From: jl@glen--canyon.com   
      
   On Fri, 6 Mar 2026 19:43:58 -0000 (UTC), Phil Hobbs   
    wrote:   
      
   >ehsjr  wrote:   
   >> On 3/5/2026 11:09 PM, 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.   
   >>   
   >> The limiter I described addresses the OP's application, not yours:   
   >> "I feed in a small   
   >> signal, from my signal generator or from my analog computer, into my   
   >> LM386 amplifier (20x gain) and then to the speaker."   
   >>   
   >>   
   >>>   
   >>> Hint:  I haven't seen any commercial hi-fi amplifier schematics that   
   >>> include such diode clipper speaker protection.   
   >>   
   >> Nor I, but irrelevant to the OP.   
   >>   
   >> Ed   
   >>>   
   >>>   
   >>   
   >>   
   >   
   >Of course a series clipper would protect the speaker without shorting the   
   >amp. Needs a bit of auxiliary power, and would cause a bit of distortion,   
   >but nothing awful for a toy application.   
   >   
   >Personally I’d just crank down the LM386’s  supply voltage.   
   >   
   >Cheers   
   >   
   >Phil Hobbs   
      
   Of course an "8 ohm" speaker isn't really 8 ohms. Audio is such a   
   mess.   
      
   A tiny speaker will have basically no bass efficiency, so a series   
   (highpass) cap might protect it.   
      
   Imagine a true frequency-selective wattmeter, or a true-power spectrum   
   analyzer.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
   --- SoupGate-Win32 v1.05   
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