John Curl's Blowtorch preamplifier part II - Page 1239 - diyAudio
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Old 23rd May 2011, 07:50 AM   #12381
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Quote:
Originally Posted by Nelson Pass View Post
I think you can only make that statement if you have a narrow criterion
by which to judge advantage.

Well, Bruno's article being a technical articles I was assuming that the criterium was a reproduction as free from artifacts and coloration and harmonics and PIM and SID etc as possible. With that criterium, his article stands until other technical arguments refute it. Which, I noted, have not been offered by any of the supposedly heavy hitters here.
I do appreciate that such a criterium is different from, say, listener preference. By the same token, listener preference is just that and cannot be argued with.

jan didden
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Old 23rd May 2011, 01:23 PM   #12382
PMA is offline PMA  Europe
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Now, all kinds of EMI interferences are the highest issue in audio, especially HF interference coupled through power rails.

Fast complementary-differential JFET input circuits with high slew rate and high OLG handle this much better compared to 20V/us single-differential input BJT opamps. That is one of the main reasons why topologies like John Curl's sound so good and are so successful. No THD opamp datasheet plots are going to reveal this.
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Old 23rd May 2011, 01:49 PM   #12383
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Quote:
Originally Posted by PMA View Post
Now, all kinds of EMI interferences are the highest issue in audio, especially HF interference coupled through power rails.

Fast complementary-differential JFET input circuits with high slew rate and high OLG handle this much better compared to 20V/us single-differential input BJT opamps. That is one of the main reasons why topologies like John Curl's sound so good and are so successful. No THD opamp datasheet plots are going to reveal this.
Hi Pavel,
Why fast complementary-differential JFET input circuits with high slew rate and high OLG are more immune to RFI?
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Old 23rd May 2011, 02:01 PM   #12384
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Because there is a negligible dynamic saturation. Dynamic saturation is an issue even for signals that arrive through supply rails.
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Old 23rd May 2011, 02:18 PM   #12385
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Thanks.
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Old 23rd May 2011, 03:10 PM   #12386
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Run the bjt opamp heavily into class a. There will be very little garbage on the rails. Modern opamps (VFA) also have extremely high PSRR. One device I am thinking of is > 90db on both plus and minus rails at 20kHz.
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Old 23rd May 2011, 03:30 PM   #12387
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Or build it like RF equipment, so RF only goes where it is supposed to go. In the case of audio equipment this is nowhere.
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Old 23rd May 2011, 03:50 PM   #12388
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Quote:
Originally Posted by PMA View Post
Now, all kinds of EMI interferences are the highest issue in audio, especially HF interference coupled through power rails.

Fast complementary-differential JFET input circuits with high slew rate and high OLG handle this much better compared to 20V/us single-differential input BJT opamps. That is one of the main reasons why topologies like John Curl's sound so good and are so successful. No THD opamp datasheet plots are going to reveal this.
Pavel,

Although I agree with the issue, there are still folks who make products that perform badly enough, that that is not an issue! I know you assume we are talking about well designed modern products, but somebody will go build the ultimate line filters and still hook it up to poor product and then complain you are wrong.

ES
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Old 23rd May 2011, 03:53 PM   #12389
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Quote:
Originally Posted by janneman View Post
Well, Bruno's article being a technical articles I was assuming that the criterium was a reproduction as free from artifacts and coloration and harmonics and PIM and SID etc as possible. With that criterium, his article stands until other technical arguments refute it. Which, I noted, have not been offered by any of the supposedly heavy hitters here.
I do appreciate that such a criterium is different from, say, listener preference. By the same token, listener preference is just that and cannot be argued with.

jan didden
Jan,

Let me finish my questions.

If I have a second amplifier that has the function Vo = 1000 x ( Vin + .05 Vin exp 2) and set the gain to 10 what is the output?

Now if I set amplifier #2 before amplifier #1 each open loop and set the overall gain to 100 what is the output?

That is the gist of my possible article for Vol. 2, but it seems no one understands it!
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Old 23rd May 2011, 04:07 PM   #12390
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Jan, can you point out to me where Bruno mentioned PIM in his article?
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