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Old 18th May 2012, 02:05 PM   #641
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Correct.
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Old 18th May 2012, 02:27 PM   #642
AndrewT is offline AndrewT  Scotland
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Where does this myth (that ClassA = constant supply current) come from?
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Old 18th May 2012, 02:39 PM   #643
FdW is offline FdW  Netherlands
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Quote:
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Where does this myth (that ClassA = constant supply current) come from?
I think it was 'Myth Busters', the myth was not 'Busted' True-class-A uses constant current (more or less). Some not-so-true-class-A modes vary the supply current, the judges are still out (if this is class-A or not).
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Old 18th May 2012, 03:00 PM   #644
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Contant current most of the time.....
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Old 18th May 2012, 04:37 PM   #645
AndrewT is offline AndrewT  Scotland
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ClassA is not constant supply current.

ClassA is a mode of operation that does not invoke crossover distortion.

Constant supply current is a continuous non varying current flowing from PSU to client circuit.

There are some ClassA topologies that draw a virtually constant supply current. These topologies are far outnumbered by the non constant supply current topologies that are available.

Designers and builders very rarely adopt the few constant supply current ClassA topologies.

Far and away the majority of ClassA circuits, irrespective of whether they are Single Ended, or Push Pull, or dual polarity, or single polarity, that we see are not constant supply current.

The most recent posting I am aware of that discussed this non constant supply current was made by me just yesterday. But there are many Threads discussing this myth and and showing the error in the understanding.
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Last edited by AndrewT; 18th May 2012 at 04:42 PM.
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Old 18th May 2012, 05:02 PM   #646
mikelm is offline mikelm  England
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Quote:
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Where does this myth (that ClassA = constant supply current) come from?
From Class A amps with constant current
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Old 18th May 2012, 05:03 PM   #647
AndrewT is offline AndrewT  Scotland
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How many have you seen posted in this Forum?
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Old 18th May 2012, 05:27 PM   #648
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Ok, before we go deeper i will measure the amp from post 1 ( modified with a CCS ) during music playback ( loud ).
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Old 18th May 2012, 05:32 PM   #649
AndrewT is offline AndrewT  Scotland
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Will you need to add a current measuring sensor into one or other of the supply rails?
0r1 resistor will do the sensor duty.
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Old 18th May 2012, 06:04 PM   #650
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Andrew's observation is absolutely correct. If the supply current was not modulated obviously there would be no voltage developed across the speaker and of course no sound. Even with SE although the load is a constant current, the supply current is not.
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