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K3 Audio Low Pass Filter

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Mike Scott-7

K3 Audio Low Pass Filter

I just completed an installation of the K3 audio low pass filter board, the
one Lyle put out to individuals who wanted to try it. I was busy until now
as the boards came out some time ago.

It took a lot longer than expected because all the K3 DSP board holes were
full of solder. The instructions seemed to indicate that four of the holes
should have been clear, i.e., just stick the leads through. The instructions
seemed to be missing a section though as they never suggested soldering four
of the wires. I thought maybe a page was missing but the step numbers didn't
seem to indicate missing steps. Anyway, solder wick and solder suckers
didn't work. The holes are very small and it is tight quarters where a
miscue of the soldering iron could cause damage. I finally had to heat the
wire I wanted to put in the holes (resistor leads) and heat my way through
the soldered holes.

For future reference, what would be the right way to do this?

I would like to consider making more audio modifications, the one changing
headphone audio coupling capacitors to larger values for example. I looked
at those capacitors and I wondered how I was going to get them out. The
solder leads on one side seemed to be down at the bottom of a narrow canyon
caused by interfering components.

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

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AC7AC

Re: K3 Audio Low Pass Filter

CONTENTS DELETED

The author has deleted this message.

Mike Harris-9

Re: K3 Audio Low Pass Filter

In reply to this post by Mike Scott-7

G'day,

What about - how did it perform?

Regards,

Mike VP8NO

----- Original Message -----
From: "Mike Scott" <[hidden email]>
To: <[hidden email]>
Sent: Friday, July 03, 2009 4:04 PM
Subject: [Elecraft] K3 Audio Low Pass Filter

|I just completed an installation of the K3 audio low pass filter board,
the
| one Lyle put out to individuals who wanted to try it. I was busy until
now
| as the boards came out some time ago.
|
| It took a lot longer than expected because all the K3 DSP board holes
were
| full of solder. The instructions seemed to indicate that four of the
holes
| should have been clear, i.e., just stick the leads through. The
instructions
| seemed to be missing a section though as they never suggested soldering
four
| of the wires. I thought maybe a page was missing but the step numbers
didn't
| seem to indicate missing steps. Anyway, solder wick and solder suckers
| didn't work. The holes are very small and it is tight quarters where a
| miscue of the soldering iron could cause damage. I finally had to heat
the
| wire I wanted to put in the holes (resistor leads) and heat my way
through
| the soldered holes.
|
| For future reference, what would be the right way to do this?
|
| I would like to consider making more audio modifications, the one
changing
| headphone audio coupling capacitors to larger values for example. I
looked
| at those capacitors and I wondered how I was going to get them out. The
| solder leads on one side seemed to be down at the bottom of a narrow
canyon
| caused by interfering components.
|
| 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

In reply to this post by AC7AC

When I installed mine I just filled up the Via's a bit more and then was
able to get it all easily with the solder sucker. Although I was using
a sucker connected to house air and capable of RoHS temps (although I'm
not sure if I stepped up into those ranges).

The board went in quite smoothly and I was very pleased with the sound
enhancements.

As far as installation I did a lil trick in that I put in the wires (all
6 of them) then cut each wire at a different height. That allows you to
align each wire one at a time. Then I used the knurled nut from the
headphones jack as a spacer off of the main DSP board before
soldering.

All in all I'm quite pleased with the sound difference.

~Brett

On Fri, 2009-07-03 at 13:39 -0700, Ron D'Eau Claire wrote:

> I don't know who wrote the instructions you got. I've not worked on
> installing that board.
>
> It sounds like it uses some open vias (the round 'grommets' that join traces
> different opposite layers of the board together.
>
> I'd bet the person who created the document had a version with open vias.
> However, I've noticed that some boards have the vias open and others have
> them full of solder.
>
> Ron AC7AC
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Mike Scott
> Sent: Friday, July 03, 2009 1:05 PM
> To: [hidden email]
> Subject: [Elecraft] K3 Audio Low Pass Filter
>
> I just completed an installation of the K3 audio low pass filter board, the
> one Lyle put out to individuals who wanted to try it. I was busy until now
> as the boards came out some time ago.
>
> It took a lot longer than expected because all the K3 DSP board holes were
> full of solder. The instructions seemed to indicate that four of the holes
> should have been clear, i.e., just stick the leads through. The instructions
> seemed to be missing a section though as they never suggested soldering four
> of the wires. I thought maybe a page was missing but the step numbers didn't
> seem to indicate missing steps. Anyway, solder wick and solder suckers
> didn't work. The holes are very small and it is tight quarters where a
> miscue of the soldering iron could cause damage. I finally had to heat the
> wire I wanted to put in the holes (resistor leads) and heat my way through
> the soldered holes.
>
> For future reference, what would be the right way to do this?
>
> I would like to consider making more audio modifications, the one changing
> headphone audio coupling capacitors to larger values for example. I looked
> at those capacitors and I wondered how I was going to get them out. The
> solder leads on one side seemed to be down at the bottom of a narrow canyon
> caused by interfering components.
>
> 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]
>
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> 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

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P.B. Christensen

Re: K3 Audio Low Pass Filter

> I would like to consider making more audio modifications, the one changing
> headphone audio coupling capacitors to larger values for example. I looked
> at those capacitors and I wondered how I was going to get them out.

