Power Amplifier with Small Signal OP-Amp in the Front-End - Overview wanted

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#21
mt490 said:
Two to add to the second category:

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I recently researched these two approaches to come to the amplifier I am playing with now.

I came to the conclusion to build an amplifier of the second type, with ADA4700-1 and CFP buffer mutated towards CFA (similar to SSA-35 approach, but different feedback connection to maintain stable bias without thermistor).

My own observations were: Alexander topology (an amplifier of the first kind) is both more flexible and less flexible at the same time. Effects of thermal and SOA management functions common in modern opamps but not shown in simplified circuits are difficult to predict without actual tests. Some key parameters such as PSRR can be degraded and and stabilisation is potentially non-trivial. But at the same time you can use a higher variety of opamps as well as manipulate feedback factor much more intricately.

Putting together something of the second topology is far more trivial, but you do not have a whole lot of options for the front end when it comes to rails above 18V. OPA445, OPA552, LTC6090 and of course the ADA4700-1 that I used, are some that are in current production. You could also consider the phased out LME49810/11/30 to be types of front end too. The common theme for downsides being the restricted slew rates.

For me the ADA4700-1 appeared to me to have the best balance of performance over the competitors I considered. It doesn't leave much room to move though being unity gain compensated, but my purposes fit inside the envelope.
Click to expand...
URL is dead - go to
https://web.archive.org/web/20140221221337/https://www.by-rutgers.nl/SSA-30W.html
https://by-rutgers.nl/PDFiles/Amps/SSA35.pdf
In the attachment the simplified schematic of Germans no longer exist brand "Fidelity" model "TOPAS"
 

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#23
You could copy the diyAudio FirstWatt "IPS7" idea of providing TWO sockets for each opamp on the PCB. Now experimenters and DIYers and "op amp rollers" can use EITHER a single opamp chip OR a dual opamp chip, at every position.

Some really excellent opamps are ONLY available as singles (LT1122, AD825, OPA604, etc.) and other really excellent opamps are ONLY available as duals (LM4562, OPA1656, LT1498, etc.) Now your PCB can accommodate them all!. Maybe you will discover that your ears prefer an unexpected blend of some Single opamps HERE, and other Dual opamps THERE. You've made this kind of experiment possible! Congratulations!!


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#24
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#25
#29
more topologies with op-amp as input stage:
lineup

Thread 'OpAmp as Input in Power Amplifier - exploration'

This thread is about all ways to use OpAmp as input stage in power amplifiers.
Let us see your way to do this.
There are many ways to make an opamp control a power amplifier.
There are good ways, I am sure - and less good ways.

I have one way up my sleeve now, but I also have Choctaw in another thread.
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