Modular Preamplifier with IC Class A (SAM Electronic Circuits) - diyAudio
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Old 12th October 2012, 10:39 AM   #1
maouna is offline maouna  Greece
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Default Modular Preamplifier with IC Class A (SAM Electronic Circuits)

Hello.Has anyone tested this preamp? How it sounds?

Class A ampIC
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Old 12th October 2012, 02:33 PM   #2
AndrewT is offline AndrewT  Scotland
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I doubt the claim.

Do you know what the maximum ClassA current of the IC is?

Do you know what drive this level of ClassA output current can achieve?
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regards Andrew T.
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Old 12th October 2012, 11:07 PM   #3
maouna is offline maouna  Greece
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I didnt understand your question.Can you explain?

Transistors Q1 and Q2 are biased at about 9.9mA.They dissipate about 150mW. Class-A amplifier have an efficiency of about 25%. So the preamp's output power is about 37mW maximum.

I want to use it with Rod Elliot's P3A amplifier,not with earphones.

Last edited by maouna; 12th October 2012 at 11:09 PM.
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Old 13th October 2012, 10:35 AM   #4
maouna is offline maouna  Greece
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Would it be better if a filter at the input was implemented?
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Old 13th October 2012, 11:38 AM   #5
AndrewT is offline AndrewT  Scotland
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The ClassA limit is more likely to be set by the IC.
Its ClassAB output is limited to around 40mA.
But it's ClassA maximum current will be set by the bias of the output stage inside the IC.
That (push/pull) ClassA maximum current could be 2mApk, or 1mApk, or 500uApk or any other tiny value that you have no control over.

If the output stage draws more than the IC ClassA peak current limit then the IC transitions over to ClassAB. i.e. the amp is no longer in ClassA.

So my questions
Quote:
Do you know what the maximum ClassA current of the IC is?

Do you know what drive this level of ClassA output current can achieve?
remain to be answered.

There are some websites and some are linked from this Forum, that can change the IC to a single ended ClassA output stage. That topology could be used to ensure ClassA operation for a designed and useful level.

The sch you have shown cannot work in ClassA to any significant nor useful level.

I repeat my first statement
Quote:
I doubt the claim.
do your homework.
Learn to understand what is proposed.
Learn to discard the rubbish that is all too often repeated on the web, i.e. sort the wheat from the chaff.
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regards Andrew T.

Last edited by AndrewT; 13th October 2012 at 11:43 AM.
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Old 13th October 2012, 02:45 PM   #6
maouna is offline maouna  Greece
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I think i understand this now.i did some research and this is what i found :

Class A operation requires that the output transistors be biased such that the quiescent collector current is equal to the peak current demanded by the load.If more current is demanded then the output transitions to Class AB.
To change the IC to a single ended Class A output stage,a current source from one rail to the output pin of the opamp, that can be a resistor, bipolar transistor, a jfet or a current source,is needed.
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