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Old 21st September 2012, 04:01 AM   #1121
benb is offline benb  United States
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It wasn't written by a newbie, it was the late Bob Pease - a guru, though not known as an audio guru:
http://www.ti.com/lit/an/snaa047/snaa047.pdf
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Old 21st September 2012, 04:02 AM   #1122
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
This was not intended as an intellectual exercise in the beginning. After some output stage work I think I can reach (at least) my original goal, a discrete FET input general purpose op-amp with performance as close as possible to the JE990/OPA627/37 when used in the same circuits using almost as few transistors as the JE990 so it fits on a small card. A plus would be an all tiny SMT version.

I would also hope to build and measure a prototype.
OK. Do you have any measured data yet? Or, soon? How is it coming along?

Last edited by RNMarsh; 21st September 2012 at 04:18 AM.
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Old 21st September 2012, 05:58 AM   #1123
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Quote:
Originally Posted by bcarso View Post
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.
Cool - however, it's entirely possible that the topology has been invented earlier. Hopefully, it's not the subject matter of an active patent or continuation. It's fine if it's covered by an expired patent.

Meanwhile, I was temporarily distracted by a gainclone build. I did sim Chocoholic's symmetric CCB, and it works but needs some circuit elaborations.
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Old 21st September 2012, 06:33 AM   #1124
RNMarsh is offline RNMarsh  United States
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I bought 25 devices that look interesting -- a pair of n and a pair of P type MOSFETs in a 14dip. They are made by Advanced Linear Devices -- ALD1105 PBL. Has anyone used them before?
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Old 21st September 2012, 06:44 AM   #1125
PMA is offline PMA  Europe
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Quote:
Originally Posted by scott wurcer View Post

EDIT Sorry PMA already said that but let me add that in doing these multitone tests for years the results were always well behaved and for the most part could be predicted by simple IMD testing at an appropriate level.
I agree that multitone tests usually do not reveal much, in case that the object under test is not poorly designed. I assume we really do not need to speak about uA741, all of us knew how poor it was even 35 years ago. The multitone test on a contemporary design just copies abilities of the measuring device. I agree that CCIF IM 2-tone test may reveal more. Again, it is not difficult today to design an audio component that is very difficult to measure regarding non-linear distortions. So probably we might like to spend our efforts to parameters like high frequency PSRR, RFI immunity, immunity to HF demodulation and detection. This needs high speed design and fulfillment of HF circuits design rules. Together with suppression of LF noises by proper wiring and PCB design inside the housing. Not so easy to get and impossible to get by web discussions.
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File Type: png AMP2 multitone test.PNG (68.8 KB, 239 views)
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Old 21st September 2012, 07:12 AM   #1126
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For those who are not familiar with multitone time plot, please find it attached below.
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Old 21st September 2012, 10:27 AM   #1127
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by Joachim Gerhard View Post
George, the measurements are explained in post 1099

I meant the FFT at post #1107. Is it sine-square superposition? If so, what is the freq of square and sinus input and amplitude ratios?

Thank


Quote:
Originally Posted by PMA View Post
Not so easy to get and impossible to get by web discussions.
He, he. True.

Itís good that you take a short brake from planning/soldering and drop some wise thoughts/suggestions here.

Ref. Attached screenshot
I see the noise floor becoming thicker with freq. increasing. Is it due to the accumulation of intermod products of the multitone test?

George
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Old 21st September 2012, 11:16 AM   #1128
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Here is how that measurement works :
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File Type: png sine-square.png (106.8 KB, 211 views)
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Old 21st September 2012, 01:16 PM   #1129
PMA is offline PMA  Europe
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Quote:
Originally Posted by gpapag View Post

Ref. Attached screenshot
I see the noise floor becoming thicker with freq. increasing. Is it due to the accumulation of intermod products of the multitone test?

George
Hi George,

no. Depends on SW used, type of averaging etc. If I used another SW, you would see "thin" FFT bottom.

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Old 21st September 2012, 01:21 PM   #1130
PMA is offline PMA  Europe
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Quote:
Originally Posted by Joachim Gerhard View Post
Here is how that measurement works :
Hi Joachym,

yes, sometimes we may see something in a DIM/TIM test.

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