[Elecraft] K3 Audio Low Pass Filter

[Joe Subich, W4TV]

> Its installed in the speaker outputs.

That's a shame,  It should be in the common feed to both 
the headphone and speaker amplifiers. 

> I should take a look and see if the headphone 
> output had that 11-12khz stuff on it... 

Yes, it's coming out of the DSP DAC ... it's present on all 
three (headphone, speaker and line) outputs. 

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Brett Howard
> Sent: Friday, July 03, 2009 9:08 PM
> To: Bob Cunnings
> Cc: Elecraft
> Subject: Re: [Elecraft] K3 Audio Low Pass Filter
> 
> 
> Its installed in the speaker outputs.  So it doesn't modify 
> the headphone circuits but I use it via speaker at home most 
> of the time... I should take a look and see if the headphone 
> output had that 11-12khz stuff on it...
> 
> ~Brett
> 
> On Fri, 2009-07-03 at 18:21 -0600, Bob Cunnings wrote:
> > What is the point of insertion (in terms of the schematic) for this 
> > filter?
> > 
> > Bob NW8L
> > 
> > On Fri, Jul 3, 2009 at 6:09 PM, Brett 
> Howard<brett at livecomputers.com> 
> > wrote:
> > > Its a low pass filter starting around 3.8Khz or so.  I have some 
> > > before and after plots.  I just need to get around to 
> posting them 
> > > so I can put them up on the reflector.
> > >
> > > On Fri, 2009-07-03 at 19:45 -0400, Mike Harris wrote:
> > >> G'day,
> > >>
> > >> | All in all I'm quite pleased with the sound difference.
> > >> |
> > >> | ~Brett
> > >>
> > >> OK, that's couple of positive comments.  Is there any technical 
> > >> data on the characteristics of this filter.  For 
> example, does it 
> > >> in any way respond to the "pink" vs. "white" noise 
> thread of a few 
> > >> weeks ago.
> > >>
> > >> I've become rather more interested in this since 
> reactivating my K2 
> > >> and running it side by side with the K3.  The K2 sounds so much 
> > >> nicer even in the presence of a received S3 buzzy 
> background noise.  
> > >> If only the K2 power overshoot on 40M SSB didn't give my 
> amp a hard 
> > >> time...
> > >>
> > >> Now to put this in context, there was a huge improvement 
> in the K2 
> > >> as soon as I installed the analogue af CW filter years 
> ago.  In SSB 
> > >> mode the filter just introduces a low pass filter which 
> takes the 
> > >> hiss out of the audio and made it really smooth to listen to.
> > >>
> > >> I have played with the DSP bandwidth settings and 
> replicated the K2 
> > >> af spectrum as displayed in Spectrogram to see if I can 
> make them 
> > >> sound the same but they don't.
> > >>
> > >> My agc and equalizer settings are nothing unusual or extreme.
> > >>
> > >> Regards,
> > >>
> > >> Mike VP8NO
> > >> K2 #1400
> > >> K3 #345