XPost: sci.electronics.design   
   From: pcdhSpamMeSenseless@electrooptical.net   
      
   On 12/24/2017 04:46 PM, Steve Morris wrote:   
   > On 25/12/17 07:21, tabbypurr@gmail.com wrote:   
   >> On Sunday, 24 December 2017 19:47:00 UTC, Steve Morris  wrote:   
   >>> I was wondering what would happen if I wired the output of a 100W audio   
   >>> amplifier directly across a sizable (4700uF) electrolytic capacitor.   
   >>>   
   >>> It could be assumed the amp is push-pull and the cap is polarized.   
   >>>   
   >>> How would it react in terms of a test load?   
   >>>   
   >>> Steve Morris   
   >>   
   >> try sci.electronics.basics   
   >>   
   >   
   > Do you post there too?   
   >   
   > Steve Morris   
   >   
   >   
      
   Lots of us do.  No stigma attached, it's just not a design question.   
   (Cross-posted to s.e.basics)   
      
   The answer depends entirely on  whether the amp itself is stable with a   
   pathological load like that, and (assuming that it is) what its input is   
   and what the characteristics of the cap are.   
      
   If the amp output is just sitting at zero volts, it isn't going to do   
   anything dramatic to the cap.  If it oscillates, or if you put in a   
   large AC signal, and the cap is a smallish polarized electrolytic (as   
   opposed to a nonpolarized one), the cap probably isn't long for this   
   world, unless the amp dies or current-limits first.   
      
   The reactance of such a capacitor at (say) 10 kHz is   
      
   Xc = 1/( 2 pi * 10kHz * 4.7e-6 F) = 3.3 milliohms,   
      
   i.e. very nearly a short circuit.  The equivalent series resistance   
   (ESR) is probably more than that, so the cap looks like a very low   
   resistance.   
      
   The net is that depending on the characteristics of the amp and what you   
   put into it, your cap could be destroyed or could be completely unharmed.   
      
   Actual audio people will probably have a better handle on how your   
   average 100W amp will respond to such abuse.   
      
   Cheers   
      
   Phil Hobbs   
      
   --   
   Dr Philip C D Hobbs   
   Principal Consultant   
   ElectroOptical Innovations LLC / Hobbs ElectroOptics   
   Optics, Electro-optics, Photonics, Analog Electronics   
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   http://electrooptical.net   
   http://hobbs-eo.com   
      
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