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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 26th February 2013, 06:33 AM   #35881
PMA is offline PMA  Europe
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If 19+20kHz max. dv/dt is considered slow, why not to test at higher frequencies, same method?? My usual test is HF CCIF at 300 + 309kHz. Schematic of the method attached. The test frequencies have to be high, but not much above Fc of the input RC filter.
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File Type: png VF_test_schematic.PNG (14.5 KB, 170 views)
File Type: png VF_intermod_300kHz_AMP2_filter_lin.PNG (42.0 KB, 159 views)

Last edited by PMA; 26th February 2013 at 06:36 AM.
 
Old 26th February 2013, 07:53 AM   #35882
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Old 26th February 2013, 08:24 AM   #35883
Kindhornman is offline Kindhornman  United States
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John Curl's Blowtorch preamplifier part II
Okay John I follow you on this. You answered my question in that you would have to go above the 30khz point in order to stay out of the audio band and still remain flat up to 20Khz. I know that I have to study more about the differences between slew rate and settling time. Thanks for the answers and I am glad that we didn't have any flame wars on this subject. I didn't see the response for some reason earlier or I would have responded earlier to the thread.
 
Old 26th February 2013, 11:48 AM   #35884
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Quote:
Originally Posted by john curl View Post
Like this?
I do not know, I cannot read the tone frequencies. Like this:
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Old 26th February 2013, 12:58 PM   #35885
scott wurcer is offline scott wurcer  United States
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Originally Posted by SY View Post
Try my square wave two speed trick- you'll be surprised. I'll try to dig up and post some scope photos to illustrate this point.
I've tried my 1/3 octave noise test at two speeds too, the stylus can't track the recording even when it stays in the groove. So remind me why this thread has circled again back 35 yr. to talk about why 741's are not good for audio.
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Old 26th February 2013, 01:02 PM   #35886
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John Curl's Blowtorch preamplifier part II
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So remind me why this thread has circled again back 35 yr. to talk about why 741's are not good for audio.
Jethro Tull - Living in the past - YouTube
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Old 26th February 2013, 01:23 PM   #35887
john curl is offline john curl  United States
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PMA, I put up one page of a paper written by B&K in the early '70's. It is a fairly complete paper on TWO TONE DISTORTION, and I thought that you should become aware of it.
In all fairness, most midfi equipment is made with a modified 741 type topology, even today, so while slightly improved, the new devices suffer from much the same distortion generating mechanisms as earlier devices.
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Last edited by john curl; 26th February 2013 at 01:35 PM.
 
Old 26th February 2013, 01:32 PM   #35888
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Here is the article. Unfortunately, it is too long to put up here. Perhaps, PMA, you should get the article, since it is about 2 tone testing, and you are doing that too.
One problem here is that while the questions by others are intelligent, they have already been answered and worked through, long ago. It is like teaching a class, where the students don't know much about the material, rather than discussions among professionals.
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Last edited by john curl; 26th February 2013 at 01:36 PM.
 
Old 26th February 2013, 01:32 PM   #35889
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John Curl's Blowtorch preamplifier part II
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...it suffers from much the same distortion generating mechanisms as earlier devices.
That's the opposite of what you claimed when citing the all-important Quan test.
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Old 26th February 2013, 01:34 PM   #35890
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John Curl's Blowtorch preamplifier part II
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It is like teaching a class, where the students don't know much about the material, rather than discussions among professionals.
We'll all keep staring at the ground and drooling.
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