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Audio Thump

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Jimmy Lee-4

Audio Thump

When I use headphones I have a" thumping" sound everytime I key the rig.
(seems worse on wide range headphones, lots of bass response really
shows this "thumping" sound) Is this common and what is the fix?
Thanks,
Jimmy, AE4DT
K2 #2832

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Sverre Holm

RE: Audio Thump

Do you have the KDSP2 in your K2?

There is an issue with it that gives a pop as you change to rx.

--
73,
Sverre

------------------
Sverre Holm, LA3ZA
www.qsl.net/la3za

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jimmy Lee
> Sent: 28. juni 2004 15:07
> To: [hidden email]
> Subject: [Elecraft] Audio Thump
>
>
> When I use headphones I have a" thumping" sound everytime I
> key the rig. (seems worse on wide range headphones, lots of
> bass response really shows this "thumping" sound) Is this
> common and what is the fix? Thanks, Jimmy, AE4DT K2 #2832
>
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> Elecraft mailing list
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> http://www.elecraft.com
>

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Doc-8

Re: Audio Thump

Is this an issue with earlier versions of the KDSP2? I hear no thump with
either the KDSP2 or KAF2.....or with out either installed.....
--
73 ditdit,

Doc YI9RVT/KE4RVT
Al Kut, Iraq
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----- Original Message -----
From: "Sverre Holm" <[hidden email]>
To: "'Jimmy Lee'" <[hidden email]>; <[hidden email]>
Sent: Monday, June 28, 2004 6:54 PM
Subject: RE: [Elecraft] Audio Thump

> Do you have the KDSP2 in your K2?
>
> There is an issue with it that gives a pop as you change to rx.
>
>
> --
> 73,
> Sverre
>
> ------------------
> Sverre Holm, LA3ZA
> www.qsl.net/la3za
>
>
>
> > -----Original Message-----
> > From: [hidden email]
> > [mailto:[hidden email]] On Behalf Of Jimmy Lee
> > Sent: 28. juni 2004 15:07
> > To: [hidden email]
> > Subject: [Elecraft] Audio Thump
> >
> >
> > When I use headphones I have a" thumping" sound everytime I
> > key the rig. (seems worse on wide range headphones, lots of
> > bass response really shows this "thumping" sound) Is this
> > common and what is the fix? Thanks, Jimmy, AE4DT K2 #2832
> >
> > _______________________________________________
> > Elecraft mailing list
> > Post to: [hidden email]
> > You must be a subscriber to post to the list.
> > Subscriber Info (Addr. Change, sub, unsub etc.):
> > http://mailman.qth.net/mailman/listinfo/elecra> ft Help:
> > http://mailman.qth.net/subscribers.htm
> > Elecraft
> > web page:
> > http://www.elecraft.com
> >
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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Lyle Johnson-7

RE: Audio Thump

Hello Doc!

> Is this an issue with earlier versions of the KDSP2? I hear
> no thump with either the KDSP2 or KAF2.....or with out either
> installed....

With some K2s operating QSK there have been reports of a pop or click at the
switchover to receive. It is related to the different delay through the DSP
versus no DSP. Mods have been worked out an published.

Note that this is not present on all K2s; it depends somewhat on the
individual characteristics of the FETs used in the K2 audio muting circuit.
See

http://www.qsl.net/la3za/K2/modAny.html#KDSP2

73,

Lyle KK7P

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Jimmy Lee-4

Re: Audio Thump

Lyle and all others,
I have done a poor job of explaining my problem. There is a low frequency sound just as the key is closed on ever single sound that is keyed. Does
not seem to be related to QSK.
Thanks,
Jimmy

Lyle Johnson wrote:

> Hello Doc!
>
> > Is this an issue with earlier versions of the KDSP2? I hear
> > no thump with either the KDSP2 or KAF2.....or with out either
> > installed....
>
> With some K2s operating QSK there have been reports of a pop or click at the
> switchover to receive. It is related to the different delay through the DSP
> versus no DSP. Mods have been worked out an published.
>
> Note that this is not present on all K2s; it depends somewhat on the
> individual characteristics of the FETs used in the K2 audio muting circuit.
> See
>
> http://www.qsl.net/la3za/K2/modAny.html#KDSP2
>
> 73,
>
> Lyle KK7P
>
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dmb@lightstream.net

Re: Audio Thump

In reply to this post by Jimmy Lee-4

Hello Jimmy,

I know exactly what you're referring to, and it is not due to the KDSP2,
or the KAF2. It is there on the bare-bones K2, although it is primarily
audible when using headphones capable of very wide frequency response. I
have several pairs of various models of Grado headphones, as well as a
pair of Beyerdynamic DT-990's, and the thump is noticeable on all. In
fact, I can also hear a 'click' as well as a thump.

I've been wanting to investigate this myself, but haven't found the time
to do so yet. I've temporarily reduced it to the point where it's a lot
less noticeable by placing the series combination of a 3.3 uF cap and
220 ohm resistor in line with the headphones, and shunting across the
headphones with a .47 uF cap. The series 3.3 uF will help to reduce the
'thump' by reducing the low-frequency response, and the shut .47uF will
roll off the high frequencies, thereby reducing the 'click'. It's still
not perfect, but it's a lot better than it was. You may have to play
with these values depending upon the characteristics, and impedance of
your headphones.

Of course a much easier solution is to just use a pair of cheap
headphones, similar to the ones that come with a portable cd player,
(especially since you're ruining the response anyway by inserting the
caps and resistor) but in my case the comfort level of the Beyerdynamics
is enough of a reason to go through the little bit of extra trouble.

73, Dale / WA8SRA

Jimmy Lee wrote:

>When I use headphones I have a" thumping" sound everytime I key the rig.
>(seems worse on wide range headphones, lots of bass response really
>shows this "thumping" sound) Is this common and what is the fix?
>Thanks,
>Jimmy, AE4DT
>K2 #2832
>
>
>

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Vic K2VCO

Re: Audio Thump

In reply to this post by Jimmy Lee-4

Jimmy Lee wrote:

> Lyle and all others, I have done a poor job of explaining my problem.
> There is a low frequency sound just as the key is closed on ever
> single sound that is keyed. Does not seem to be related to QSK.
> Thanks, Jimmy

I have experienced this with some (not all headphones). It is worse if
for some reason you plug the 'phones into the external speaker jack
instead of the headphone jack.

Also, I had a switching system which allowed me to switch the audio,
keying, and antenna between my K2 and another rig; I found that when I
used this, the thump was much worse! I suspect that the cable to the
'phones was close to the DC power cable of my K2/100 and the thump was
actually induced in the 'phone cable by the large current in the power
cable.

You can reduce the thump by putting a capacitor (I used back-to-back 4.7
uf electrolytics) in series with the 'phones. One pair of 'phones that
I have requires this even when plugged directly into the headphone jack
on the K2.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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