Class A Bias
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 30th December 2013, 09:23 PM #1 diyAudio Member     Join Date: Apr 2006 Location: italia - ora USA -WI Class A Bias Hi everybody, If with a bridge topology at +4A per rail per side at +/- 42V DC Rail is given, the total power dissipation is about 672W. Let's say it is roughly a little over 400W peak Class A power. Given a 220mF capacitor bank on each rail, how can I correlate the idle power dissipation at the primary with the power dissipation of the secondary, keeping in consideration that the charging current for the reservoir bank brings brings peak current of 46A at the secondary after rectifier thus peak current of over +/- 22A at the primary (this will significantly increase the RMS current thus power consumption) ? That would suggest that an amp with less capacitance will idle less power for a same given amount of Class A bias(?!?) Is this statement true? __________________ Stefano
 30th December 2013, 09:54 PM #2 diyAudio Member   Join Date: Nov 2003 Location: Brighton UK Hi, I'm pretty sure its not true in any significant sense, rgds, sreten. I can't follow the argument to arrive at the suggested conclusion. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
 30th December 2013, 10:15 PM #3 diyAudio Member   Join Date: Feb 2009 i cant see it.
 30th December 2013, 10:23 PM #4 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain surprised ? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb ; Papatreasure
diyAudio Member

Join Date: Apr 2006
Location: italia - ora USA -WI
Quote:
 Originally Posted by sreten Hi, I'm pretty sure its not true in any significant sense, rgds, sreten. I can't follow the argument to arrive at the suggested conclusion.
The argument is that if for a given amount of bias you have more capacitance, your peak current to charge this capacitance will be much higher than if you had less capacitance, which will reflect in an higher RMS current at the primary which ultimately translates into a huge amount if idle power.

The XA200.5 consumes roughly 700W idle but yet has 100mF per rail and 3.6A bias, which seems to be a pretty low figure compare to what I measure on my amp.
Maybe going from 100mF to 200mF causes the consumption to go from 700W to 1.2KW.
But then looking at the specs for the XS300 series which boosts twice as much capacitance as the XA, power consumption is still roughly 3 times the power rated power.
__________________
Stefano

diyAudio Member

Join Date: Apr 2006
Location: italia - ora USA -WI
Quote:
 Originally Posted by Zen Mod surprised ?
Yes and no. I just don't understand how the XA200.5 can idle only 700W
__________________
Stefano

 30th December 2013, 10:39 PM #7 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain I'm not surprised __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb ; Papatreasure
diyAudio Member

Join Date: Apr 2006
Location: italia - ora USA -WI
Quote:
 Originally Posted by Zen Mod I'm not surprised
Ok then would you mind explain why the 200.5 seems to idle less than what I would expect fo and get from the same bias setting?
__________________
Stefano

 30th December 2013, 11:00 PM #9 diyAudio Member   Join Date: Feb 2009 here is a Peace of ohms Law. its called voltage
 30th December 2013, 11:02 PM #10 diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain nope I already was idiot few times , trying to help you now , I like more to be idiot for my own causes __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; Mighty ZM's Bloggg;I'm dumb ; Papatreasure

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