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Old 20th September 2012, 06:57 AM   #1061
fas42 is offline fas42  Australia
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Quote:
Originally Posted by RNMarsh View Post
Its as valid as a single tone or two tones or three tones or multiple tones (AP) we use now... just more tones. Its a way to gauge the total level of all the harmonics generated... similar to when music frequencies are the input being worked upon.
OK, mental exercise: have 20,000 amplifiers with those distortion characteristics, each one is fed a separate pure sine wave of the group that makes that complex waveform, and then combine their outputs, appropriately attenuated, in a "perfect" summing device. And alternatively, have a single such amp fed with the complex waveform made up of 20,000 sine waves; compare the output of that with the summing device. Will they match?

Frank
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Old 20th September 2012, 08:07 AM   #1062
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You will have to lower significantly the levels of 20,000 harmonics in a single amplifier example to prevent overload/clipping, so they can never match
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Old 20th September 2012, 08:11 AM   #1063
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Quote:
Originally Posted by fas42 View Post
OK, mental exercise: have 20,000 amplifiers
Will they match?

Frank


Before jumping to the 20000 number, why don’t you start this mental exercise with a two tone signal, two amplifiers and a two input perfect summer, then may be go to a three tone signal, three amplifiers…
By progressing this way, one at least has the chance to figure a pattern emerging

George
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Last edited by gpapag; 20th September 2012 at 08:25 AM.
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Old 20th September 2012, 08:15 AM   #1064
PMA is offline PMA  Europe
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In a real world, these 2 examples will never match (noise level etc.). In a purely theoretical example when omitting some real parameters they may match.
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Old 20th September 2012, 09:16 AM   #1065
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Originally Posted by abraxalito View Post
How did that allow you to create your own multitone test waveforms?
Moved the goalposts, I saw what you did there. It had two tone capability as was the norm for IM testers. Like I said, not as flexible or versatile as modern instruments, but certainly multitone.
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Old 20th September 2012, 09:20 AM   #1066
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Originally Posted by RNMarsh View Post
Would it be audible if the detection threshold is .05% or less? Should be. -RNM
Big "if" in the presence of 19,999 other full scale tones. Strikes me that using a musical signal where you feel there's a difference (or mirable dictu, actually demonstrated audibility of a difference) and nulling it against the input might give a clue?

If you want to get a frequency resolution narrow enough to let you look at all of the space between the 20,000 tones, the measurement time would be rather long.
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Old 20th September 2012, 09:21 AM   #1067
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Ah but in my idiolect 'multitone IMD' is distinct from IM - meaning more than two-tone intermod. So the goalpost moving was your own
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Old 20th September 2012, 09:30 AM   #1068
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I can't be responsible for you wishing to define words in the manner of Humpty Dumpty.

Back to discrete opamps (I think y'all ought to use tubes).
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Old 20th September 2012, 09:31 AM   #1069
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Quote:
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I can't be responsible for you wishing to define words in the manner of Humpty Dumpty.
False premise.
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Old 20th September 2012, 10:29 AM   #1070
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Originally Posted by fas42 View Post
OK, mental exercise: have 20,000 amplifiers with those distortion characteristics, each one is fed a separate pure sine wave of the group that makes that complex waveform, and then combine their outputs, appropriately attenuated, in a "perfect" summing device. And alternatively, have a single such amp fed with the complex waveform made up of 20,000 sine waves; compare the output of that with the summing device. Will they match?

Frank
Let me try:

You have 20k amplifiers each having a transfer characteristic 'A', each being fed a signal S1....S20k. Each amp output is thus A*S1....A*S20k. After the perfect summer you have A*(S1+S2+...S20k).

Now take a single 'A' amp and feed it (S1+S2...S20k). Output will be A*(S1+S2...S20k).

Looks like a match to me. Of course, we could have skipped all of this by just invoking the superposition principle

jan
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