Patience, good eyesight, a steady hand and a narrow soldering pencil.
Removal isn't quite as tricky as replacement with the radial caps. The one
thing to keep in mind is that the SMD pads cannot take any lateral stress
with leaded components or breakage will surely result.

During installation of the new caps, they must be positioned against the
headphone jack while heating/soldering with a pencil. Then, a hot glue gun
is used to bond the caps against the headphone jack. The caps cannot be
"straightened" after heating or the pads will lift.

Paul, W9AC

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Mike Harris-9

Re: K3 Audio Low Pass Filter

In reply to this post by Brett Howard

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

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Brett Howard

Re: K3 Audio Low Pass Filter

In reply to this post by P.B. Christensen

There has to be a set of SMT caps that will fit back down onto those
pads... Has anyone looked for that yet? If there isn't a set of caps
that fit those pads with the right specs then that means that Elecraft
had to spin the board when they started putting those caps in there.

~Brett

On Fri, 2009-07-03 at 18:37 -0400, Paul Christensen wrote:

> > I would like to consider making more audio modifications, the one changing
> > headphone audio coupling capacitors to larger values for example. I looked
> > at those capacitors and I wondered how I was going to get them out.
>
> Patience, good eyesight, a steady hand and a narrow soldering pencil.
> Removal isn't quite as tricky as replacement with the radial caps. The one
> thing to keep in mind is that the SMD pads cannot take any lateral stress
> with leaded components or breakage will surely result.
>
> During installation of the new caps, they must be positioned against the
> headphone jack while heating/soldering with a pencil. Then, a hot glue gun
> is used to bond the caps against the headphone jack. The caps cannot be
> "straightened" after heating or the pads will lift.
>
> Paul, W9AC
>

Brett Howard

Re: K3 Audio Low Pass Filter

In reply to this post by Mike Harris-9

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
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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Bob Cunnings NW8L

Re: K3 Audio Low Pass Filter

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<[hidden email]> 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
>>
>> ______________________________________________________________
>> 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]
>
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>

Geoffrey Mackenzie-Kennedy

Re: K3 Audio Low Pass Filter

In reply to this post by Mike Scott-7

Mike,

The method that I use to clear holes in pcbs that are filled with solder is
similar to pushing a heated wire through the hole, but I use a sewing needle
instead because solder will not stick to a needle. As you did with with the
wire, keep heating the needle with an iron while pushing it gently down
through the hole, until some of the needle passes through the hole.You will
have to get rid of any "blobs" of solder that fall out during the process of
course.

Working in close quarters is not difficult with this method

I keep a number of sewing needles of different diameters/ lengths at hand
for this purpose which I "borrowed" temporarily from my XYL many years ago,
and to some of them I have added a small diameter grip at the thread end, so
that I can hold the needle by hand when I do not want to use needle nose
pliars.

It is a good idea to keep Vias open and not filled with solder, otherwise
they may not function properly in some cases, but be careful not to damage a
Via when removing solder.

73,
Geoff
GM4ESD

Mike Scott wrote on Friday, July 03, 2009 at 9:04 PM:

>I just completed an installation of the K3 audio low pass filter board, the
> one Lyle put out to individuals who wanted to try it. I was busy until now
> as the boards came out some time ago.
>
> It took a lot longer than expected because all the K3 DSP board holes were
> full of solder. The instructions seemed to indicate that four of the holes
> should have been clear, i.e., just stick the leads through. The
> instructions
> seemed to be missing a section though as they never suggested soldering
> four
> of the wires. I thought maybe a page was missing but the step numbers
> didn't
> seem to indicate missing steps. Anyway, solder wick and solder suckers
> didn't work. The holes are very small and it is tight quarters where a
> miscue of the soldering iron could cause damage. I finally had to heat the
> wire I wanted to put in the holes (resistor leads) and heat my way through
> the soldered holes.
>
> For future reference, what would be the right way to do this?
>
> I would like to consider making more audio modifications, the one changing
> headphone audio coupling capacitors to larger values for example. I looked
> at those capacitors and I wondered how I was going to get them out. The
> solder leads on one side seemed to be down at the bottom of a narrow
> canyon
> caused by interfering components.
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1 #1311

Brett Howard

Re: K3 Audio Low Pass Filter

In reply to this post by Bob Cunnings NW8L

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<[hidden email]> 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
> >>
> >> ______________________________________________________________
> >> 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
> >
> ______________________________________________________________
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Joe Subich, W4TV-4

Re: K3 Audio Low Pass Filter

> 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: [hidden email]
> [mailto:[hidden email]] 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<[hidden email]>
> > 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

P.B. Christensen

Re: K3 Audio Low Pass Filter

In reply to this post by Mike Scott-7

> There has to be a set of SMT caps that will fit back down onto those
pads... Has anyone looked for that yet? ~Brett

I've looked. The problem is in getting more than 100 uF of C in the given
PCB real estate with SMT components. At 220-330 uF, radial caps are
required, unless Elecraft was to redesign the PCB.

