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27th March 2012, 07:44 AM  #2211  
diyAudio Member

Quote:
really do not understand ur logic here. I thought that it was well understood, in the final analysis, that BJT's are in fact voltage controlled with finite resistance whereas FETs are voltage controlled with almost infinite resistance. You seem to be attempting to wrap up your preference for BJTs in some kind of logic  but all I'm hearing is that you have a preference for BJTs. 

27th March 2012, 07:52 AM  #2212  
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Join Date: Dec 2007

Quote:


27th March 2012, 07:59 AM  #2213 
diyAudio Member

Oh ok then, must be the text book I read was wrong.

27th March 2012, 08:26 AM  #2214 
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Join Date: Dec 2007


27th March 2012, 08:58 AM  #2215  
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Join Date: Dec 2007

Quote:
The CCS forces a current which is a linear multiple of control current. No need for Vas. 

27th March 2012, 04:37 PM  #2216 
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Join Date: Sep 2007

Hi hahfran
That's completely wrong approach. All power amplifiers have to follow voltage gain linearly according to frequency. Why? Because all the speakers's sound pressure is linearized to input voltage at their terminals. Impedance curve is much more unlinear and has no correlation to sound pressure curve even at driver's resonance frequency. Current amplifier would make a speaker sound completely wrong because SPL would follow impedance curve and that would be a real mess. We have to make amplifier's gain linear to input voltage and to have output impedance as low as possible (high damping factor). Power supply and numerous BJT output pairs enables high current capability. Basics of audio ... 
27th March 2012, 05:22 PM  #2217  
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Join Date: Dec 2007

Quote:
that is the mechanical motion equation. All one has to do is to feed a current amp with the output of an "analog computer" ( 3 integrators and one adder ) to cancel out all of the mechanical constants such as mass compliance...and electrical constants such as resistance and inductivity of the voice coil. So far only swedish co ACE employs this approach. It gets a bit simpler with positive feedback from a resistors in series with the speaker. of course the real speaker does not follow a simple second order de but it is a simple and easy to implement approach. 

27th March 2012, 05:28 PM  #2218 
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Join Date: Dec 2007

I am not telling anything new here. Of course one has to map the mechanical stuff onto an electrical schematic and the whole trick is to give the amp a complex output impedance which is exactly the reverse ( the mirror image in complex plane) of the speaker's electrical equivalent. It took a very long time until makers of active speakers adopted this most simple idea but now all of them do it.

27th March 2012, 06:02 PM  #2219 
diyAudio Member
Join Date: Dec 2007

Back to the roots
provided the model provided by Bob Cordell is correct and the schematic is correct I get an op of 1.8 amps drain current . Is that correct? 
27th March 2012, 10:36 PM  #2220 
diyAudio Member
Join Date: Jan 2010

Hi LC !
How much slew rate does this version has? Thanks again for this wonderful design ! 
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