John Curl's Blowtorch preamplifier part II
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 7th September 2009, 12:50 PM #1041 diyAudio Member   Join Date: Sep 2005 Location: Trnava, Slovakia
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Join Date: Aug 2005
Location: Toronto
Quote:
 Originally Posted by gerhard The test board ... and now back to paid development work
Off topic, I'm really surprised, since when is Maxim doing LT1028? There's no trace of that in their catalogue, though your picture seems to show a genuine Maxim part...

 7th September 2009, 02:24 PM #1043 diyAudio Member   Join Date: Jul 2003 Location: berkeley ca Gerard, I don't know how you did it, but you completely missed what we were arguing about. At first I thought you were clarifying the situation, but you didn't put in the IM byproducts in actual contention. You appear to have ignored them. Please everyone, the two most obvious 'pips' on the graph that really depart from being an IM byproduct are alleged to be: 2F2-8F1, and 2F2-6F1. They compute to be: 4.56 KHz for 2F2-8F1, and 10.92 KHz for 2F2-6F1. Do they appear on the actual test (fig 3) to be these frequencies? Did I do my math wrong? This is the actual problem.
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Join Date: May 2008
Location: Toronto
Quote:
 Originally Posted by gerhard The questionable frequency pair in high resolution: Squarewave = 3180 Hz ==> 1380 Hz Squarewave = 3210 Hz ==> 1110 Hz IMD product wanders 270 Hz down for input step of 30 Hz =====> This is IMD with 9 * square wave frequency. Methinks this argument is settled. The not so funny thing is that everybody with a tone generator and a soundcard could have done this in one evening, but nobody did it.
What a breath of fresh air! Nicely done!

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Join Date: Sep 2002
Location: Sacramento, CA
Quote:
 Originally Posted by john curl Please everyone, the two most obvious 'pips' on the graph that really depart from being an IM byproduct are alleged to be: 2F2-8F1, and 2F2-6F1. They compute to be: 4.56 KHz for 2F2-8F1, and 10.92 KHz for 2F2-6F1. Do they appear on the actual test (fig 3) to be these frequencies?
They don't appear to, no.

Even though the peaks in fig. 3 are skewed such that they don't match up with the actual numbers, when 2F2-8F1 and 2F2-6F1 are added to the graph I made previously, their positions are inconsistent with the skewing of the peaks in fig. 3.

When the graph is scaled to match fig. 3 from 0Hz to 15.9kHz, the lower frequency peaks in fig. 3 gradually skew further and further to the left of the peaks of the graph.

However when I add 2F2-8F1 and 2F2-6F1, instead of being to the right of the peaks in fig. 3, they are to the left.

So in spite of the skewing of fig. 3, it's rather evident that the two peaks of interest here are NOT at 2F2-8F1 and 2F2-6F1, but rather are higher in frequency.

Unless of course your math is wrong.

se

Last edited by Steve Eddy; 7th September 2009 at 03:50 PM.

 7th September 2009, 04:18 PM #1046 diyAudio Member     Join Date: Sep 2002 Location: Sacramento, CA By the way, when I made the graph, I did so assuming that the leftmost point on the X axis in fig. 3 was 0. I got to thinking that may have not been a good assumption. So I've since scaled the graph between 0.9kHz and 15.9kHz and that gives a near perfect fit and it appears that the leftmost point in fig. 3 is 20Hz. Now that the graph is properly scaled, I can get a much better estimation of the frequencies of the two peaks in question, and they're at approximately 5kHz and 11.3kHz. se
 7th September 2009, 05:57 PM #1047 diyAudio Member   Join Date: Jul 2003 Location: berkeley ca Thanks Steve, and if the frequencies don't fit, we have to look elsewhere for the cause. How about FM modulation?
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Join Date: Sep 2002
Location: Sacramento, CA
Quote:
 Originally Posted by john curl Thanks Steve, and if the frequencies don't fit, we have to look elsewhere for the cause.
Or as the late Johnnie Cochran might have said, "if the frequencies don't fit, you must acquit."

Quote:
I'll let y'all fight over that one. I just wanted to try and get to the bottom of what exactly was represented in fig. 3.

se

 7th September 2009, 06:23 PM #1049 diyAudio Member   Join Date: Jul 2003 Location: berkeley ca That's fair, and I couldn't spell 'acquit' so I left it out. I did note that the unknown frequencies (at least 4) appear to be symmetrical about the fundamental and the 3'rd harmonic, respectively.
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Join Date: May 2002
Location: Great City of Turnhout, Belgium
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Quote:
 Originally Posted by Steve Eddy Or as the late Johnnie Cochran might have said, "if the frequencies don't fit, you must acquit." I'll let y'all fight over that one. I just wanted to try and get to the bottom of what exactly was represented in fig. 3. se
Steve, I had an appointment with Jan Lohstroh today and took the opportunity to go through his files from way back. Came up with this:

http://www.linearaudio.nl/Miscellane...poo%201976.pdf

I haven't gone through it in detail, just scanned and posted it, but it does offer some other perspectives on the DIM method and results.

jd
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