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21st December 2012, 09:13 AM  #21 
diyAudio Member
Join Date: May 2008

I do not understand your post exactly though i suppose you speak about the Vbe multiplier.
If so, for more current into the output stage: increase Rb2 Refering to:Page 12 of LME49811 datasheet VBIAS= VBE(1+Rb2/Rb1) Last edited by bobodioulasso; 21st December 2012 at 09:26 AM. 
21st December 2012, 11:55 AM  #22 
diyAudio Member
Join Date: Oct 2009
Location: Brisbane, Australia

I really think you need to spend more time reading datasheets. the LME chips have a VERY well documented amplifier application note that answers all (or at least many) of your questions.

24th December 2012, 07:42 PM  #23  
diyAudio Member
Join Date: Aug 2012

Quote:
so in the above case it can give about 2Amps of output if increasing the Rb2 so what is the maximum bias current that I can achieve with this? what are the limitations? like I want to bias till 2.5 amps can I do that? what is the max limit on what factor it is dependent? 

24th December 2012, 08:00 PM  #24  
diyAudio Member
Join Date: Aug 2012

Quote:
so using 4 pairs of output devices is enough for safe operation? and no thermal runaway? but I still have a question that do we need an external driver to feed the base current or Gate current to the output stages? since according to you each pair requires about 2.5 amps so for all 8 devices its 20 amps of continuous current! the big question is that how considering that this amp would deliver 100W of class A power then what should be the psu rating? 2KVa? preferably safe... but can you tell me what driver to use to give 2.5 amps for each output device? 

24th December 2012, 08:22 PM  #25 
diyAudio Member
Join Date: Aug 2012

but technically class A amplifier pow is calculated as I x I x R example in your case 2.5 bias current which is continuous and peak its considered as 5 amps and for 5 x 5 x 8 ohms 200W peak and in RMS its 141W RMS
but my prob is what should be the gate current for each output device example toshiba 2sj201 output mosfet? what driver to use and how many stages to be used for the above power? 
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