[K3] Shorting K3 PHONE jack outputs (WAS OT: Stereo to mono adapters)

[Don Wilhelm-4]

  James,

The only way to be certain is to examine the schematic of the adapter (I
know, sometimes that is hard to come by), or to dope it out with your
ohmmeter.  I have found some that do it either way.

The one you want is one that connects the ring and tip of the stereo
plug to the tip if the mono jack.  That one will connect both the left
and right channels together and do what you desire.

Sorry if the adapter nomenclature is confusing - in the midst of
confusion and lack of information about how the various adapters are
wired, it is usually easier to build your own adapter rather than
relying on the "smarts" of someone else who assumes (but does not know)
what you are trying to accomplish.

73,
Don W3FPR

On 12/3/2010 11:53 PM, James Sarte (K2QI) wrote:

> BTW, one thing I noticed is that both stereo to mono adapters I
> purchased short ring and tip together rather than ring to sleeve.
> Since both hot signals are combined, isn't there still a load being
> presented to the right channel amp?
>
> I know some adapters will short ring to sleeve, thereby presenting a 0
> ohm load to the amp.  In this case, that isn't happening.
>
> My ohm meter shows when using a stereo to mono adapter while connected
> to the mono DSP, ring and sleeve show a 22 ohm load; tip and sleeve
> show a 22 ohm load, and ring and tip have a 1 ohm load as they're
> shorted.
>
> Seems safe to me?
>
> Tnx,
> James K2QI
>
>
>
> On Fri, Dec 3, 2010 at 6:14 PM, Paul Christensen<[hidden email]>  wrote:
>> Jim (K9YC) is right.  When looking at the K3 schematic, realize that the
>> headphone amp's 8-ohm build-out resistors are not on the same schematic page
>> as the headphone amp.  At least it wasn't the last time I looked.
>>
>> Paul, W9AC
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[K2QI]

Hi Don,

No such luck on finding schematics for the adapters, but I did test
everything out with my ohmmeter.  It looks like the adapters I
purchased do exactly what you suggest.  Ring and tip of the adapter is
connected to just tip on the other end of the mono cord, while sleeve
are shorted on both ends.

Seems to work well enough, and as I said in my previous emails, both
tip and ring present the K3 with a 22 ohm load when connected to the
ANEM.

Only thing I have to figure out now is what to do about the audio
being out of phase; there is a hollow, echo type sound that is
produced now that both channels are being combined into a single
channel.

73,
James K2QI

On Sat, Dec 4, 2010 at 1:10 AM, Don Wilhelm <[hidden email]> wrote:

>  James,
>
> The only way to be certain is to examine the schematic of the adapter (I
> know, sometimes that is hard to come by), or to dope it out with your
> ohmmeter.  I have found some that do it either way.
>
> The one you want is one that connects the ring and tip of the stereo plug to
> the tip if the mono jack.  That one will connect both the left and right
> channels together and do what you desire.
>
> Sorry if the adapter nomenclature is confusing - in the midst of confusion
> and lack of information about how the various adapters are wired, it is
> usually easier to build your own adapter rather than relying on the "smarts"
> of someone else who assumes (but does not know) what you are trying to
> accomplish.
>
> 73,
> Don W3FPR
>
>

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[K2QI]

Aha! Discovered that AFX was on.  Turned it off, and now everything
works perfectly.

73 and good night!
James K2QI

On Sat, Dec 4, 2010 at 1:28 AM, James Sarte (K2QI) <[hidden email]> wrote:
> Only thing I have to figure out now is what to do about the audio
> being out of phase; there is a hollow, echo type sound that is
> produced now that both channels are being combined into a single
> channel.
>
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[Phil Salas]

"...I'd really like to find some affordable shielded dual center conductor
stuff somewhere.  ..."

I use All Electronics S-videa cable for many of my applications (I cut off
the connectors and use the cable).  These cables consist of two individually
shielded cables in one overall cable.  I bought their CB-285 S-video cable
that is 100-feet long so I'd have plenty.  But they also sell 12-, 25-, and
50-foot chunks of it.

Phil - AD5X

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[P.B. Christensen]

James,

You just discovered that some mono phase cancellation will occur when
combining two audio channels with AFX engaged.  That's normal.  The effect
is the same as when two channels on an analog tape deck are combined, and
those two channels are not phase coherent.  If the tape heads are not
aligned to within a small degree, phase cancellation occurs beginning with
the high frequencies, then begins to comb-filter with greater misalignment.

I've not done this, but it would be interesting (and cool) to look at the
K3's headphone audio into a scope using the Lissajous method.

http://www.jmargolin.com/mtest/LJfigs.htm

Left ear channel to the vertical Y input, right channel to the horizontal X
input.  With AFX disengaged, there should be a straight 45 degree line on
the display.  Then, with AFX engaged, what will be seen is a fuzzy oblong
ball that reflects the deliberate phase change (the reason for AFX!) between
left and right channels.  Any deviation from a straight line shows the
degree of phase change.  The reason for the 45 degree line is that equal
amplitude/phase from left and right inputs places the line between both X
and Y axis.  If only left channel audio is monitored, you get a straight
vertical line.  Right channel only?  A flat, horizontal line is shown.

Looking at the K3 schematic, when both headphone channels combine into your
22 ohm ANEM source Z, each channel sees about 14 ohms.  I Thevanized the
inputs and outputs and got that value.  What's interesting is that with AFX
engaged, one headphone amp channel may be going negative while the other is
going positive.  Also, there's little isolation between outputs with the 8
ohm resistors separating channels.  I doubt this is a concern, but the
National Semiconductor datasheet doesn't address instability concerns with
resistively combined output channels.  Myself, I see no problem with it as
you have it configured.

Paul, W9AC

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