K3 - background hiss (noisy K3) - update

[bozidar]

Hi,
i have studied all the posts about this topic.
Seems, that is still, huge confusion about that, so i will try to formulate a problem on simply way:

With low impedance earphones plugged into the audio jack on the K3, you can hear a really annoying noise (hiss) even with the AF and RF volume set to zero(CCW). This audio hiss has a constant level, is added to the audible RF noise and can prevent one from hearing weak  signals on an otherwise quiet band.

That hiss has nothing to do with K3 receiver or settings - simply is permanent present.
This indicate that something must be wrong with earphones amplifier LM4811MM, and that is
odd, because LM4811MM seems to be an high quality chip, designed exactly to work with low impedance earphones , with a minimal amount of external components?
My question is:
is, in the mean time, known any hardware (or anything else) modification for that issue?

best regards,
Bozidar

Hello Bozidar,

I suspect that the issue may be particular to your particular K3. You did
not mention the S/N range of your radio, and I may be incorrect about this
but I think that very early K3's had an issue similar to this, that was
quickly resolved.

The S/N of my K3 is in the 58XX range, and I have never heard any of the
hiss that you describe. I have a pair of Grado SR225e headphones that have
an impedance of 32 ohms, and are very sensitive. I plugged them into the
Phones jack on the front of the K3, and with the AF gain control turned
fully CCW, there is no hiss or for that matter any sound at all.

It's possible that there is an issue with your AF Gain control/encoder.
You might want to use the built-in test that allows you to check the
encoder steps of the two AF gain and two RF gain controls that is
available from the CONFIG > SW TEST menu on the radio. This requires that
you first make sure that "Tech Mode" is enabled. To do so, go to CONFIG >
TECH MD and then turn your VFO-A dial so that "On" shows above TECH MD on
your K3. Then, rotate your VFO-B dial to navigate over to the "SW TEST"
menu option. Then slowly rotate your AF Gain control on the K3. You should
see the encoder steps (visible on your K3 display) increasing in number as
you rotate it clockwise, and decreasing in number as you rotate it CCW. In
my case, rotating the AF Gain control fully CCW shows a step of 2. If your
value is higher than that at fully CCW, perhaps your AF Gain encoder has a
problem.

73,

Dale, WA8SRA

> Hi,
> i have studied all the posts about this topic.
> Seems, that is still, huge confusion about that, so i will try to
> formulate
> a problem on simply way:
>
> *With low impedance earphones plugged into the audio jack on the K3, you
> can
> hear a really annoying noise (hiss) even with the AF and RF volume set to
> zero(CCW). This audio hiss has a constant level, is added to the audible
> RF
> noise and can prevent one from hearing weak  signals on an otherwise quiet
> band.*
>
> That hiss has nothing to do with K3 receiver or settings - simply is
> permanent present.
> This indicate that something must be wrong with earphones amplifier
> LM4811MM, and that is
> odd, because LM4811MM seems to be an high quality chip, designed exactly
> to
> work with low impedance earphones , with a minimal amount of external
> components?
> My question is:
> is, in the mean time, known any hardware (or anything else) modification
> for
> that issue?
>
> best regards,
> Bozidar
>

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[Ignacy]

I do not notice any hiss with K3 with any headphones. I noticed hiss with other radios.
Ignacy, NO9E

[bozidar]

Hi Dale,
tnx for interesting info - i have done this test and ranges on AF and RF knobs are 2-240, so no problem with that.
Yes it is an early K3, S/N 28xx.
I use Sennheiser CX 300-II ear-canal phones impedance 16 Ohm - maybe is this impedance too low,
but accordingly to the data-sheet for LM4811 that should not be the problem.
I simply dont know what that could be?
73,
Bozidar, S50BN

[VK7JB]

Hello Bozidar,

I have K3 #5102 and also well preserved high frequency hearing. I've had the same hiss on my K3 audio since it arrived from the factory. I've used a wide range of headphones, expensive and cheap, and it's present with them all. I discovered that the fix is to introduce some resistance into the audio line and I use a very small, outboard, stereo headphone volume control to do this. I bought several for a few dollars on eBay. I just dial in a very small amount of resistance(I've never actually measured how much) and the hiss is completely gone, with only a very small effect on the K3 audio volume which can be easily compensated for by a tiny increase in the AF gain control if you need to. I have the same hiss on my KX3 audio, which I manage in the same way.

