class D vs class AB current capability.
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 Class D Switching Power Amplifiers and Power D/A conversion

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 8th January 2012, 07:58 AM #1 back   diyAudio Member   Join Date: Nov 2005 Location: crete 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.
 8th January 2012, 09:05 AM #2 trevmar   diyAudio Member   Join Date: Jan 2011 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
back
diyAudio Member

Join Date: Nov 2005
Location: crete
Quote:
 Originally Posted by trevmar 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.

 8th January 2012, 09:50 AM #4 trevmar   diyAudio Member   Join Date: Jan 2011 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
 8th January 2012, 09:52 AM #5 marce   diyAudio Member   Join Date: Jun 2007 Location: Blackburn, Lancs 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.
johnrtd
diyAudio Member

Join Date: Oct 2003
Location: Ledegem Belgium
Quote:
 Originally Posted by back 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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 8th January 2012, 10:06 AM #7 back   diyAudio Member   Join Date: Nov 2005 Location: crete 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?
back
diyAudio Member

Join Date: Nov 2005
Location: crete
Quote:
 Originally Posted by johnrtd 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?

 10th January 2012, 09:08 AM #9 DjLeco   diyAudio Member   Join Date: Oct 2006 Location: Bucharest, Romania 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.
back
diyAudio Member

Join Date: Nov 2005
Location: crete
Quote:
 Originally Posted by DjLeco 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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