Very simple class B amplifier

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If you really want an opamp in there, but more voltage swing, try bootstrapping it. See the Audio Analogue Puccini/Donizetti power amp design for a good example
Where have you discocer the schematic?
 

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If you really want an opamp in there, but more voltage swing, try bootstrapping it. See the Audio Analogue Puccini/Donizetti power amp design for a good example

Thanks for the input. A bit of search engine surfing turned up the original article that served as inspiration for the Audio Analogue guys.

Linear1.jpg


This document explains the technique in a very detailed way.

http://www.pi.infn.it/~federico/Immagini/bootstrap.pdf[SIZE=+1]

[/SIZE]For those too impatient to read the article, here is what they came up with:[SIZE=+1]
[/SIZE]
 

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Thanks Ing,
I have seen the "design idea" used in many opamp driven power amps and have seen comment on why it is needed for the higher voltage rails.
That is the first time I have seen an explanation of why the circuit is necessary and a detailed what the circuit does and how to ensure you get out of it what is needed.

Thanks again for searching.

Any chance of posting the missing page?
 
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Thank you for this information.
A similare topology I have found in the magazine "Audio Amateur" 3/96 (THREE: 1996), start from page 22:
"10 Watt Class-A" by Dick Crawford.
Equipped with a dual OP-Amp "LT1124", one pair MOSFET IRFP150/RFH25P08 and an active bias part. Actually not exact matched for this topic, but through the great similarity in the circuit topology I mentioned here.
Perhaps one of the member can scan and upload this article.
 
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An external capacitor gives you a lot more scope. Just for that freedom of choice that I would vote for the NE5534.

If you look at the internal circuits, they are very similar but there are a few small differences between them.
 

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Thanks Ingenues, I am working on a similar design.
I started working with OPA134 then I consider NE553x because of it's +-22volt power supply ability.
With LTspice simulation with NE5534 I can see what happens about the compensation capacitor value about a design of mine close to the one published in this thread.
0pF unstable
10pF unstable
15pF marginaly stable THD 0.0025% @ 20Khz
20pF stable THD 0.003% @ 20Khz
30pF stable THD 0.007%
40pF stable THD 0.015%
60pF stable THD 0.05%
Clearly a THD / stability trade off.

Where can I find NE5534 diagrams giving Gain versus Frequency and Phase versus Frequency at various Cc values ?
 
The there is a bandwidth product that you use.
Bandwidth/ gain = maximum frequency.
I'd like Bode diagrams to study about stability. To find Phase margin and gain margin.
The Gain Bandwith product ( 10 Mhz for the NE553x ) is not the answer about stability margin.
The TI datasheets, I found are giving Gain versus Frequency but no Phase versus Frequency. Both are needed to find stability margin.
 
An external capacitor gives you a lot more scope. Just for that freedom of choice that I would vote for the NE5534.

If you look at the internal circuits, they are very similar but there are a few small differences between them.

Would be more accurate to compare them within a single manufacturer.
The first sch is from TI and the second one from Phillips and it s likely
that they use these schematics even for the other variant.
 
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