Elecraft

K3 Audio Low Pass Filter

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pd0psb

K3 Audio Low Pass Filter

Hi all,

There were some complaints about spurious DSP/DAC products *above* the K3
passband response.
The mentioned (beta) LPF board is only meant to supress those products.
It does not alter the K3 passband AF response or character.
If you don't hear any spurious above passband this LPF is not going to make
any difference for you.

It is working on both headphones and speaker outputs.

73'
Paul
PD0PSB
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Mike Scott-7

Re: K3 Audio Low Pass Filter

>G'day,
>What about - how did it perform?
>...does it in any way respond to the "pink" vs. "white" noise thread of a
few weeks ago.
>Mike VP8NO

Mike,
I am still evaluating but I believe the LP filter took the harshness out of
my audio. I had been one of people with a complaint about harsh audio and so
far I like it. I seem to have distortion products above the intended audio
passband that this filter cuts out. That extra stuff made it fatiguing for
me; other people don't hear it. I understand that some people can be
fatigued by odd order harmonic distortion even when the distortion is way
down.

I am not set up to compare with another radio and I can't do an A-B test as
the filter is hardwired in. I plan to live with this set up for a while and
maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
will replace with 100 uF SMD devices like the current production caps.

The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
around to putting a pink noise filter into the DSP.

I am experimenting with the following Rx EQ settings from another post to
simulate a pink noise filter:
1 +0
2 +8
3 +2
4 -1
5 -1
6 -3
7 -5
8 -10

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1 #1311

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Brett Howard

Re: K3 Audio Low Pass Filter

I did an A/B test with before and after measurements at the speaker out
port. The difference in the VERY high frequency where that drop off
occurs is because of a sample rate difference and should make no
difference in the lower frequency information. The wide band plot makes
it pretty obvious what the filter is designed to take out around 11 to
13 Khz or so...

Anyway hope this clears things up a bit as to what its designed to do.
it gives a much beloved openness and clarity to the sound. I had no
problems spending a good long time behind the radio at FD. I think I
was behind that thing from 11 to 3AM with only very short breaks.

~Brett

On Sat, 2009-07-04 at 10:20 -0700, Mike Scott wrote:

> >G'day,
> >What about - how did it perform?
> >...does it in any way respond to the "pink" vs. "white" noise thread of a
> few weeks ago.
> >Mike VP8NO
>
> Mike,
> I am still evaluating but I believe the LP filter took the harshness out of
> my audio. I had been one of people with a complaint about harsh audio and so
> far I like it. I seem to have distortion products above the intended audio
> passband that this filter cuts out. That extra stuff made it fatiguing for
> me; other people don't hear it. I understand that some people can be
> fatigued by odd order harmonic distortion even when the distortion is way
> down.
>
> I am not set up to compare with another radio and I can't do an A-B test as
> the filter is hardwired in. I plan to live with this set up for a while and
> maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
> will replace with 100 uF SMD devices like the current production caps.
>
> The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
> somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
> KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
> around to putting a pink noise filter into the DSP.
>
> I am experimenting with the following Rx EQ settings from another post to
> simulate a pink noise filter:
> 1 +0
> 2 +8
> 3 +2
> 4 -1
> 5 -1
> 6 -3
> 7 -5
> 8 -10
>
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1 #1311
>
>
>
>
>
> ______________________________________________________________
> 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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Gregg W6IZT

Re: K3 Audio Low Pass Filter

In reply to this post by Mike Scott-7

What are the values of the components for filter?

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Mike Scott
Sent: Saturday, July 04, 2009 1:21 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 Audio Low Pass Filter

>G'day,
>What about - how did it perform?
>...does it in any way respond to the "pink" vs. "white" noise thread of a
few weeks ago.
>Mike VP8NO

Mike,
I am still evaluating but I believe the LP filter took the harshness out of
my audio. I had been one of people with a complaint about harsh audio and so
far I like it. I seem to have distortion products above the intended audio
passband that this filter cuts out. That extra stuff made it fatiguing for
me; other people don't hear it. I understand that some people can be
fatigued by odd order harmonic distortion even when the distortion is way
down.

I am not set up to compare with another radio and I can't do an A-B test as
the filter is hardwired in. I plan to live with this set up for a while and
maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
will replace with 100 uF SMD devices like the current production caps.

The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
around to putting a pink noise filter into the DSP.

I am experimenting with the following Rx EQ settings from another post to
simulate a pink noise filter:
1 +0
2 +8
3 +2
4 -1
5 -1
6 -3
7 -5
8 -10

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1 #1311

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Brett Howard

Re: K3 Audio Low Pass Filter

Not sure as I don't have a schematic... Somewhere I wrote down the amp
that was used.... I'm sure that we could ask for it I just hadn't
gotten around to it. It is an active filter though...

