishing scintific papers on various types of distorsion, but maybe Hirata is as common in Japan as Jones is in England?

 

[Cal Weldon]

Red herring.

Please tell us why you posted this without explanation.

 

[Christer]

Will you folks ever progress if you doubt what other professionals say?

This is the same old discussion that has taken place many times before. I don't think the problem is that people ignore or doubt the professionals. The problem is your opinions are so different you cannot all be right. It is a bit like different religions. Both you and Bob say we should use feedback, but Charles disagrees. You say the OP should use BJTs, Bob says it should use VMOS and Charles says it should use laterl MOS. Etc, etc... There is no concencus, just different opinions and experiences. I do listen to what you say with great interest. I do listen to what Charles say, also with great interest. I do listen to what Bob says, still with great interest. However, at the end of the day, I have to weigh all these opinions, claims and experiences against each other and melt them down together with all the others say. So I am sure many of us do pay attention and appreciate what you guys tell us, but none of you can be expected to be the only god. Besides, it is often the discussions, like this thread, where you argue with each others that are the most rewarding ones for learning. How boring wouldn't it be if you all agreed.

 

[jacco vermeulen]

maybe Hirata is as common in Japan as Jones is in England?

Sidenote: it is, Hira is a mountain in Japan. Probably all Japanese names have their roots in shinto.

Maybe because all are part right, but none have all the answers.
Considering that Mr Curl posted himself that he is old, i too am interested in the answer to Rodolfo's question.