Hi John,
I guess I can try to generate other types of modulation, but here you will see a couple that will be very familiar to anyone working on the IF strip of an FM tuner. These happen to have been taken from a Marantz 2385 I was working on last year.
Because the spectrum analyzer I'm using is a swept type (HP 3585A), it "sees" the results of sweeping the fundamental frequency back and forth at 1 KHz (in this case). The only way you could get something that looks like AM modulation is to capture the fundamental, and the high and low limits only. Otherwise, any sample or sweep will show many of the discrete frequencies as it does here.
I'm not really sure what you did John, can you post what you are seeing?
I downloaded and read the paper on TIM that pooge kindly posted a link to. It explained most of the questions I had with regard to the display under discussion.
One thing I really wonder about in figure 5 where you have compared several op amps looking for dynamic intermodulation distortion. The one part that is missing that would seem to be a poster child for your beliefs. The LM318, speedster of the group. You could have really illustrated your preference for wide band open loop performance by including it in a 20 dB, feed forward configuration. I only ask because it is mentioned just before this comparison was made. Any reason to exclude this part?
-Chris
I guess I can try to generate other types of modulation, but here you will see a couple that will be very familiar to anyone working on the IF strip of an FM tuner. These happen to have been taken from a Marantz 2385 I was working on last year.
Because the spectrum analyzer I'm using is a swept type (HP 3585A), it "sees" the results of sweeping the fundamental frequency back and forth at 1 KHz (in this case). The only way you could get something that looks like AM modulation is to capture the fundamental, and the high and low limits only. Otherwise, any sample or sweep will show many of the discrete frequencies as it does here.
I'm not really sure what you did John, can you post what you are seeing?
I downloaded and read the paper on TIM that pooge kindly posted a link to. It explained most of the questions I had with regard to the display under discussion.
One thing I really wonder about in figure 5 where you have compared several op amps looking for dynamic intermodulation distortion. The one part that is missing that would seem to be a poster child for your beliefs. The LM318, speedster of the group. You could have really illustrated your preference for wide band open loop performance by including it in a 20 dB, feed forward configuration. I only ask because it is mentioned just before this comparison was made. Any reason to exclude this part?
-Chris
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Hi John,
I'm guessing you are responding to my post. I agree, the levels of those blips are way too much to ignore, and should indeed be added into the TIM calculation. I'm just saying that they are not inharmonic and that they are not unexpected when hitting a 741 that hard.
Cheers,
Bob
Actually, Janneman, you DOCTORED with your own (unproven) input. But I won't complain at the moment, unless you are off by a few Hz, and even you are guessing. I have at the moment a FM modulated square wave on my test bench that makes virtually the same levels and frequencies of the glitches that you have named, yourself. I can't tell the difference. So, is it AM or FM that makes up the unmarked frequencies?
Not quite. I didn't measure them, true. But the reference to the 2F2-xF1 is in the paper, and when I calculated those, they fit perfect. It doesn't proof conclusively they actually are that, but it does explain what's on the graph.
But with that stuff you have on your bench you could have a strong argument for the FM case. If only you would get over the point of saying 'I have it!' and actually post some graphs, outline the measurement setup, levels, settings etc! We could talk about contents for a change. You know how that is done, you used to write AES papers, remember?
(BTW If you need some help with the mechanics of posting those graphs or labeling them, just let me know. Only too happy to help out there. Really).
jd
Assumptions? I only took what you guys said in the paper and took it one step further. Are you saying you and Matti and Leinonen were wrong at the time?
Anyway, does that mean you have no intention to provide anything tangible on this? Too bad.
jd
Another question to ask is where are all the missing intermods if these are at different frequencies? Suddenly numerous expected tones are absent with others at "almost" all the same frequencies. Pretty far fetched. BTW it is clear from your graph that evens are present so all those even order intermods are expected.
As an asside I would experiment with a low frequency tri-wave of different slopes and high frequency tone. Since the tri-wave is constant slope it's "quadrature" is a DC level. This would allow a better exploration of the shape of the input non-linearity. Also the error signal in the presence of feedback is more seperable in the low vs high OLBW cases.
Let me help you once more John, because clearly you still haven't re-read your own paper. This is what YOU said in YOUR and Matti's and Eero's paper. Do you now say this was BS? Are you now saying that it was wrong, that since then you have found The Truth (tm), which however you seem unable or unwilling to back up in any way? Did you tell Matti and Eero that they too, had it all wrong in '76?
jd
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It is not BS, it is an error. Whether Matti made an error in presuming that a certain group of pips were caused by 2F-N IM, or Mitch Cotter allegedly made an error by seeing the same pips as FM, both were trying to find the 'truth' in the matter.
One thing that 'irks' me, and has for years, is that nay sayers can say NO to just about anything, and IF they are wrong, we are all supposed to shrug our shoulders and go on.
