From: pcdhSpamMeSenseless@electrooptical.net   
      
   ehsjr  wrote:   
   > On 3/6/2026 9:56 AM, john larkin wrote:   
   >> On Thu, 05 Mar 2026 20:09:35 -0800, Jeff Liebermann    
   >> wrote:   
   >>   
   >>> On Thu, 5 Mar 2026 17:34:25 -0500, ehsjr  wrote:   
   >>>   
   >>>> On 3/5/2026 12:12 PM, Christopher Howard wrote:   
   >>>>>>   
   >>>>>> parallel protection1    parallel protection2   
   >>>>>> -+-[>>>>> |             |         |                         |   
   >>>>>> -+-[D3>]-[D4>]-+-       -+-[D5>]-[D6>]-[D7>]-[D8>]-+-   
   >>>>>>   
   >>>>>   
   >>>>> Thank you, would you mind please explaining a little more about these   
   >>>>> parallel protection circuits, i.e., how the protection works?   
   >>>>>   
   >>>>   
   >>>> Sure. The diodes act as simple voltage limiters.   
   >>>>   
   >>>> General purpose diodes conduct when the voltage across them rises   
   >>>> to about .7 volts. 2 diodes in series will conduct when the voltage   
   >>>> across the series pair is about 1.4 volts. Therefore a speaker with   
   >>>> a series pair of diodes across it won't be exposed to more than   
   >>>> roughly 1.4 volts, provided of course, that the diodes are installed   
   >>>> in the "right direction". Since a speaker usually is exposed to   
   >>>> an AC voltage, you need two diodes in one direction and two in   
   >>>> the other direction, so no matter what polarity signal is applied   
   >>>> to the speaker one or the other pair of diodes will limit the voltage.   
   >>>> 1A rated diodes can easily handle all the current a 386 is able   
   >>>> to provide.   
   >>>> Ed   
   >>>   
   >>> Two pairs of Si diodes will limit the audio (sine wave) to the speaker   
   >>> to 1.4 V peak to peak or 1.0 V RMS.  Into an 8 ohm loudspeaker, that's   
   >>> a fabulous:   
   >>> Power = E^2 / 8 = 0.13 watts RMS   
   >>> My home entertainment system claims it can deliver 50 watts[1], which   
   >>> will probably vaporize a simple diode voltage limiter.   
   >>>   
   >>> Hint:  I haven't seen any commercial hi-fi amplifier schematics that   
   >>> include such diode clipper speaker protection.   
   >>   
   >> A bridge rectifier has 4 diodes in one can.   
   >   
   > Trouble is, you can't use all 4 diodes in the bridge as a   
   > back to back diode bi-directional shunt limiter.   
   >   
   Sure you can. Wire the AC pins across the speaker and short the DC pins.   
      
   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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