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K3DSPLPF Low Pass Filter

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Dick Dickinson

K3DSPLPF Low Pass Filter

I'm a SSB operator and am interested in the Low Pass Filter Update/Mod.

Can someone with a pre-Rev D DSP board who has installed the K3DSPLPF speak
to the improvements?

Thanks.

73,
Dick - KA5KKT

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Brett Howard

Re: K3DSPLPF Low Pass Filter

Makes the radio sound a lot quieter and less fatiguing to me.

Honestly I feel much more comfortable for long periods of time behind
the K3 after installing the filter. I should state that I changed the
filter and several of the output caps at the same time.

I even tried to do some filters in the computer to simulate what I
should expect and I didn't really hear the difference so much in those
files but once the filter was in the radio I noticed a difference.

I have pictures of the differences that you can see here:
<a href="http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/Wide%20Band%">http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/Wide%20Band%
20noise%20injected%202.8Khz%20BW.png
<a href="http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/1uV%20850Hz%">http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/1uV%20850Hz%
20BW.png
<a href="http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/50uV%20Signal%">http://dl.dropbox.com/u/1493706/K3/Audio%20Filter%20Board/50uV%20Signal%
20850Hz%20BW.png

In all 3 pictures the green trace is before the LPF board was installed
and the red trace is after. I should also note that the sample rate was
different between the two captures and that is the reason behind the
difference at the very high end...

Anyway those are my thoughts... Some subjective and some not so
subjective... Hopefully that helps.

~Brett

On Mon, 2010-03-01 at 11:40 -0500, Edward Dickinson, III wrote:

> I'm a SSB operator and am interested in the Low Pass Filter Update/Mod.
>
> Can someone with a pre-Rev D DSP board who has installed the K3DSPLPF speak
> to the improvements?
>
> Thanks.
>
>
> 73,
> Dick - KA5KKT
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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Joe Planisky

Re: K3DSPLPF Low Pass Filter

In reply to this post by Dick Dickinson

I recently installed the LPF. I did *not* make any other changes
(e.g. to extend the low frequency response.) I work mostly CW but do
a fair amount of listening to SSB and SWBC.

In my case, the effect is rather subtle and I can't be sure it's not
just a placebo effect, but I think CW notes and SSB voices sound a bit
smoother. I haven't used it for a long period of time since I
installed the LPF, so I can't really tell if it's less fatiguing.

Like Brett, I have before and after spectrum plots which clearly show
that the aliased passband images centered on 12 kHz are completely
gone. However, in my case the 12 kHz clock leakage itself is still
there. It must be getting into the output some other way than through
the normal audio path.

It was one of the more challenging mods that I've done to my K3,
mostly due to the fact that 4 of the 6 vias used were filled with
solder, two of which have an IC on the other side preventing the use
of a hot needle to clear them. And I'm *always* nervous cutting
traces. That said, it wasn't really difficult. I took my time and
spent about 2 hours from power off to power on.

I noticed the price on the LPF board has gone up to $35. When I
ordered mine it was $25. Was it worth it? I think so. I wouldn't
call it a whole-new-rig difference but I seem to think the rig is a
bit more pleasant to listen to.

73
--
Joe KB8AP

On Mar 1, 2010, at 8:40 AM, Edward Dickinson, III wrote:

> I'm a SSB operator and am interested in the Low Pass Filter Update/
> Mod.
>
> Can someone with a pre-Rev D DSP board who has installed the
> K3DSPLPF speak
> to the improvements?
>
> Thanks.
>
>
> 73,
> Dick - KA5KKT
>

Bob Cunnings NW8L

Re: K3DSPLPF Low Pass Filter

I also installed the LPF in 2 K3s here this weekend. Although I have
pretty good hearing, I was skeptical about any possible improvement.
However, I was surprised when I turned on the 1st unit completed. The
improvement was noticeable (I use headphones with a wide frequency
response). CW notes are purer, and atmospheric noise less grating. AF
output from the headphone jack looks very clean now when viewed on
Spectrum Lab, previously the artifacts were no better than 60 dB down
with strong signals. There is no change to the line out audio, which
uses a separate DAC and audio path.

All vias were solder filled on both units, but I was able to clear
them with solder wick and the installation went smoothly. The
instructions are very clear. I also did not make the change to extend
low frequency response.

Bob NW8L

On Mon, Mar 1, 2010 at 11:02 PM, Joe Planisky <[hidden email]> wrote:

> I recently installed the LPF. I did *not* make any other changes
> (e.g. to extend the low frequency response.) I work mostly CW but do
> a fair amount of listening to SSB and SWBC.
>
> In my case, the effect is rather subtle and I can't be sure it's not
> just a placebo effect, but I think CW notes and SSB voices sound a bit
> smoother. I haven't used it for a long period of time since I
> installed the LPF, so I can't really tell if it's less fatiguing.
>
> Like Brett, I have before and after spectrum plots which clearly show
> that the aliased passband images centered on 12 kHz are completely
> gone. However, in my case the 12 kHz clock leakage itself is still
> there. It must be getting into the output some other way than through
> the normal audio path.
>
> It was one of the more challenging mods that I've done to my K3,
> mostly due to the fact that 4 of the 6 vias used were filled with
> solder, two of which have an IC on the other side preventing the use
> of a hot needle to clear them. And I'm *always* nervous cutting
> traces. That said, it wasn't really difficult. I took my time and
> spent about 2 hours from power off to power on.
>
> I noticed the price on the LPF board has gone up to $35. When I
> ordered mine it was $25. Was it worth it? I think so. I wouldn't
> call it a whole-new-rig difference but I seem to think the rig is a
> bit more pleasant to listen to.
>
> 73
> --
> Joe KB8AP
>