FWIW, I have no hiss at all using the same headphones on my little KX1.

Hope that helps,
73,
John VK7JB

[bozidar]

Hallo John,

tnx for proposal, a will try with some attenuation.
Gary AB7MY from Elecraft have helped me with some interesting proposals too.
I completely agree with you, unfortunately mein KX3 showes the same behewior
(hiss when RF put on zero), but in contrary to my K3, this hiss disappeared when RF is more than 0,
so for normal work with KX3 this hiss has no meaning.
tnx for all responses
73,
Bozidar, S50BN

[Sullivan, Mike C]

Not sure this helps much other than knowing you are not alone.
I have had the same problem and fixed it exactly as John - VK7JB has - SN on my K3 is in the 800s.
I have checked my S/N ratio and it is at least as good as the spec.
My hearing has been checked here at work and I have been told that I have good hearing for anyone these days, and really good for an OF.
I would bet having a pair of good ear-plugs in my pocket from the age of 18 or so had a lot to do with it.
Just tripped 60 yesterday.

Mike Sullivan
Lockheed Martin, Denver
 73 WM0CW ..


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[Bob McGraw - K4TAX]

One spec pertaining to headphones, and one not realized in terms of the
importance, is sensitivity.   The more sensitive the headphones means it
takes less audio power to produce acoustic energy.  If a given signal
say a value of -25 dBv is applied, this signal may be heard with some
headphones and may not be heard with others.  Now, adding a series
resistor in effect reduces the apparent sensitivity.  In fact, it
reduces the available power to the headphones.  In the case of the -25
dBv signal, adding a resistor may reduce this value to -35 dBv, or below
the sensitivity threshold of the headphones.  All of this has little to
nothing to do with the impedance of the headphones.

In most instances, everyone's hearing decreases with age.  Other factors
that affect a diminished hearing is prolong exposure to noise or any
loud sounds.   A combination of sound level and time exposed are key
elements to diminished hearing.  Repeated exposure over a long period or
repetitive cycles will lead to permanent hearing loss.  And in many
cases this loss is so gradual over a period of years it is not realized
or acknowledged to exist.

 From my experience, the audiologist, after a hearing test said my
hearing was normal.  Now what he didn't say was "my hearing was normal
for a male of my age".    My wife complains that I don't listen to
her.   At least that's what I think she said.

73
Bob, K4TAX

On 9/30/2015 7:57 AM, Sullivan, Mike C wrote:
> Not sure this helps much other than knowing you are not alone.
> I have had the same problem and fixed it exactly as John - VK7JB has - SN on my K3 is in the 800s.
> I have checked my S/N ratio and it is at least as good as the spec.
> My hearing has been checked here at work and I have been told that I have good hearing for anyone these days, and really good for an OF.
> I would bet having a pair of good ear-plugs in my pocket from the age of 18 or so had a lot to do with it.
> Just tripped 60 yesterday.


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[Merv Schweigert]

630M has been very active and plenty of good signals on the band,
I use an "old" K3 with new Synth and BPF and it has been working
excellent,   output is 1MW driving a 100watt NJD technologies amp.

For the past week or more i have been able to decode signals from
VK3ELV and VK5ABN for hours at a stretch,  from 1130Z until sunrise
here at 1630Z.  Vk has also been copied as far as the west coast
and inland as far as Texas.
I also decoded the first JA to KH6 it appears the other nite and again
last nite.  ja1pkg
Stations are copied as far as the mainland east coast.  And this is with
solar storms and heavy QRN here in the Pacific.
I am using a standard realtec on board sound card in a old HP3130 and
getting decodes up to -32 on a regular basis.

If you have the slightest interest in the low bands and WSPR its time
to take a listen,  also 136KHZ has been active and activity is increasing
there as well,  check the online WSPR map and see the activity around
the world on LF 136khz and MF 474.2khz.

Dx is alive and well on 630 meters,  jump in and get your feet wet, but
remember you cannot transmit there as yet without a experimental
license,   but decoding and reporting WSPR is fine with your ham call.
Or if you get bit by the LF bug you can apply for experimental call sign
and operate, its easy to do.

73 Merv K9FD/KH6  WH2XCR
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