Class i discussed here by Kendall Caster-Perry:-
The Class i low-distortion audio output stage (Part 2) | EDN
Main benefit is a 'purely resistive' output impeadance. Includes a formal analysis of the circuit - might be an interesting one to explore in a future design, but I dont know it it is suitable for really high powers.
The Class i low-distortion audio output stage (Part 2) | EDN
Main benefit is a 'purely resistive' output impeadance. Includes a formal analysis of the circuit - might be an interesting one to explore in a future design, but I dont know it it is suitable for really high powers.
The article goes into the theory but does not present much by way of an actual circuit.
Part one does present the following as a starting point:
http://www.edn.com/design/consumer/...roduction--the-problem-with-push-pull-outputs
Putting the theory into practice would be a significant effort.When do we get started?
Part one does present the following as a starting point:
An externally hosted image should be here but it was not working when we last tested it.
http://www.edn.com/design/consumer/...roduction--the-problem-with-push-pull-outputs
Putting the theory into practice would be a significant effort.When do we get started?
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There is other thread about Class i and siblings http://www.diyaudio.com/forums/solid-state/202684-class-i-siblings.html
Main benefit ???
Hi Andrew,
It's not as 'purely resistive' as you might think, rather it is Zo + Re, where Zo is about the output impedance of any other (regular) EC OPS. Moreover, we have two Re's, the top and the bottom one. If they aren't exactly equal they create another source of distortion (except in case of class-A operation, of course). I wouldn't see this as 'beneficial' feature of class-I.
See: http://www.diyaudio.com/forums/solid-state/202684-class-i-siblings.html#post2826537
and also: http://www.diyaudio.com/forums/solid-state/202684-class-i-siblings-14.html#post2852220
Cheers,
E.
Hi Andrew,
It's not as 'purely resistive' as you might think, rather it is Zo + Re, where Zo is about the output impedance of any other (regular) EC OPS. Moreover, we have two Re's, the top and the bottom one. If they aren't exactly equal they create another source of distortion (except in case of class-A operation, of course). I wouldn't see this as 'beneficial' feature of class-I.
See: http://www.diyaudio.com/forums/solid-state/202684-class-i-siblings.html#post2826537
and also: http://www.diyaudio.com/forums/solid-state/202684-class-i-siblings-14.html#post2852220
Cheers,
E.
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We've seen very low distortion available from ClassAB for a long time now - why would Class i be of any interest other than intellectual ?
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The article claims low distortion before closing the loop. Is it attractive?
Hi Guys
Anything that reduces let alone eliminates crossover distortion is worth investigation.
However, a traditional output stage with a simple bias regulator that monitors output current is a simpler solution, requiring just a two-BJT regulator. Idle current is rock solid and fairly easy to set by selecting Re for the outputs. The downside with this simple approach is that Vq must be one Vbe drop - or two - where class-i and Doug Self's class-A bias servo (three BJTs plus two current sources) both allow a Vq that is quite low, accommodating low Re values.
If you follow the links to the article and read the three parts available, you'll see that device matching is important in class-i.
Have fun
Kevin O'Connor
Anything that reduces let alone eliminates crossover distortion is worth investigation.
However, a traditional output stage with a simple bias regulator that monitors output current is a simpler solution, requiring just a two-BJT regulator. Idle current is rock solid and fairly easy to set by selecting Re for the outputs. The downside with this simple approach is that Vq must be one Vbe drop - or two - where class-i and Doug Self's class-A bias servo (three BJTs plus two current sources) both allow a Vq that is quite low, accommodating low Re values.
If you follow the links to the article and read the three parts available, you'll see that device matching is important in class-i.
Have fun
Kevin O'Connor
Just for fun look up the Musical Fidelity A1, namely the output stage... so this has been done before, quite a long time ago, actually. There is also a better way of supplying the bias voltage, by injecting a small surrent into the feedback node. Then the input side of the differentials can be simply connected together (A1 connects only for AC using one coupling cap per side but this can be simplified to a straight-through DC connection).
Yes, for a number of reasons, one of which was deliberately low diff stage gain. But, if you look at it, it's exactly the same approach as here, except the bias offset voltage is added on the feedback end.
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