However, if I, or one of my colleagues, in pursuit of new knowledge, goes down the wrong path, or our 'hypothesis' doesn't pan out, we are vilified as BS'ers, troublemakers, and time wasters by the mob. Give it a break, will you? I can't personally PROVE everything, and I don't have the strength or interest to teach the basic stuff that has already been researched.
I can only offer 'audio wisdom' or whatever it is, at this point in my life. If that is not enough, or no one wants to take me seriously, then my time to contribute here is done.
I, too, have better things to do, at least that is what my associates tell me.
By the way, Jan, interesting amp you are making. We are not taking the same approach in our new amp, so we have no conflict, but now I understand your further interest in my new amp. Sorry, our schematics are still secret and patent protected. Take it, or leave it. Most likely, I will be doing a 'dog and pony' show with the amp at Denver Rocky Mountain, in Oct. Depends on the doctors clearing me to travel, by then.
One thing that 'irks' me, and has for years, is that nay sayers can say NO to just about anything, and IF they are wrong, we are all supposed to shrug our shoulders and go on.
However, if I, or one of my colleagues, in pursuit of new knowledge, goes down the wrong path, or our 'hypothesis' doesn't pan out, we are vilified as BS'ers, troublemakers, and time wasters by the mob. Give it a break, will you? I can't personally PROVE everything, and I don't have the strength or interest to teach the basic stuff that has already been researched.
I can only offer 'audio wisdom' or whatever it is, at this point in my life. If that is not enough, or no one wants to take me seriously, then my time to contribute here is done.
I, too, have better things to do, at least that is what my associates tell me.
By the way, Jan, interesting amp you are making. We are not taking the same approach in our new amp, so we have no conflict, but now I understand your further interest in my new amp. Sorry, our schematics are still secret and patent protected. Take it, or leave it. Most likely, I will be doing a 'dog and pony' show with the amp at Denver Rocky Mountain, in Oct. Depends on the doctors clearing me to travel, by then.
OK, understood.
John, you are calling this off on yourself. Nobody is singling out you or your associates. But can't you get it through your scull that people WILL NOT accept an offhand remark like 'it's FM', and then when asked why, get some tapdancing like 'because Mitch told me and he worked for Marantz' or 'because Jack Bybee took me to lunch and he has a Bentley'. All totally irrelevant stuff, and only reinforcing the impression that you just blabber out something. I'm not saying you do, I'm saying you project that impression.
Edit: I'll get out of here. There's no point, and I don't want to project the impression I'm hunting JC. I'm not.
jd
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Before you go, Jan, PLEASE note the SYMMETRY or lack of it, of the pips that you labeled, and then recheck your math and the predicted frequencies of the 2F-N products that YOU put into the graph, and see if they ARE symmetrical as well. They aren't, by my calculations, how about yours? Did I overlook something?
John, they all line up. That's just the way it is. Let go of it and move on. I will also move on, the peanut gallery is agitated again and they should find peace.
I don't think so, check again. Please look carefully, this time at 2f2-8f1, and 2f2-6f1. Symmetrical to 2f2-9f1, and 2f2-7f1, respectively? I think not. Yet, the frequencies on the graph are symmetrical. Look, I don't mind being proven wrong, just do it properly. This is now between Mitch and Matti, I am only the messenger.
PS. Jack Bybee says hi!
PS. Jack Bybee says hi!
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Hi John,
Sooo, you're telling us that no one inspected the signal fed to the spectrum analyzer with an oscilloscope at the time? Good lord man! I'd think the very most important thing any researcher (especially one at the engineer level such as yourself) would do is to verify what it is that they are measuring. An oscilloscope would have clearly showed the presence of AM modulation, as I'm sure you are well aware.
Given the fact that you are somewhat unsure of what the graph is indicating, you would want to run that test again. Just so you could appear to know what you are pointing out to us. Maybe some time I will do this. I'll have to set up another signal generator so I can exactly duplicate what you fellas did way back when. I even have some 741s hiding out somewhere here. If you could, can you sketch out your test setup? I'm not exactly sure how you guys mixed the two signals at the time and I would like to exactly recreate your setup. Did you use a selective voltmeter, or a spectrum analyzer? My bet is on the selective voltmeter, but I'd like to be sure.
Again John, why wasn't the LM318 tested? It's absence is a glaring one.
If you'd rather, you can email me a sketch of the test setup. I will then send you a sketch of the test setup as I have constructed it for your inspection. I can even take a picture if you'd rather. Then I'll run the experiment and we can talk back and forth in order to confirm it's done right. I am happy to report the actual results without drawing any conclusions at all. I'll be more than happy to allow those with a professional background to assess what is going on. It may take me some time, but we can get through this. John, I am absolutely sincere about my offer.
If you have a problem with me doing this, pick someone else. Either way, let's get some results you can be sure of. No one has to be embarrassed by returning to some earlier work to verify everything. Sound good to you John?
