[Elecraft] K3 Audio Low Pass Filter

[Alan Bloom]

On Mon, 2009-07-06 at 11:23 -0400, Paul Christensen wrote:
> > I've been informed Elecraft is already replacing those caps with 100uF
> > caps in the current production units.
...
> Why would anyone want a higher value than 100 uF at C9/C13?  Consider a set 
> of modern, medium-Z headphones with a Z of 32 ohms at 100 Hz.  The -3dB 
> turnover point calculates to roughly 150 Hz.  

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.

If you want better low-frequency response, just stick a resistor in
series with the speaker.  That does mean you have to turn up the volume,
but you do get plenty of bass (assuming your speaker or phones can go
that low).  A 33-ohm resistor would give as much bass as your headphones
are likely to be able to reproduce.

Al N1AL