[Elecraft] K3 Audio Low Pass Filter

[Paul Christensen]

> Actually, 100 uF into 32 ohms gives 50 Hz bandwidth at -3 dB.  Into an
> 8-ohm load you get 200 Hz at -3 dB, still fine for a voice signal
> although marginal for music.

Right, nearly 200 Hz on the money.  I think you're trivializing the 
difference between 200 Hz and 100 Hz with voice, not just music.  If a 
transmitter is capable of transmitting down to 100 Hz, the ear can hear 
substantial difference between those two extremes.  Arguably, we can say 
that all we really need is 300 Hz or even a bit higher for maximum 
articulation.  But, I'm discussing headphone circuit improvements primarily 
for AM as well as ESSB.

> If you want better low-frequency response, just stick a resistor in
> series with the speaker.

No doubt, as long as the output is not already volume-starved.  Also, 
another benefit of a low-Z source is the higher damping factor involved into 
low Z.  Adding pure series R to the output kills that attribute.

Paul, W9AC