Power Amp Front End with integr. OpAmp and Signal Pad by Power Supply Rail - Naming?

There are some commercial and diy power amplifier with an operational amplifier as front end.
At some of them the signal pad comes from the regular OP-AMP output.
But there are a second kind of signal out.
In this case the normal output from OP-AMP goes of GND (resistor between 100R and 1K) and the signal comes from the positive and negative PIN for the voltage supply.
What is the colloquial term of this topology and what are the pros and cons? (in post #4 one will find the right information).

I need this information to find appropriate design rules for such a front end on the web.
I asume, that the rules for replace the OP through a better version from currently production (like the LME series from NS resp. TI are not the same compare to cases, where the signal pad goes about the normal output.
Who can call me the term for this topology? Thank you for this information.
Here is a good description of this topology:
https://www.analog.com/media/en/tec...tes/58052492001115525484056221917334AN211.pdf
 
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I first saw the idea of using the opamp power pins as signal outputs in National Semiconductor's Application Note AN29, "IC Op Amp Beats FET's on Input Current", published in 1969. See Figure 30. The same circuit shows up in National's AN31, "Op Amp Circuit Collection", on page 16, labeled as "Power Booster".

A more recent example is shown in Mark Alexander's current-feedback power amplifier design (circa 1990). The Ap Note was first published by Precision Monolithics (PMI) but Analog Devices has a readable photocopy (some of the diagrams are a little smeared) on their web site. He also presented a somewhat more comprehensive paper at an Audio Engineering Society convention - you may be lucky enough to find a copy of the convention procedings in a university library.

Alexander's topology has been discussed in several places - seed a search engine with "Alexander current feedback amplifier". One (of several) threads on this Forum is http://www.diyaudio.com/forums/solid-state/108791-alexander-amp-current-feedback-opamps.html .

I don't recall any particular name for a circuit using the opamp supply pins as signal outputs. It's an easy way to do a single-ended-to-differential conversion. The circuit you showed, as well as Alexander's amp, use a transistor to directly sense the supply current and then use the current, rather than a voltage, as the signal so it might be called something like "current coupled amplifier" or "current steered amplifier".

Two design considerations come to mind. The first is that the opamp's quiescent current will appear as part of the output signal current. This may simplify, or may complicate, the problem of biasing later stages. The second problem is that the opamp's two supply currents probably do not flow for the full waveform cycle, since the opamp output stage probably operates in class AB or class B.

Dale
 
I first saw the idea of using the opamp power pins as signal outputs in National Semiconductor's Application Note AN29, "IC Op Amp Beats FET's on Input Current", published in 1969. See Figure 30. The same circuit shows up in National's AN31, "Op Amp Circuit Collection", on page 16, labeled as "Power Booster".

A more recent example is shown in Mark Alexander's current-feedback power amplifier design (circa 1990). The Ap Note was first published by Precision Monolithics (PMI) but Analog Devices has a readable photocopy (some of the diagrams are a little smeared) on their web site. He also presented a somewhat more comprehensive paper at an Audio Engineering Society convention - you may be lucky enough to find a copy of the convention procedings in a university library.

Alexander's topology has been discussed in several places - seed a search engine with "Alexander current feedback amplifier". One (of several) threads on this Forum is http://www.diyaudio.com/forums/solid-state/108791-alexander-amp-current-feedback-opamps.html .

I don't recall any particular name for a circuit using the opamp supply pins as signal outputs. It's an easy way to do a single-ended-to-differential conversion. The circuit you showed, as well as Alexander's amp, use a transistor to directly sense the supply current and then use the current, rather than a voltage, as the signal so it might be called something like "current coupled amplifier" or "current steered amplifier".

Two design considerations come to mind. The first is that the opamp's quiescent current will appear as part of the output signal current. This may simplify, or may complicate, the problem of biasing later stages. The second problem is that the opamp's two supply currents probably do not flow for the full waveform cycle, since the opamp output stage probably operates in class AB or class B.

Dale
Good advices and informations - thank you very much therefore. Do you know about the thread here on diyaudio, where are discussed the pros and cons in cases, where the signal pad goes about the voltage supply pins and the normal output pin as second solution ?
 
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You all missed the latest , greatest Alexander based amp.
http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-99.html#post4110623

Member still4given built it without trying different op-amps and getting the
current right - he finally got the current right in a later post and was pleased.
another member (Thimios) built it and tested it , even.
http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-144.html#post4326318

They run it with the "no BS" 300W slewmaster. (below)
Apex audio has the A9 amp that also uses this topology.

Don't bother with those 20th century designs or Rod Elliot 20'th century assessment.
Eyesee and apex A9 work at overload , any op-amp , and output stage.
This design has been "aced" !

Edit - hard to find with such a long thread , but (below 2) is the perfect Alexander IPS.
OS
 

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Here is a bit more information on this kind of amplifier:
Elliott Sound Products - Audio Power Amplifier Design Guidelines

Got to the bottom to see what he thinks.
URL is death. But still available, either archived under
Elliott Sound Products - Audio Power Amplifier Design Guidelines
or the new currently URL
Elliott Sound Products - Audio Power Amplifier Design Guidelines - go to
"9 Designs to Avoid" - Figure 16.
Mr. Rod Elliott and the author of this paper under
https://www.analog.com/media/en/tec...tes/58052492001115525484056221917334AN211.pdf
have a different view here
 
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In this case the normal output from OP-AMP goes of GND (resistor between 100R and 1K) and the signal comes from the positive and negative PIN for the voltage supply.
What is the colloquial term of this topology
Well its voltage-in current-out so its a form of transconductance stage with balanced output. The output currents are usually fed through common-base stages to achieve better voltage compliance and allow the opamp to be decoupled normally.