[ARC5] Carbon cartridge replacement circuit

[kn7sfz]

That.....was.....exemplary!  Thanks Richard!

de kn7sfz


On 4/27/2017 6:28 PM, Richard Knoppow wrote:
>     A carbon microphone is an amplifier because the power out is 
> greater than the power in. The controlling force is the acoustic 
> energy available to the diaphragm, the diaphragm in turn converts the 
> acoustic energy to mechanical energy which moves one of the contacts 
> with the resistance element. This in turn varies the voltage across 
> the resistive element and varies the current applied to it. The input 
> energy, as absorbed from the air, is a small fraction of a watt but 
> the output can be very large depending on the dissipation of the 
> carbon element.  The action is rather like a vacuum tube which also 
> acts as a variable resistor. The input power to the grid is very small 
> compared to the output power from the plate the variation being in the 
> effective plate resistance.
>     One of the earliest attempts to make telephone repeaters, i.e. 
> amplifiers, was done by coupling a magnetic speaker or headphone to a 
> carbon microphone. These worked will enough to be used on experimental 
> long distance circuits but were ultimately not very satisfactory due 
> to excessive noise and distortion.
>     Other types of microphones are not amplifiers but either 
> generators or controllers.  Dynamic microphones, which includes moving 
> coil, magnetic, variable reluctance, balanced armature, and ribbon 
> types generate a voltage by moving a conductor through a magnetic 
> field or, in some cases, by moving the magnetic field. The energy 
> available to generate the output is only the amount that can be 
> absorbed from the sound wave. Piezo electric microphones depend on the 
> generating ability of crystals when deformed for their operation. 
> Again, the power available to deform the crystal is only as much as 
> can be absorbed from the sound wave.  Another type is the controller. 
> This includes the condenser and the related electret microphone. These 
> depend on the displacement of one plate of a capacitor. The output is 
> taken either by inposing a bias voltage across the plates and taking 
> the voltage difference as one plate moves with regard to the other. 
> The output is amplified by some sort of amplifier at the microphone. 
> Another type uses the variable capacitor to change the frequency of an 
> RF oscillator the FM output being detected and put out as an audio 
> signal. Since neither form generates a voltage directly they are 
> neither generators or amplifiers although they are used with some form 
> of amplifier.  An electret is the same as a condenser mic but uses a 
> dielectric which holds a permanent charge. Again, the mic must be 
> associated with a very high impedance amplifier that does not absorb 
> power from the electrodes.
>    In a way the carbon microphone and condenser microphone are similar 
> because both depend on an external source of power to operate but 
> while the condenser or electret requires an electronic amplifier to 
> work the carbon microphone stands alone as both the sound sensor and 
> an amplifier.