Because I am trying to move a stale conversation out of the 1980s and into the 21st century.
@ScottJoplin. Why does a little more IMD matter. If 19+20k produces a 1kHz spur then it hits where there is 60-100dB of feedback to supress it. So I don't see the issue, esp when a GBFB amp still has less distortion that the expensive no feedback audio jewellery at those frequencies.
@ScottJoplin. Why does a little more IMD matter. If 19+20k produces a 1kHz spur then it hits where there is 60-100dB of feedback to supress it. So I don't see the issue, esp when a GBFB amp still has less distortion that the expensive no feedback audio jewellery at those frequencies.
So one would think. It's an argument I've seen used. Why do people say HD measurement has less value than IMD when the mechanisms that cause them are the same? Does IMD directly correlate to HD?
You know me, I think 32 tone tests are the way forwards as they give a better picture on what happens with a music-like harmonic structure. Actually it's way more testing that real music.
I agree, but not everyone knows how to do multi-tones or, to interpret the results!
So when your only tool is a hammer, all your problems start to look like nails. ;-)
Jan
So when your only tool is a hammer, all your problems start to look like nails. ;-)
Jan
Whereas I have a set of hammers from toffee hammer, through pin hammer all the way to sledge hammer 😀.
It was an English thing. You used to get bars of Toffee under the bluebird brand that were impossible to eat without breaking them up. The xmas presentation packs that Grannies always bought to rot their grandchildrens teeth came with a special hammer for the job.
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In itself that doesn't mean a lot. If you start higher and roll off earlier, you might still have the same open loop gain at, say, 20kHz. And that is what counts for distortion reduction.
If two opamps have the same open loop gain at 20kHz, the one that has more at say 20Hz has a lower distortion in the audio band, for the same closed loop gain.
Jan
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I get it Jan.
And I'm grateful for this thread. I've seen the light. I've been freed from the tyranny of numbers! I now see that all those years in engineering school were wasted.They teach you all that math and now I see that numbers are arbitrary and nothing but a Masonic conspiracy. I already threw my engineering calculator in the recycling bin. Logarithms - bah! Who needs them? Trigonometry? Obviously fake. How could I have ever believed that stuff? It's just meaningless group think. I can now dispense with numbers and move forward in Reality. How liberating!
And I'm grateful for this thread. I've seen the light. I've been freed from the tyranny of numbers! I now see that all those years in engineering school were wasted.They teach you all that math and now I see that numbers are arbitrary and nothing but a Masonic conspiracy. I already threw my engineering calculator in the recycling bin. Logarithms - bah! Who needs them? Trigonometry? Obviously fake. How could I have ever believed that stuff? It's just meaningless group think. I can now dispense with numbers and move forward in Reality. How liberating!
Uhhh ... I don't think you quite got it yet 😕
Unless there's a huge tongue in your cheek?
But, just in case: the attached illustrates the situation. Just disregard the frequency and magnitude scale numbers, I couldn't find a better one, but it is about the shapes.
These are the open loop gains of two amplifiers, that are used to get a certain closed loop by wrapping a feedback loop around them.
The top one (thin line) clearly has the smallest OL bandwidth.
Yet, for all frequencies below the turnover frequency of the (lower) wide-band amp, it clearly has more distortion reduction that the bottom (thick line) one with the wider bandwidth.
In fact, in this example, the top one, smaller OL bandwidth amp, has either more or the same distortion reduction than the lower, wide bandwidth one.
Jan
Unless there's a huge tongue in your cheek?
But, just in case: the attached illustrates the situation. Just disregard the frequency and magnitude scale numbers, I couldn't find a better one, but it is about the shapes.
These are the open loop gains of two amplifiers, that are used to get a certain closed loop by wrapping a feedback loop around them.
The top one (thin line) clearly has the smallest OL bandwidth.
Yet, for all frequencies below the turnover frequency of the (lower) wide-band amp, it clearly has more distortion reduction that the bottom (thick line) one with the wider bandwidth.
In fact, in this example, the top one, smaller OL bandwidth amp, has either more or the same distortion reduction than the lower, wide bandwidth one.
Jan
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Gotta agree there. What gets forgotten in all these conversation is that HD and IMD are the names of tests, not program material playback errors. They're ways to measure nonlinearity. They aren't directly the things we might hear with music. Might hear effects of the nonlinearity, but not simple harmonic distortion or two-tone IMDs or even equal-level multitone distortion. There's not 0.1% distortion when you listen to an amp that measures 0.1% at its rated power or even at other powers. Just like when you have a speaker that measures -3dB down at 20kHz, it doesn't mean that the energy at 20kHz is just half of what is playing at 1kHz when you're playing Bach!
edit: though, there is a point about the relative limitations of such tests. For instance, if there were a brick wall lowpass filter on a power amplifier at 21kHz, then even a horribly distorting amplifier when fed 12kHz would measure zero THD, while a two-tone third order IM test at 12kHz + 12.1kHz would reveal some ugliness. But theyre still just names of tests, not of garbage generation in all conditions.
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I thought my sarcasm was obvious. Just to clear up any misunderstanding, I didn't really throw out my engineering calculator, and I still use logarithms and trigonometry. 😉 I'm still a slave to Masonic dogma. 😛
What you explain is right out of Walt Jung's IC Op Amp Cookbook. It's basic stuff to me. That's what I mean when I say I get it.
Thanks, that's a big relief. We need all the brains here we can get ;-)
And I am sure Walt got it from much earlier times. I have a 1954 book that explains it.
This whole knowledge bloomed during and after WWII - nothing so advantageous to technical knowledge and progress as a good war!
Jan
And I am sure Walt got it from much earlier times. I have a 1954 book that explains it.
This whole knowledge bloomed during and after WWII - nothing so advantageous to technical knowledge and progress as a good war!
Jan
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Yes, the knowledge is generally applicable. It goes back further than 1954 too. Nyquist stability criteria and Bode plots were first described in the 1930s Nyquist stability criterion - Wikipedia Bode plot - Wikipedia . It was at least 20 years before this was widely applied. Today they're indispensable for design of modern feedback amplifiers.