As much as I like the new low-end warmth, I'm in the minority. Many folks
detest bass response in a communications receiver and I completely respect
that. In all fairness to Elecraft, I wouldn't change the PCB layout to
accommodate the caps unless it was part of some other re-design work.

Paul, W9AC

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Merv Schweigert

Re: K3 Audio Low Pass Filter

Is stacking 2 high possible to get enough cap?

Merv KH7C

>> There has to be a set of SMT caps that will fit back down onto those
>>
> pads... Has anyone looked for that yet? ~Brett
>
> I've looked. The problem is in getting more than 100 uF of C in the given
> PCB real estate with SMT components. At 220-330 uF, radial caps are
> required, unless Elecraft was to redesign the PCB.
>
> As much as I like the new low-end warmth, I'm in the minority. Many folks
> detest bass response in a communications receiver and I completely respect
> that. In all fairness to Elecraft, I wouldn't change the PCB layout to
> accommodate the caps unless it was part of some other re-design work.
>
> Paul, W9AC
>
> ______________________________________________________________
> 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

Re: K3 Audio Low Pass Filter

In reply to this post by Joe Subich, W4TV-4

I could be wrong... I'll have to take a closer look... Or I guess I
could just take some audio measurements of the headphones port.

~Brett

On Fri, 2009-07-03 at 21:37 -0400, Joe Subich, W4TV wrote:

> > 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: [hidden email]
> > [mailto:[hidden email]] 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<[hidden email]>
> > > 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
>
>
>

Brett Howard

Re: K3 Audio Low Pass Filter

In reply to this post by P.B. Christensen

I've been informed Elecraft is already replacing those caps with 100uF
caps in the current production units.

~Brett

On Fri, 2009-07-03 at 21:50 -0400, Paul Christensen wrote:

> > There has to be a set of SMT caps that will fit back down onto those
> pads... Has anyone looked for that yet? ~Brett
>
> I've looked. The problem is in getting more than 100 uF of C in the given
> PCB real estate with SMT components. At 220-330 uF, radial caps are
> required, unless Elecraft was to redesign the PCB.
>
> As much as I like the new low-end warmth, I'm in the minority. Many folks
> detest bass response in a communications receiver and I completely respect
> that. In all fairness to Elecraft, I wouldn't change the PCB layout to
> accommodate the caps unless it was part of some other re-design work.
>
> Paul, W9AC
>
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KK7P

Re: K3 Audio Low Pass Filter

In reply to this post by P.B. Christensen

>> There has to be a set of SMT caps that will fit back down onto those
> pads... Has anyone looked for that yet? ~Brett

Current production radios use 100 uF capacitors in those positions,using the
existing pads.

Lyle KK7P (on the road)
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Julian, G4ILO

Re: K3 Audio Low Pass Filter

In reply to this post by P.B. Christensen

P.B. Christensen wrote

As much as I like the new low-end warmth, I'm in the minority. Many folks
detest bass response in a communications receiver and I completely respect
that. In all fairness to Elecraft, I wouldn't change the PCB layout to
accommodate the caps unless it was part of some other re-design work.

This is described as a low pass filter, so presumably it cuts some of the highs rather than increasing the lows. I think I'm missing the point of this modification. What does this achieve which centering the IF passband at 1.4KHz or lower instead of 1.5KHz or using the RX EQ settings doesn't?

Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

P.B. Christensen

Re: K3 Audio Low Pass Filter

In reply to this post by Brett Howard

> I've been informed Elecraft is already replacing those caps with 100uF
> caps in the current production units.

100 uF is the maximum size compatible with the existing PCB pads for C9/C13
on the main DSP Board. Moving up beyond 100 uF presents a problem. Even at
100 uF, I believe the SMT caps are now rated at close to 10 WVDC. There's
just no more scaling back on the SMT cap's voltage rating in order to
accommodate a fit with a higher C value above 100 uF.

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. Anyone wanting to take full
advantage of the lowest vocal fundamental (e.g., AM or ESSB modes) wants
that point down to ~ 70 Hz. So, a cap value of 220 uF would be preferred.
I went to 330 uF in a radial style to allow extra margin for a wide range of
headphone vintages and types. To make most use of the 100 uF coupling caps,
I would ensure that my headphones are of the newer, medium Z type and not
the older style with 4-8 ohm drivers.

My guess is that scaling the caps beyond 100 uF is only of interest to a
small minority of ops. The majority will probably be happy with the current
choice of 100 uF. Going from 10 uF in the prior design to 100 uF is already
a significant step in the right direction.

Paul, W9AC

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Alan Bloom

Re: K3 Audio Low Pass Filter

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

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