[Elecraft] K3 Audio Low Pass Filter

[Paul Christensen]

> The 8.2 ohms is actually in the K3.  If I do it again for your 32 ohm
> example I get 39Hz.  With your 220uF cap that moves it down to ~18Hz for a
> pair of 32ohm cans.

And that jumps to ~ 200 Hz if you use 8-ohm cans.  If you stay cognizant of 
the headphone Z, you're in good shape.  If you want to pull a set of Koss 
Pro4 AA phones off the shelf, you may want to revisit that.  It's all about 
the series C and knowing the headphone Z as a function of frequency.  It's 
doubtful your 27 ohms headphones remain 27 ohms across their frequency 
range.

> Personally I think the more robust connection is a good point to keep and
> I'm ok with the 45Hz output.  I tried running things through my headphone

Speaking of robust, when I started discussing the matter with Lyle many 
months ago, I was concerned that increasing the C value above 10 uF at 
C9/C13 would begin to introduce switching thumps that would become apparent 
especially in CW.  Stated another way, I was hopeful that the small C size 
was not masking keying artifacts that were there all along, only to be 
discovered by increasing the cap size!  But at 330 uF, I hear no artifacts 
as a result of the change.

Pul, W9AC