HI Stuart
Go to page 1 in this thread
http://www.diyaudio.com/forums/analog-line-level/146693-john-curls-blowtorch-preamplifier-part-ii.html
You will also find it at the end of BT thread 1
http://www.diyaudio.com/forums/solid-state/71189-john-curls-blowtorch-preamplifier-2002.html
It’s a never ending story.
Cheers
Free software can handle complex fft, as well as MathCad which I'm familiar with so a software implementation of Bob's PIM measurement should be possible
but as you say a precondition for making the effort would be whether anyone would be swayed by the results or if ossification of their position is complete
You mean this one and following??
http://www.diyaudio.com/forums/anal...owtorch-preamplifier-part-ii.html#post1867760
http://www.diyaudio.com/forums/anal...owtorch-preamplifier-part-ii.html#post1867760
you mean where Walt points out that "low open loop bandwidth" and "high negative feedback" are NOT the responsible factors in TIM?
I do not know, i thought they were asking for image location of assumed 'non-harmonic' components in a FFT record.
To me, it makes absolutely no sense to examine FFT of dynamically clipping circuit. And it is the case here, the measured uA741 operated in a slew rate limitation mode, SR clipping mode. Then there is no feedback and just slow charging of internal capacitances by a current limited to some value.
Everyone knows that Vc = 1/C * integral of (Ic.dt) + Vo
When the capacitances are charged and output dV/dt is slew rate limited, it makes no sense to analyze output spectrum under such conditions.
Everyone knows that Vc = 1/C * integral of (Ic.dt) + Vo
When the capacitances are charged and output dV/dt is slew rate limited, it makes no sense to analyze output spectrum under such conditions.
Here's one of the pics from back there, with values filled in for the red-circled frequencies you were asking about. They look like IM products to me.
I remember reading through that part of the thread awhile ago and not understanding what the fuss was about. Still don't. 😕
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We have a library built-in. I would try something like a 4M point FFT and make the frequencies exact bins so there would be no question. If you use a small angle approximation simple trig identities will yield the phase modulation. Sin(wt+phi)*Cos(wt), if the phase modulation is small phi drops out. I tried this with FFTs and a synthesized waveform and it seemed to work.
Godfrey, John claims some tones are 50Hz off, I don't see it. Claiming to read within 1% on that plot is rather optimistic. This plot has become like the Zapruder film or that photo of Sasquatch. I think at times folks use the uncertainty to promote an agenda.
What this is called, in my opinion, is finding enough IM products to FINALLY complete the series, at least in theory. This bypasses the existence of FM distortion.
To ME, it is a bit like the alternative explanation of the orbit of Mercury, by putting a planet on the other side of the Sun from the Earth, in the same orbit. It can be made to fit, within practical measurement.
Scott's and many others assertion COULD be correct. However, it doesn't look consistent with the other MISSING IM products or in the relative magnitude of the questionable IM byproducts, compared to lower order IM byproducts. I tentatively stand by my position, that we are seeing a superposition of IM and FM byproducts, but I too would have to repeat the test to PROVE it.
To ME, it is a bit like the alternative explanation of the orbit of Mercury, by putting a planet on the other side of the Sun from the Earth, in the same orbit. It can be made to fit, within practical measurement.
Scott's and many others assertion COULD be correct. However, it doesn't look consistent with the other MISSING IM products or in the relative magnitude of the questionable IM byproducts, compared to lower order IM byproducts. I tentatively stand by my position, that we are seeing a superposition of IM and FM byproducts, but I too would have to repeat the test to PROVE it.
Okay. But we are not able to measure anything like shown, for the up-to-date fast enough part/circuit (and we have 40-60dB more sensistive methods). Thus, I do not see any explanation provided in this obsolete 741 measurement.
This is the strangest arguement, a magnitude only plot can not separate the two and ALL tones are at the sum and difference frequencies. I saw Ron's paper, an LM358, LM1458, and a 1969 Harmon Kardon receiver. I don't get it, not a single modern device of any kind, it's not as if he doesn't have access to them.
EDIT OK John I just entered the graph into a tool we use when we only have a scan and no data for a graph. 2F2-11F1 is 4.998 vs 4.98 and the 2F2-7F1 is 7.738 vs 7.74. Next....
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Apparently Scott, you forgot that on post #6550 that you asserted that it had to be: 2f2-8f1, which is 4.56 KHz by my calculations. Yet it might just be 2f2-11f1 instead, I agree that it COULD be: 2f1-11f1, and it could be that the planet Vulcan is behind the Sun right now. How can I know for sure? Can you? 4.56 KHz would be off by 40 Hz or so, would it not?
John your twisting my words, I assumed that was what we had agreed upon last year. Godfrey's plot clarifies that. I simply meant is has to be AF1+-BF2 and without the phase this test cannot tell PIM from TIM.
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please get rid of those obsolete, historical and unreliable measurements and switch to something contemporary and more useful. I am old enough to dare to say that 🙂
My feeling is that we are reviving old ghosts and old quarrels, rather than finding real answers.
My feeling is that we are reviving old ghosts and old quarrels, rather than finding real answers.
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