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Old 21st September 2012, 03:09 PM   #1131
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Quote:
Originally Posted by RNMarsh View Post
I would love to be more informed on distortion and masking etal. BUT does that mean we cant do anything except the same single tone or two tone Im test?
I posted a 100 tone 1/10 octave multitone signal (1 minute 24/96), but someone had to host it and I don't know where it is now. I also did an inverse RIAA version. It was setup to repeat at exactly 64K samples so an unwindowed 64k FFT gave exact bins with no leakage. A good sound card gave a very low noise floor in loopback.

Maybe we could revisit this and Jan could host it??
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Old 21st September 2012, 03:13 PM   #1132
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Originally Posted by Joachim Gerhard View Post
Here is an astounding claim from National Semi. I would call that settling time. What happens after an aprupt transient ? How long does the opamp need to pull the output to zero ?

That's pure Bob Pease!
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Old 21st September 2012, 03:13 PM   #1133
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Yes, Pavel, that is one of the TIM tests i do.
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Old 21st September 2012, 04:33 PM   #1134
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
I posted a 100 tone 1/10 octave multitone signal (1 minute 24/96), but someone had to host it and I don't know where it is now. I also did an inverse RIAA version. It was setup to repeat at exactly 64K samples so an unwindowed 64k FFT gave exact bins with no leakage. A good sound card gave a very low noise floor in loopback.

Maybe we could revisit this and Jan could host it??
In order to test an opamp design more thoroughly and more like what we are exposed to when listening, we need to get back to things like this ... because it seems we can hear many tones in listening to music which we cant duplicate in tests thru amps as has been pointed out here... the 'how to' part. But 100 tone would be very helpful as a pointer or marker or dot to connect. I wonder where your good work went. It could then become documented and part of a professional paper/journal. So much to do and so little time.

In the mean time can we also try showing IM data when doing sim's and measurments, please?
Thx - RNM

Last edited by RNMarsh; 21st September 2012 at 04:52 PM.
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Old 21st September 2012, 04:38 PM   #1135
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Here's a link to a typical RF type test that is commonly used.

http://www.ab4oj.com/test/docs/npr_test.pdf

In essence, you would use many tones to create the notch, or a notched white noise source.
Then you measure the noise power only in the notch. With tones, you could likely arrange them so typical IMD products would occur" in the notch"
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Old 21st September 2012, 04:45 PM   #1136
PMA is offline PMA  Europe
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Quote:
Originally Posted by RNMarsh View Post
But 100 tone would be very helpful as a pointer or marker or dot to connect.
No. Try it yourself and you will see. You have to reduce amplitude of individual harmonics to get within Vpp limits and you will approach to noise-like signal. Not enough dynamic measurement range to evaluate the result, it would be hidden in noise.
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Old 21st September 2012, 06:26 PM   #1137
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Originally Posted by PMA View Post
No. Try it yourself and you will see. You have to reduce amplitude of individual harmonics to get within Vpp limits and you will approach to noise-like signal. Not enough dynamic measurement range to evaluate the result, it would be hidden in noise.
There used to be a utility on the AP website, makewave.exe iirc where you could specify the components and also the crestfactor to get around these issues. The output is a table of frequencies with their amplitude and phaseshifts.
You want to specify each component such that the harmonics falls in unique freq bins so you can FFT all individual components and separate harmonics from IM components etc. It's a pretty involved process, and you end up with freqs like 34.774Hz or 12.632kHz, but it is a very powerful music-like test signal allowing extensive analysis of what exactly goes on in your amp under music-like conditions.

Edit: There's also a standardized set of 31 tones according to this protocoll called, not surprisingly, ISO31.

jan
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Old 21st September 2012, 07:24 PM   #1138
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Originally Posted by janneman View Post
There used to be a utility on the AP website, makewave.exe iirc where you could specify the components and also the crestfactor to get around these issues. The output is a table of frequencies with their amplitude and phaseshifts.
jan
You don't get around these issues. There is a minimum crest factor that is possible as you add tones, with lots of tones the signal is noiselike and the expected crest factor approaches 3.1 but you can not make it 1 so the result is to operate almost all the time at -10dB from full scale. Clipping just a single peak crest contaminates the noise floor dramatically.

I wrote a C program to adjust crest factor to a specified peak but usually we wanted high crest factors like 5.3 or 6.1. I never set it up to lower the crest factor to the minimum possible but with lots of tones this is intractable and I would do it iteratively.
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Last edited by scott wurcer; 21st September 2012 at 07:29 PM.
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Old 21st September 2012, 07:37 PM   #1139
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This applies more to loudspeakers but it can be used for electronics too. It would require to measure at many frequencies to be useful. Anyway, usually distortion goes up with frequency and level so i still like the 19kHz-20kHz intermodulation test. "Close-3rd Order" Intermodulation distortion measurement
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Old 21st September 2012, 07:44 PM   #1140
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Seek and ye shall find. Someone has one good solution. Note this is a formula to yield very low crest factor not a solution for the lowest possible. It looks like you can get near to 2 or so at 31.
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