From: ehsjr@verizon.net   
      
   On 3/6/2026 2:46 PM, Phil Hobbs wrote:   
   > 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   
   >   
   >   
   >   
      
   Doh. Of course.   
   Thanks!   
   Ed   
      
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