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Old 23rd September 2004, 01:33 AM   #1
cm961 is offline cm961  Canada
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Question Marathon car amp idea current draw

Hi guys,

I'm repairing my brothers car amp for his birthday.

My lab supply maxes out at about 2A output, and the amplifier is triggering the current limiter. I know SMPS draw a lot of idle current. Is it possible that the amp draws more than 2A of current under normal conditions (no input, no output connected)?

For reference, the amplifier is a Marathon USA model US-2100H. From what I can tell, its a pretty high power and high quality unit, but the manufacturer exists no more I believe.

Thanks,
Pete
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Old 23rd September 2004, 01:51 AM   #2
djQUAN is offline djQUAN  Philippines
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most car amps that I have tested (and the one I built) all have around 1A of idle current draw. ranging from 100watts RMS total to a 340watt RMS total car amp. not sure about high power ones though. if they have dual supplies inside, it may have a higher idle current.
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Old 23rd September 2004, 04:11 AM   #3
cm961 is offline cm961  Canada
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I know it has four ultra fast diodes (two devices, each with dual centre taps, NTE6244, NTE6240). But I think its just push-pull type. It uses the 494 PWM controller, is there any pins on it I could check to diagnose something?

Pete
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Old 23rd September 2004, 04:21 AM   #4
cm961 is offline cm961  Canada
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Ok, I just learned that it is a class AB amplifier. I believe class AB draws a lot of idle current does it not? I think I'll put 5A fuses in it and try it from a more powerful supply, but then I can't really monitor current draw.

Any thoughts?
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Old 23rd September 2004, 04:31 PM   #5
djQUAN is offline djQUAN  Philippines
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you could try to see if the output transistors of the amp are blown or shorted.

the TL494, check the pins 9 and 10. they are the output pins.
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Old 23rd September 2004, 05:01 PM   #6
sss is offline sss  Israel
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Quote:
Originally posted by cm961
Ok, I just learned that it is a class AB amplifier. I believe class AB draws a lot of idle current does it not? I think I'll put 5A fuses in it and try it from a more powerful supply, but then I can't really monitor current draw.

Any thoughts?
almost all amps are class ab
i think 2A is too much
dont use more current , u can damage more things
try to find the problem first ,disconnect the power supply from the amp if its possible and test it .
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Old 23rd September 2004, 05:12 PM   #7
djQUAN is offline djQUAN  Philippines
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hmmm. class AB? I have checked all my car amps (well they are low to middle priced ones, I don't have high end stuff) and the emitter resistors of the amp stages don't have any voltage which means they are running at class B operation. a reason why I built myself a dual P3A car amp.
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Old 23rd September 2004, 05:15 PM   #8
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Hi!,

I have had experience with car audio smps not starting on a current limited supply, then seem to need high current for a small time to start. on a current limited supply they just pull the full current without starting up.
Just a though....

James
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