[Elecraft] K3: Low speaker output problem

Wed Sep 8 10:13:03 EDT 2010

I have a pair of Radio Shack Minimus-7 speakers which I've had for 20
or 30 years.  They have wonderful fidelity for speakers of that size.
For a long time I used a 30 watt stereo amp to drive them.  What the
Minimus-7 does NOT have is any degree of efficiency.  They are, in a
word, spectacularly NON-efficient.  I'm not going to throw them away
by any means, but I will keep a amp in front of them.  The amp I had
was a very 1960's design driving an output transformer matching the 8
ohm impedance with a rating of 30 watts per channel.

I was not able to get adequate volume out of the Minimus-7 when I put
them behind the K3.  Replacing them with Radio Shack Optimus XTS-25, I
can raise the K3 volume to intolerable levels.  There is nothing WRONG
with the Minimus-7, they simply require power to drive them, and were
designed to go behind forty watt amplifiers.

The point is that speakers have WILD variation in efficiency, that is
to say the voltage required on the speaker terminals to produce a
fixed sound pressure in front of the speaker.  In some cases
inefficiency is DELIBERATELY used to smooth response, sometimes having
sound-absorbing, (therefore efficiency reducing) insulation inside the
case to dampen case resonances, and deal with other issues that work
against smooth frequency response.

**** It is for sure that there are some speakers which the K3 will not
drive adequately. ****

Before tearing apart your K3 looking for burned resistors, etc., see
if the speaker is one of those with deliberately engineered,
on-purpose low efficiency rated for higher wattage.  If you have a
small speaker with multiple internal cones, a crossover, and rated at
50 watts, you most likely will not be able to drive it with your K3.

73, Guy.

On Wed, Sep 8, 2010 at 12:07 AM, Tim Tucker <ae6lx at worldwidedx.com> wrote:
> Because of this thread I decided to do a quick comparison of my K3 to
> another rig.  I have the W2IHY iPlus hooked up to both the K3 and 746 Pro
> using the Icom SP-21 speaker.  For those that aren't familiar with the
> iPlus, it allows you (among other things) to switch your audio stack and
> output speaker between two rigs.  I switched both rigs back and forth on
> some strong 75m stations tonight with both rigs' NB and NR turned off and RF
> gain turned to max on each.  Both rigs AGC were set to slow for posterity's
> sake.  I'm using the proper speaker cables on both rigs running to the iPlus
> switch and then from the iPlus to the SP-21.
>
> I tested the entire AF range of both rigs which switching back and forth on
> the same RX stations.  The results of this test show me that the Icom 746
> Pro audio output is significantly greater than the K3.  I don't have any
> test equipment to measure this, but I could probably make an audio recording
> if desired.  The K3's audio wasn't too low and was generally very
> comfortable, but the 746 Pro did have more output potential if desired.  I
> could see how the greater volume potential would be desired by those who are
> hard of hearing.  Keep in mind that this test is using a MONO speaker.  I
> could do the test again using some stereo headphones output from the iPlus
> if there is any interest.
>
> Tim
> AE6LX
>
> On Tue, Sep 7, 2010 at 8:35 PM, Joe Subich, W4TV <lists at subich.com> wrote:
>
>>
>> Dave,
>>
>> Check to confirm that you are using a 3.5mm plug on your speaker
>> cable and not a 1/8" plug.  The difference is slight *BUT* it can
>> cause the "sloppy fit" behavior you are seeing.
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>>
>> On 9/7/2010 7:50 PM, David Lankshear wrote:
>> > I've had several bouts of no output and a couple of low output from
>> > my K3 #1122.  It's been down to the speakers jack socket seemingly
>> > being a very sloppy fit with every one of several changes of jack
>> > plug.
>> >
>> > I thought I'd tamed it by taping the speaker wires to another firmly
>> > secured cable in the hope that would keep all well and truly
>> > together, but on switching on after a few weeks of lack of use, my
>> > outboard speakers were "at it" again, and a good wiggling of the jack
>> > plug was required to alleviate the problem.
>> >
>> > I don't know if this is a common problem or a unique one, but it is a
>> > minor irritant, especially if one speaker goes out and then comes
>> > back on as the other goes off.  I kind of "wobble" on my chair when
>> > that happens HI!
>> >
>> > 73 all.  Dave  G3TJP
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