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Old 3rd April 2003, 05:33 PM   #1
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Smile ClassA question for the enlightened...

Hi,

if an amplifier is classA and not single ended, how much idle current is needed ?

Must the idle current trough each transistor be the same or higher then the current through the speaker at all times ?

Or ???
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Old 3rd April 2003, 05:40 PM   #2
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a class A p/p amp can put out 2X the idle current before leaving class A.
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Old 3rd April 2003, 06:55 PM   #3
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p/p ? push/pull ?
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Old 3rd April 2003, 07:44 PM   #4
Bjerre is offline Bjerre  Denmark
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Hi Bernhard

The answer to your question is yes. The idle current must be larger than the largest current ever to go through the load. Said in another way, the idle current must be large enough for the output tubes/transistors newer to turn off.

And yes, p/p is push-pull !
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Old 3rd April 2003, 07:47 PM   #5
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p/p= push/pull
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Old 3rd April 2003, 07:53 PM   #6
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Ok.

I want to built a classA amp, where the idle current increases with the signal.

Does that make sense ?

Some kind of second amp inside the amp which lets the current be high on high signals.
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Old 3rd April 2003, 08:00 PM   #7
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Yes, it makes sense. It has been done before. I can't remember what it was called (there are many here much more knowledgable about that).
What kind of output devices are you using? If you're using MOSFETs, it isn't a good idea, because the low-level resolution will suffer.
Steve
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Old 3rd April 2003, 08:09 PM   #8
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Quote:
What kind of output devices are you using?
Its in Monolithic SuperSymmetry with Current Feedback

I call it madness circuit.
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Old 3rd April 2003, 08:22 PM   #9
Pan is offline Pan  Sweden
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Quote:
Originally posted by nobody special
a class A p/p amp can put out 2X the idle current before leaving class A.
Should be 1x idle right?

Or where do you get the extra current from?

/Peter
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Old 3rd April 2003, 08:47 PM   #10
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Quote:
Should be 1x idle right?
It says 2X idle in the Pass A75 article. That's where I got my info... I think it's correct. Maybe someone can explain why that is. I know I simulated it before, and it made sense, but I can't remember just what happens to explain it better. Sorry.
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