K2 Audio issue

[Bob Wehking]

I have a K2/100 & an Icom 756Pro. I am trying to use a switch box to switch a Icom SP-21 8 ohm speaker between rigs. When I have the K2/100 connected to the SP-21 I have to turn the audio control way up to hear anything, but when I switch back to the Icom radio its audio output is OK. Is this due to the fact that the K2/100 has a 4 ohm output & the Icom has an 8 ohm output?

Bob
WB8DDI
K2/100 # 4998
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[Don Wilhelm-3]

Bob,

Your biggest problem is the 8 ohm impedance Icom speaker.  Most solid state
power amplifiers will deliver more power into a lower impedance load - the
K2 audio power output spec is for 1 watt max into a 4 ohm load - when the
audio output amplifier tries to work into an 8 ohm load, the power will be
reduced substantially - likely only 1/4 watt will be available.

The other part of the equation is the Sound Pressure Level (SPL) of the
speaker - that varies from one speaker to another.  The SPL of the K2
internal speaker is higher than normal (in part as compensation for the
relatively low audio power available), and while I do not know the SPL for
your Icom speaker, I would wager that it is not as high as the K2 internal
speaker, and therefore not as loud for the same driving power.

As stated many times by Wayne B., the K2 design criteria was for low receive
current consumption and that is one reason that the K2 has limited audio
power output.  The current consumed by a higher powered audio stage could
likely take more current than the rest of the receiver.

Those of us who want loud audio in the shack would do well to consider using
an external audio amplifier - at least that is the solution for me.

73,
Don W3FPR

> -----Original Message-----
>
> I have a K2/100 & an Icom 756Pro. I am trying to use a switch box
> to switch a Icom SP-21 8 ohm speaker between rigs. When I have
> the K2/100 connected to the SP-21 I have to turn the audio
> control way up to hear anything, but when I switch back to the
> Icom radio its audio output is OK. Is this due to the fact that
> the K2/100 has a 4 ohm output & the Icom has an 8 ohm output?
>
> Bob
> WB8DDI
> K2/100 # 4998
>

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[Darwin, Keith]

If the K2 can do 1 watt into 4 ohms I'd expect it would do 1/2 watt at 8
ohms, not 1/4.  The drop in volume from 4 ohm to 8 ohm should be small.
Noticeable, but small; assuming of course the efficiency of the two
speakers is similar.

If you're seeing a big drop in volume between the two rigs are you sure
it isn't the switch?  Do you get the same low output with the Icom
speaker connected to the K2?  If you swap the rigs on the switch does
the low output suddenly move to the Icom rig?  

- Keith -

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Don Wilhelm
Sent: Friday, December 02, 2005 10:34 AM
To: Bob Wehking; [hidden email]
Subject: RE: [Elecraft] K2 Audio issue

Bob,

Your biggest problem is the 8 ohm impedance Icom speaker.  Most solid
state power amplifiers will deliver more power into a lower impedance
load - the
K2 audio power output spec is for 1 watt max into a 4 ohm load - when
the audio output amplifier tries to work into an 8 ohm load, the power
will be reduced substantially - likely only 1/4 watt will be available.

The other part of the equation is the Sound Pressure Level (SPL) of the
speaker - that varies from one speaker to another.  The SPL of the K2
internal speaker is higher than normal (in part as compensation for the
relatively low audio power available), and while I do not know the SPL
for your Icom speaker, I would wager that it is not as high as the K2
internal speaker, and therefore not as loud for the same driving power.

As stated many times by Wayne B., the K2 design criteria was for low
receive current consumption and that is one reason that the K2 has
limited audio power output.  The current consumed by a higher powered
audio stage could likely take more current than the rest of the
receiver.

Those of us who want loud audio in the shack would do well to consider
using an external audio amplifier - at least that is the solution for
me.

73,
Don W3FPR

> -----Original Message-----
>
> I have a K2/100 & an Icom 756Pro. I am trying to use a switch box to
> switch a Icom SP-21 8 ohm speaker between rigs. When I have the K2/100

> connected to the SP-21 I have to turn the audio control way up to hear

> anything, but when I switch back to the Icom radio its audio output is

> OK. Is this due to the fact that the K2/100 has a 4 ohm output & the
> Icom has an 8 ohm output?
>
> Bob
> WB8DDI
> K2/100 # 4998
>

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[Vic K2VCO]

Bob Wehking wrote:
> I have a K2/100 & an Icom 756Pro. I am trying to use a switch box to
> switch a Icom SP-21 8 ohm speaker between rigs. When I have the
> K2/100 connected to the SP-21 I have to turn the audio control way up
> to hear anything, but when I switch back to the Icom radio its audio
> output is OK. Is this due to the fact that the K2/100 has a 4 ohm
> output & the Icom has an 8 ohm output?

Make sure you are using the external speaker jack on the back of the K2
and not the headphone jack.  The 'phone jack has resistors in series
with it and will produce less output into a speaker.  Also it's a stereo
jack, and plugging a mono plug into it will in effect make the
abovementioned resistors into a voltage divider which will halve the
available output.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Paul Heller-2]

>As stated many times by Wayne B., the K2 design criteria was for low
>receive current consumption and that is one reason that the K2 has
>limited audio power output.  The current consumed by a higher powered
>audio stage could likely take more current than the rest of the
>receiver.
>
>Those of us who want loud audio in the shack would do well to consider
>using an external audio amplifier - at least that is the solution for
>me.
>
>  
>

For what it's worth, the K2 here works very well with the Sounds Sweet
speaker (and yes, it does seem out of proportion somehow that the
speaker is many times the size of the K2, but it does produce lots of
audio ;-)  ).

Having said that, I prefer phones for CW and use phones 95% of the time,
but the speaker works well when I'm in the mood for it.

--

 /Paul Heller
  W3PH

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[John Magliacane]

--- Don Wilhelm <[hidden email]> wrote:

> As stated many times by Wayne B., the K2 design criteria was for low
> receive current consumption and that is one reason that the K2 has
> limited audio power output.  The current consumed by a higher powered
> audio stage could likely take more current than the rest of the receiver.

For a linear, class AB audio amplifier, I would agree.  However, there are some
very efficient Class D audio amplifiers on the market now that deliver an
amazing amount of audio power from very tiny packages.

Check out:

         http://monolithicpower.com/prd_05_classd_amp.htm

They have a 20-watt amplifier in an 8-pin DIP package.  It's rated at 24 volts,
and can operate down to 9.5.  The quiescent current at 24 volts is a whopping
1.5 mA, and efficiency is 93% at 20-watts!  (I'd assume the power output at 12
volts into 4 ohms is 20/4, or 5 watts.)

The challenge, of course, will be in preventing the switching noise from the
amplifier from destroying the noise-floor of an already very quiet receiver.

As far as getting more volume from an 8-ohm speaker, there may be small 4-to-8
ohm matching transformers available that can do the trick.  An old audio output
transformer with 4 and 8-ohm taps on its secondary can be wired as an
autotransformer to achieve a similar effect.


73, de John, KD2BD


Visit John on the Web at:

        http://kd2bd.ham.org/
.
.
.
.


               
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