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Old 20th September 2012, 09:02 PM   #1091
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I made new my schem.

This amp has good performance characteristics and rail to rail input and output.
amp works from +/-7v
Amp delivers 3 Vrms of out with thd lower then 0,001%

Pot R1 - dc offset nulling
Resistor R3 change quiescent current of the output stage.

schem:
Click the image to open in full size.

Last edited by stridervvv; 20th September 2012 at 09:06 PM.
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Old 20th September 2012, 09:25 PM   #1092
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by ChocoHolic View Post
Would it bring enough gain to keep Id of the JFets unmodulated?
But agreed, let's elaborate on this in bcarso's special thread.
Definitely also interested in this.

..and I have to apologize to RNMarsh (and other DC contributors) for my rough words earlier, I agree that DC and thermal stability must not be ignored - just had the feeling that we had put to much efforts on that, while not discussing the AC topics!
Since reading the last pages I feel more on an audiophile track again. Thanks to all for that.
No problem-o Thx for saying so. Fortunately I have pretty thick skin. Now we are friends again :-) -RNMarsh
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Old 20th September 2012, 09:34 PM   #1093
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Choco, the bias of the folded cacode could also be referenced to the input stage on top of the transdiode. I would then make the voltgae over the output Fet higher and a string of Leds could do that. Sorry, this may be off totic but i have not seen that bcarso has opened that road until now.
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Old 20th September 2012, 09:35 PM   #1094
RNMarsh is offline RNMarsh  United States
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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? Are we back to that so quickly? A lot has been studied and tested and written about. yet we keep doing single tone tests. If multi-tones aint it...Can we get suggestions for a more complete set of tests that are meaningful for our SOTA opamp being designed here? There's designing it and there is testing it. How will we know it is really better than a simpler circuit or something else? -RNmarsh

Last edited by RNMarsh; 20th September 2012 at 09:41 PM. Reason: the circuit and the testing of it -
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Old 20th September 2012, 09:59 PM   #1095
bcarso is offline bcarso  United States
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Quote:
Originally Posted by ChocoHolic View Post
Would it bring enough gain to keep Id of the JFets unmodulated?
But agreed, let's elaborate on this in bcarso's special thread.
Definitely also interested in this.
I'll try to get to this soon, but don't wait for me --- I will be pleased if anyone jumps in and starts it. I am easily distracted

I will say that after a cursory review of two patents I was kindly sent, I think that at least one aspect of linuxguru's basic approach, namely the nearly constant operating point of the main device, both current and voltage, is not covered per se.
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Old 20th September 2012, 10:00 PM   #1096
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Originally Posted by RNMarsh View Post
friends again :-)


Quote:
Originally Posted by Joachim Gerhard View Post
Choco, the bias of the folded cacode could also be referenced to the input stage on top of the transdiode.
...now I have to think again - difficult after a day that drove my brain in sort of a synaptic collaps.
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Old 20th September 2012, 10:46 PM   #1097
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That is the perfect starting point !
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Old 20th September 2012, 10:55 PM   #1098
SY is offline SY  United States
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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? ...Can we get suggestions for a more complete set of tests that are meaningful for our SOTA opamp being designed here?
No need to be Manichean. Lots of good test signals out there.

The fundamental problem to me is that no-one has agreed on an actual, specific design goal. Vague target means that the conversation wanders all over the place and nothing definitive will ever come out of it.
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Old 20th September 2012, 11:03 PM   #1099
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I use dynamic measurements with very high resolution all the time. I had a lot of hope to find a correlation to audible quality. Curious enough the designs that had very low harmonic distortion measured the conventional way with single tone up to 10kHz also scored best on the dynamic tests. For example an AD797 scores great with gain up to x10 challenging my equipment. Can i build a better sounding line stage with gain of x10 compared to an AD797 with the same gain ? You bet, but why ? Added distortion that makes the sound "fuller" or more "natural" ? I do not think so, i can not hear better then -60dB, low order, and my line stage is much better at around -100dB THD.
See an old post from 2009 on my MPP thread. That was the time i measured much but i have given up.
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Old 20th September 2012, 11:08 PM   #1100
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by SY View Post
And how do you fit 20,000 different tones into the audible bandwidth and still be able to see any harmonics
Harmonics will not be seen. The idea is that noise will increase. But how this
noise will be measured in the presense of such a big population of main tones?

But new relevant methods are already proposed :

Quote:
When the number of tones increases, the distortion
products gradually merge into a continuum and
approach the result obtained with noise. Beyond a
certain density of tones the distortion spectrum of
multitone and noise are almost identical
...
With this technique we can use any complex test
signal such as music or speech at realistic levels and
measure the non-coherent distortion. Ultimately, is
this not what everyone wants to do?!
http://www.listeninc.com/PDFs/paper_...Listen_Inc.pdf

In any case, for an amateur , the two or three tone tests conducted at various levels and with a real load connected at the output are still OK.
The resulting new frequencies all fall within the audio band, most of them within the ear’s most sensitive band (1-3Khz)

Two tones: The 19 kHz and 20 kHz equal-level sine waves test
Three tones: The 20.00 kHz, 10.05 kHz, and 9.00 kHz equal-level sine waves test

From Bob Cordell book, CHAPTER 22 “Distortion and Its Measurement

George
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