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Samuel Groner's super opamp
Samuel Groner's super opamp
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Old 21st May 2019, 03:05 PM   #151
jan.didden is offline jan.didden  Europe
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Absolutely.
Like your sig!
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Old 21st May 2019, 03:12 PM   #152
Bonsai is offline Bonsai  Europe
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Looking at ways to improve my new NEC player i ran into these Technics schematics i was never aware of.Could you tell me more about these composite op-amps circuits? I don't have a clear understanding of what they do right now.
There's an app note somewhere (TI - Ray Mancinni - or was it or BB?) that shows a similar technique - kind of like 'load bootstrapping' so the second opamp takes the load while the first sees almost none and the result is very low distortion.

Looks quite neat.
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Old 21st May 2019, 03:15 PM   #153
Bonsai is offline Bonsai  Europe
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I have used 'AFEC'.

Perhaps not as spectacular as Syn08's RF AF amplifier or the brute force composite approach, but it gets me below the QA401 noise floor.

Augmented Feedback Error Correction (AFEC)
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Old 21st May 2019, 03:39 PM   #154
dreamth is offline dreamth  Romania
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Originally Posted by Bonsai View Post
I have used 'AFEC'.

Perhaps not as spectacular as Syn08's RF AF amplifier or the brute force composite approach, but it gets me below the QA401 noise floor.

Augmented Feedback Error Correction (AFEC)
They already use two of the best op-amps ever made ...i can hardly believe you'd need a more advanced topology for lm4562 or lt1056 than the datasheet provide to get a good sound.
If you can get 85..90 db THD and IMD in all electronic audio chain that is all you need from a technical point of view..From that point on you better look for better speakers...
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Old 21st May 2019, 05:09 PM   #155
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There may be better ways, but this is all I know ;-)

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Old 22nd May 2019, 04:49 AM   #156
PRR is online now PRR  United States
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Originally Posted by dreamth View Post
... these composite op-amps circuits?...
The technicsslp777headphonesamp-png parallels two 50mA opamps to make a 100mA opamp to drive headphones. The booster runs at small gain. Why? Only the designer knows. These are not super-spiffy opamps (big-die '741s) and maybe by using two 15-cent opamps he got the performance of a 50-cent opamp.
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Old 22nd May 2019, 05:14 AM   #157
dreamth is offline dreamth  Romania
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The technicsslp777headphonesamp-png parallels two 50mA opamps to make a 100mA opamp to drive headphones. The booster runs at small gain. Why? Only the designer knows. These are not super-spiffy opamps (big-die '741s) and maybe by using two 15-cent op-amps he got the performance of a 50-cent opamp.
On the contrary and this is what i emphasized a few pages back, which is that the composite op-amps are actually needed to be part of what the Burr Brown app note already said: the "BEST of BOTH WORLDS" for best results, otherwise you can find singular op-amps that can do the job :


You deliberately chose slp777 out of slp990 and slp999 maybe, where they use njm4556s and m5238 for all the positions.NJM4556S isn't the same thing with njm4556D as it has one more ground pin which internally forms also a cooler for the die.So yes, there were op-amps with ground too in the 80's!



M5238 wasn't cheap, still isn't cheap as second hand and still is one of the best op-amp made for audio.He was used in top-end commercial units ad still is great value along with its bipolar brother in arms M5220 which wasn't cheaper than m5219, which again wasn't cheaper than m5218...I think that some Japanese chips set the bar very high for real world performance at the time.

You have also the 741 internal guts...
You know...Japanese datasheet were very scarce compared with their American counterpart but they made wonderful parts which in real life are really difficult to beat in terms of overall performance unless you want to spend a lot of money to prove otherwise.


By the way, i just asked a friend who happened to have a Technics 990 and he said that although he has about 20 top-end cd players of that era (phillips cd880, cd304(i gave him one) and many others,all moded both on the digital and analog side-he has a PHD in numerical processing and he's also a church organ player so he's my refference when i want an opinion, the Technics happens to sound the most accurate.He never had Denons though
I will build that i/v stage of Technics and mod my NEC today just to see if it really makes a difference.I believe it does.
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File Type: png m5238.png (126.3 KB, 383 views)
File Type: png ua741.png (243.6 KB, 388 views)
File Type: png technics slp990headphones amp.png (180.3 KB, 380 views)

Last edited by dreamth; 22nd May 2019 at 05:34 AM.
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Old 22nd May 2019, 02:21 PM   #158
Bonsai is offline Bonsai  Europe
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Here's the Technics headphone amp.

A2 is the load bootstrap amplifier and makes the headphone load (that's the 68 ohm and the actual headphone impedance) appear very high to A1, the main amplifier. With A1 seeing little or no load, the distortion is concomitantly low.

You could do this with 2 off dual LM4562 - 1 acting as A1 and the other three you parallel and form A2 for theoretical ppb distortion levels. IIRC the LM4562 can cleanly deliver c. 30mA so you will have close to 100mA to drive your headphones.


Its a pretty neat trick in my book!
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Old 22nd May 2019, 03:30 PM   #159
scott wurcer is offline scott wurcer  United States
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Originally Posted by Bonsai View Post

You could do this with 2 off dual LM4562 - 1 acting as A1 and the other three you parallel and form A2 for theoretical ppb distortion levels.

Its a pretty neat trick in my book!
You still have the unloaded THD of the first amp as a gain of ~10 follower (with 12k unbalanced source). I don't see -170dB out of this.
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Old 22nd May 2019, 03:52 PM   #160
Bonsai is offline Bonsai  Europe
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I agree that the -170dB THD is pie in the sky - LTspice fantasy.

If you ran A1 with a heavy load, the distortion would go up significantly, so I would say what this does is deliver the distortion performance of A1 when driving a high load so for a good opamp 1-2ppm. The ppb I mentioned is 'theoretical' of course.

You could tweak this design for improved performance - e.g. lower gain setting resistors (4562/797 easily drive 1k at ppm levels) and maybe run A1 inverting to remove CM distortion etc etc

Last edited by Bonsai; 22nd May 2019 at 03:55 PM.
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