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Old 8th January 2012, 07:58 AM   #1
back is offline back  Greece
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Default class D vs class AB current capability.

i see some class AB amps that state some huge current capability.
parasound 3500 120ampere peak.
musical fidelity supercharger 240 ampere peak.
there are more but you see my point.
what is the case if we compare that with 20-30 or even 50 amperes of
class d amps?

thanks in advance.
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Old 8th January 2012, 09:05 AM   #2
trevmar is offline trevmar  United States
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Do you want an amplifier to sound good, or one to charge a car battery.

What earthly use is 120 output amps? Where is it going to go? certainly not into an 8 ohm speaker -- unless it is driven by 960 volts and 115,200 watts
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Old 8th January 2012, 09:44 AM   #3
back is offline back  Greece
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Originally Posted by trevmar View Post
Do you want an amplifier to sound good, or one to charge a car battery.

What earthly use is 120 output amps? Where is it going to go? certainly not into an 8 ohm speaker -- unless it is driven by 960 volts and 115,200 watts
yeah 120A is extreme but what if a speaker dips to 3 or even 2.5ohms?

and are those ratings real?

Last edited by back; 8th January 2012 at 09:49 AM.
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Old 8th January 2012, 09:50 AM   #4
trevmar is offline trevmar  United States
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The maths is simple enough, P = V * I, R = V / I

so a 2.5ohm speaker carrying 120 amps is receiving P = I*I*R, or 36,000 watts.

There are reasons to have high output currents, but 120A is unreasonable and 99.99% unlikely to be truly the real value of the amplifier output
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Old 8th January 2012, 09:52 AM   #5
marce is offline marce  United Kingdom
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Its more a marketing ploy than anything, it shows what the theoretical power output could be. Unless they lay their PCB's out for that sort of current though the tracks, connectors and wiring would have fun never mind a thin little voice coil.
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Old 8th January 2012, 09:56 AM   #6
johnrtd is offline johnrtd  Belgium
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Quote:
Originally Posted by back View Post
i see some class AB amps that state some huge current capability.
parasound 3500 120ampere peak.
musical fidelity supercharger 240 ampere peak.
there are more but you see my point.
what is the case if we compare that with 20-30 or even 50 amperes of
class d amps?

thanks in advance.
You have to read carefully! The mentioned currents are so-called peak values. These currents will only appear for some milliseconds (until the electrolytic capacitors in the power supply are discharged).
The currents for the class-D amps are specified as "continue" values!

John
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Old 8th January 2012, 10:06 AM   #7
back is offline back  Greece
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thanks for your replies guys.
a few more question.
how we calculate maximum output voltage at amps?
i know for class ab amps it`s the power supply voltage minus
a few losses but at how much distortion would that be?
is there a formula for that?
and for class d is the same?
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Old 8th January 2012, 10:13 AM   #8
back is offline back  Greece
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Quote:
Originally Posted by johnrtd View Post
You have to read carefully! The mentioned currents are so-called peak values. These currents will only appear for some milliseconds (until the electrolytic capacitors in the power supply are discharged).
The currents for the class-D amps are specified as "continue" values!

John
i know that but i don`t think so.
my amps datasheet says current limit 28A (stop mode after limiting for 80ms)

unless peak and continue is the same for class d but then what`s the point?
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Old 10th January 2012, 09:08 AM   #9
DjLeco is offline DjLeco  Romania
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Alot of marketing LIES, and stupid people believes.

To confirm that, take by example Powersoft amplifiers , wich have 15 Amperes fuses after rectification and storage capacitors.

How can it deliver 130 Amperes on output?

BIG lie, as the claimed 20000Watts from 12 Amperes breaker, at 120 volts, grace to thei WONDER PFC... Ha Ha ha.
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Old 10th January 2012, 02:14 PM   #10
back is offline back  Greece
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Quote:
Originally Posted by DjLeco View Post
Alot of marketing LIES, and stupid people believes.

To confirm that, take by example Powersoft amplifiers , wich have 15 Amperes fuses after rectification and storage capacitors.

How can it deliver 130 Amperes on output?

BIG lie, as the claimed 20000Watts from 12 Amperes breaker, at 120 volts, grace to thei WONDER PFC... Ha Ha ha.

so the class d manufacturers must be more honest
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