Anyone else interested in re-examining this critical work? I'm sure we'll come out with the same findings as the original tests, they were conducted carefully so as to withstand peer review.
-Chris
Sooo, you're telling us that no one inspected the signal fed to the spectrum analyzer with an oscilloscope at the time?
Good lord man! I'd think the very most important thing any researcher (especially one at the engineer level such as yourself) would do is to verify what it is that they are measuring. An oscilloscope would have clearly showed the presence of AM modulation, as I'm sure you are well aware.Given the fact that you are somewhat unsure of what the graph is indicating, you would want to run that test again. Just so you could appear to know what you are pointing out to us. Maybe some time I will do this. I'll have to set up another signal generator so I can exactly duplicate what you fellas did way back when. I even have some 741s hiding out somewhere here. If you could, can you sketch out your test setup? I'm not exactly sure how you guys mixed the two signals at the time and I would like to exactly recreate your setup. Did you use a selective voltmeter, or a spectrum analyzer? My bet is on the selective voltmeter, but I'd like to be sure.
Again John, why wasn't the LM318 tested? It's absence is a glaring one.
Then you should be able to understand why others are irked when you come out with a statement and use every trick in the book to avoid providing any proof. No one is chasing you John, you are merely being asked to back up your statements. In fact, we are even being polite about it.
Actually, that is patently untrue. Your statement reflects exactly what you do if someone else makes a statement in your presence that you want to pick apart. Stop throwing bricks my friend, you do live in a glass house as it were. If you'd like to have an error slide, try admitting to it and allowing others to err as well. Otherwise you, will tend to receive the treatment you give others.
If you'd rather, you can email me a sketch of the test setup. I will then send you a sketch of the test setup as I have constructed it for your inspection. I can even take a picture if you'd rather. Then I'll run the experiment and we can talk back and forth in order to confirm it's done right. I am happy to report the actual results without drawing any conclusions at all. I'll be more than happy to allow those with a professional background to assess what is going on. It may take me some time, but we can get through this. John, I am absolutely sincere about my offer.
If you have a problem with me doing this, pick someone else. Either way, let's get some results you can be sure of. No one has to be embarrassed by returning to some earlier work to verify everything. Sound good to you John?
Anyone else interested in re-examining this critical work? I'm sure we'll come out with the same findings as the original tests, they were conducted carefully so as to withstand peer review.
-Chris
For everyone else, it is important to do the math and calculate what Jan (and even Matti) thought these pips to be, and then compare them to the real measurements on the graph, and check through interpolation between the measured points if the measurements exactly match the calculations. It's high school math!
We tested just about everything, Anatech. We published maybe 1000th of the actual measurements done at the time. I personally took home a stack of several inches thick of measurements, done by myself.
The 318 is fast, so it doesn't show TIM effectively. It appears to have other problems. We later proved, in fact, that any slew rate of 5V/us or more for a preamp, was probably good enough, but that was a few years later. THIS paper was to show a TEST PROCEDURE to measure TIM. We used our most obvious examples to prove it to measure what it is supposed to measure.
The 318 is fast, so it doesn't show TIM effectively. It appears to have other problems. We later proved, in fact, that any slew rate of 5V/us or more for a preamp, was probably good enough, but that was a few years later. THIS paper was to show a TEST PROCEDURE to measure TIM. We used our most obvious examples to prove it to measure what it is supposed to measure.
Hi John,
Thank you for the explanation. That's all I really asked for. You have to admit, mentioning this device in the text, then excluding it does make people wonder. It appeared as a device that would support the statements made in that paper, to have it missing raised questions. I would have thought that including it would show the test itself wasn't creating some of what you were seeing as TIM. A control if you will.
If you don't mind me asking, any idea of the other issues the LM318 had?
I'll assume that stack of data you took home was lost in your fire. Too bad really. I'm sure there must have been a wealth of information in there.
As for high school math, I have no wish to revisit that experience. Math was not my strong suit and I avoid it if possible. I also see working things like that out as a waste of time. If you're wondering, I really hate fishing!
-Chris
Thank you for the explanation. That's all I really asked for. You have to admit, mentioning this device in the text, then excluding it does make people wonder. It appeared as a device that would support the statements made in that paper, to have it missing raised questions. I would have thought that including it would show the test itself wasn't creating some of what you were seeing as TIM. A control if you will.
If you don't mind me asking, any idea of the other issues the LM318 had?
I'll assume that stack of data you took home was lost in your fire. Too bad really. I'm sure there must have been a wealth of information in there.
Walt Jung actually stated that the needs were more modest than that even. That was in his earlier book around that time. I would agree with that depending on how high you wanted your frequency response to go.
As for high school math, I have no wish to revisit that experience. Math was not my strong suit and I avoid it if possible. I also see working things like that out as a waste of time. If you're wondering, I really hate fishing!
-Chris
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