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Old 23rd August 2012, 10:31 PM   #121
bcarso is offline bcarso  United States
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By exploiting the use of floating power supplies, to which EUVL has gotten me momentarily addicted after I started looking at his IV threads, and with RM's allowance for cascodes and current sources not counting, I have a crazy design for the opamp that uses six transistors. But two to four floating voltage sources (one to three of which could be primary batteries as there is virtually no current), a very asymmetrical-looking input stage... If all one needs is an inverting input the thing gets much simpler and the floating V source that actually supplies real current goes away.

When I have convinced myself I understand it I'll present it. It does use the buffer I showed, and counts that as four devices (the two current sources being exempt).

Of course I'm not doing this to meet the eight transistor limit, but I'm amused that it may be possible. I don't believe it will sound better on account of the lower number.
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Old 23rd August 2012, 10:38 PM   #122
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Originally Posted by bear View Post
I think this may illustrate somewhat:

Anyone built this power Diamond Buffer amp ?
.....

I am led to believe that this is Chris Paul's work, and was perhaps published in a mid 80s (?) audio amateur if not elsewhere....
I think this particular one (LEDs in current sources) is Walt Jung's creation:

http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_2.pdf
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Old 23rd August 2012, 10:40 PM   #123
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The best "sounding" amp you can get from 2 transistors, if don't count active loads. More is worse, but may be needed for convenience. If it has to be symmetric it needs 2 more transistors. But if you demand differential input of course it is not enough to have 4 transistors, but it has nothing to do with the sound quality, rather with convenience of usage.

That's why I asked from the beginning, what do we want: an audio amp, or an opamp.

Also, divisions on "VAS" and "Output buffer" are needed not for the amp, but for convenience of it's design.

One more thing: local feedbacks, limited gains of stages, are preferred if you design an amp. However, if you design a building block of active filters, servos, or similar stuff, you probably need higher gain.
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Old 23rd August 2012, 10:43 PM   #124
bcarso is offline bcarso  United States
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And remember that opamps, as conceived and realized for analog computation, used to only have inverting inputs
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Old 23rd August 2012, 10:48 PM   #125
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Quote:
Originally Posted by bcarso View Post
And remember that opamps, as conceived and realized for analog computation, used to only have inverting inputs
If modern opamps had an inverting input only I would definitely prefer them for audio.
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Old 23rd August 2012, 11:00 PM   #126
bcarso is offline bcarso  United States
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If modern opamps had an inverting input only I would definitely prefer them for audio.
Back when we didn't even have a word for common-mode distortion

At the risk of mentioning something a bit political, that reminds me of Dubya's gaffe, when he said the French didn't even have a word for entrepreneur.
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Old 23rd August 2012, 11:09 PM   #127
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If modern opamps had an inverting input only I would definitely prefer them for audio.
If you ground the + input they do have only a - input.
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Old 23rd August 2012, 11:10 PM   #128
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I once made a mic preamp basically on a single medium power PNP transistor. It was loaded dynamically, of course. But a dynamic mic capsule was effectively between base and emitter, an output transformer effectively between base and collector. It sounded quite nice, but I did not use such trick any more because thought that it was "heresy" and "cheating"
The same, about A+C amp that I thought "heresy" and "cheating", but later in 1980-th discovered that similar topology had been patented as "Current Dumping". The success of it was partly because each stage had own well defined and controlled properties, no "VAS" with "as infinite as possible" voltage gain.
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Old 23rd August 2012, 11:15 PM   #129
RNMarsh is offline RNMarsh  United States
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You should quit 'counting' and start designing. These arbitrary rules are self limiting.
From the Rules as we go along Department -->

If two circuits for a discrete opamp have about the same performance, the one with fewer transistors wins the whole Big Deal; Name up in lights, bragging rights, untold fame and a free trip to beautiful Cool, CA.
probably a movie deal, too.
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Old 23rd August 2012, 11:18 PM   #130
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Originally Posted by hitsware View Post
If you ground the + input they do have only a - input.
No. They still have additions that act as unneeded design constrains making sound worse.

Like, if you don't use motor on your motor-bicycle, why do you need that motor, transmission, fuel tank, frame to support them, that make the bike worse for pedaling?
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