~Brett

On Sat, 2009-07-04 at 17:35 -0400, Gregg W6IZT wrote:

> What are the values of the components for filter?
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Mike Scott
> Sent: Saturday, July 04, 2009 1:21 PM
> To: [hidden email]
> Subject: Re: [Elecraft] K3 Audio Low Pass Filter
>
> >G'day,
> >What about - how did it perform?
> >...does it in any way respond to the "pink" vs. "white" noise thread of a
> few weeks ago.
> >Mike VP8NO
>
> Mike,
> I am still evaluating but I believe the LP filter took the harshness out of
> my audio. I had been one of people with a complaint about harsh audio and so
> far I like it. I seem to have distortion products above the intended audio
> passband that this filter cuts out. That extra stuff made it fatiguing for
> me; other people don't hear it. I understand that some people can be
> fatigued by odd order harmonic distortion even when the distortion is way
> down.
>
> I am not set up to compare with another radio and I can't do an A-B test as
> the filter is hardwired in. I plan to live with this set up for a while and
> maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
> will replace with 100 uF SMD devices like the current production caps.
>
> The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
> somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
> KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
> around to putting a pink noise filter into the DSP.
>
> I am experimenting with the following Rx EQ settings from another post to
> simulate a pink noise filter:
> 1 +0
> 2 +8
> 3 +2
> 4 -1
> 5 -1
> 6 -3
> 7 -5
> 8 -10
>
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1 #1311
>
>
>
>
>
> ______________________________________________________________
> 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
>
> ______________________________________________________________
> 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

Brett Howard

Quick Question for someone with their radio open

In reply to this post by Gregg W6IZT

http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsCnlYck6hSqNv1tvAH8HUqxGXBxSgy5Fs%3d

I think this capacitor may fit into the C9 and C13 area next to the
headphone. This is an only 10V cap rather than the 25V cap that
Elecraft has in there now. But I think that should be plenty of
derating for a 105mW power amp.

So if anyone has a pair of calipers and their radio open I'd be
interested to see if we think this thing will fit.

The bottom pad in the direction other than that with leads is ~5.3mm
or .208" and in the direction of the leads its going to be ~5.5mm
or .217 inches to the outside of the leads.

Would greatly appreciate if someone would confirm this for me. I
remember taking these measurements but didn't write them down. I
believe I'm remembering them correctly.

Anyone else have any thoughts on if 10V is going to be enough? I
figured 10V^2/16ohms is about 6.25 watts and being that the amp is
designed to deliver 105mW to that 16ohm load that seems like it should
be more than enough derating. Any other thoughts?

~Brett

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Brett Howard

Re: Quick Question for someone with their radio open

Take that back... Looks like Mouser's website was lying that that was a
5mm diameter cap.... Its actually 6.3mm which is going to be too big...

So I did a bit more digging and found:
http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsCnlYck6hSqLKeSeHnSOGyVYzpVBYnbJA%3d

Looks like this specific cap should fit the pads. Providing the .208"
measurement that I think I remember correctly isn't way off in left
field... :)

If someone could verify the dimensions of the plastic nugget on the
bottom is about .208" x .208" then I think I'll have to order me up a
few of these.

~Brett

On Sat, 2009-07-04 at 20:51 -0700, Brett Howard wrote:

> http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsCnlYck6hSqNv1tvAH8HUqxGXBxSgy5Fs%3d
>
> I think this capacitor may fit into the C9 and C13 area next to the
> headphone. This is an only 10V cap rather than the 25V cap that
> Elecraft has in there now. But I think that should be plenty of
> derating for a 105mW power amp.
>
> So if anyone has a pair of calipers and their radio open I'd be
> interested to see if we think this thing will fit.
>
> The bottom pad in the direction other than that with leads is ~5.3mm
> or .208" and in the direction of the leads its going to be ~5.5mm
> or .217 inches to the outside of the leads.
>
> Would greatly appreciate if someone would confirm this for me. I
> remember taking these measurements but didn't write them down. I
> believe I'm remembering them correctly.
>
> Anyone else have any thoughts on if 10V is going to be enough? I
> figured 10V^2/16ohms is about 6.25 watts and being that the amp is
> designed to deliver 105mW to that 16ohm load that seems like it should
> be more than enough derating. Any other thoughts?
>
> ~Brett
>

n7ws

Re: K3 Audio Low Pass Filter

In reply to this post by pd0psb

--- On Sat, 7/4/09, Mike Scott <[hidden email]> wrote:

Mike,
I am still evaluating but I believe the LP filter took the harshness out of
my audio. I had been one of people with a complaint about harsh audio and so
far I like it. I seem to have distortion products above the intended audio
passband that this filter cuts out. That extra stuff made it fatiguing for
me; other people don't hear it. I understand that some people can be
fatigued by odd order harmonic distortion even when the distortion is way
down.

Absolutely. There is simply no excuse for the levels of audio distortion that exists in some modern receivers. IMHO, distortion not only adds to fatigue, but negatively affects intelligibility, particularly on weak signals buried in noise, such as those on EME.

It seems to me that since audio is the desired output, the design process should be to design an excellent audio system first and then work back toward the antenna. Regrettably, it seems this is the converse of how it works and the audio system becomes an afterthought, with some designers believing that <10% THD is "good enough" for "communications" audio.

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Geoffrey Mackenzie-Kennedy

Re: [SPAM] Re: K3 Audio Low Pass Filter

On Sunday, July 05, 2009 at 3:54 PM, Wes Stewart<[hidden email]> wrote:

> It seems to me that since audio is the desired output, the design process
> should be to design an excellent audio system first and then work back
> toward the antenna. Regrettably, it seems this is the >
> converse of how it works and the audio system becomes an afterthought,
> with some designers believing that <10% THD is "good enough" for
> "communications" audio.

Another good reason for running odd order dynamic range tests with both
applied signals inside the overall passband when reviewing a receiver, may I
suggest.

73,
Geoff
GM4ESD

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Dick Dickinson

Re: K3 Audio Low Pass Filter

In reply to this post by pd0psb

"Communications" audio can be like being mugged and beaten...just as long as
you get the message.

Best regards,
Dick - KA5KKT

...believing that <10% THD is "good enough" for "communications" audio.

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