John Curl's Blowtorch preamplifier part II - Page 103

stinius · 6th September 2009, 08:37 PM

What about letting this discussion rest for a while and find a new topic?

At the moment we are all done and need a break. It’s a very interesting topic so I’m sure (and hope) it will be back on the arena within a couple weeks.

I hope that’s ok by you as well John.

Cheers

Wavebourn · 6th September 2009, 09:07 PM

The keyword is asymmetry of sidebands. John said that finally.

It reminds me an old story about one professor: "They are dumb! I've explained them, but they did not understand! I explained them once more, but they did not understand! I explained the third time; I even myself understood, but they still did not!!! How dumb they are?!"

john curl · 6th September 2009, 09:34 PM

Thank you, Wavebourn.

john curl · 09:52 PM

Stinius, everyone wants to 'bail' but not yet. We have to look at which it is: Matti's or Mitch's explanation that is ACTUALLY being measured?
i.e. is it IM or FM(or AM) that is showing up on the graph? It's easy, just do the math yourself and try to fit it to the graph. Rough fits are NOT OK.

gerhard · 6th September 2009, 09:44 PM

Quote:

Originally Posted by Wavebourn

The keyword is asymmetry of sidebands. John said that finally.

It reminds me an old story about one professor: "They are dumb! I've explained them, but they did not understand! I explained them once more, but they did not understand! I explained the third time; I even myself understood, but they still did not!!! How dumb they are?!"

I heard that Buddha said most people need _many_ explanations how to
achieve nirvana; very wise men would need only abt. 50000.

Is this an acceptable input voltage for the amplifier test?

Steve Eddy · 6th September 2009, 10:22 PM

Quote:

Originally Posted by john curl

i.e. is it IM or FM(or AM) that is showing up on the graph? It's easy, just do the math yourself and try to fit it to the graph. Rough fits are NOT OK.

Rough fit's all you're going to get.

The graph doesn't even fit its own numbers.

I created a simple graph using the numbers given but it doesn't scale so as to fit the published graph.

se

gerhard · 6th September 2009, 10:22 PM

reconstructed test circuit.
The second stage was necessary because the 5K load requirement
prevented getting enough signal into the 50 Ohm spectrum analyzer.
Its influence should be negligible.

gerhard · 6th September 2009, 10:51 PM

I hate this Canon PowerShot Pro!!!11!!!

The spectrum is close to the one in the paper.
Sorry, I have abused a RF spectrum analyzer.

1audio · 6th September 2009, 11:05 PM

Gerhard:
Is that the input or the output of the opamps? Or is there an input sensitivity issue preventing looking directly at the input?

gerhard · 6th September 2009, 11:21 PM

That's the output of the Lt1028.
I could loook at the first op amp with a Tektronix FET probe,
but that has probably to much IMD.

BTW R7 was intended to be 1K only but I won't change this again.

The peaks are at

1.370 KHz
2.270 KHz
3.180 KHz (center)
4.080 KHz
4.990 KHz

(by moving the crosshair cursor)

6th September 2009, 09:38 PM	#1024
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Stinius, everyone wants to 'bail' but not yet. We have to look at which it is: Matti's or Mitch's explanation that is ACTUALLY being measured? i.e. is it IM or FM(or AM) that is showing up on the graph? It's easy, just do the math yourself and try to fit it to the graph. Rough fits are NOT OK. Last edited by john curl; 6th September 2009 at 09:52 PM.

6th September 2009, 11:05 PM	#1029
1audio diyAudio Member Join Date: Mar 2004 Location: SF Bay Area Blog Entries: 2	Gerhard: Is that the input or the output of the opamps? Or is there an input sensitivity issue preventing looking directly at the input? __________________ Demian Martin Product Design Services

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6th September 2009, 08:37 PM	#1021
stinius diyAudio Member Join Date: Oct 2008	What about letting this discussion rest for a while and find a new topic? At the moment we are all done and need a break. It’s a very interesting topic so I’m sure (and hope) it will be back on the arena within a couple weeks. I hope that’s ok by you as well John. Cheers

6th September 2009, 09:07 PM	#1022
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	The keyword is asymmetry of sidebands. John said that finally. It reminds me an old story about one professor: "They are dumb! I've explained them, but they did not understand! I explained them once more, but they did not understand! I explained the third time; I even myself understood, but they still did not!!! How dumb they are?!"

6th September 2009, 09:34 PM	#1023
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Thank you, Wavebourn.

6th September 2009, 11:21 PM	#1030
gerhard diyAudio Member Join Date: Oct 2005 Location: near Stuttgart, south Germany	That's the output of the Lt1028. I could loook at the first op amp with a Tektronix FET probe, but that has probably to much IMD. BTW R7 was intended to be 1K only but I won't change this again. The peaks are at 1.370 KHz 2.270 KHz 3.180 KHz (center) 4.080 KHz 4.990 KHz (by moving the crosshair cursor)