[CW] How do I get high-frequency cutoff from stereo headphones?

[George, W5YR]

Will, the honest answer to your problem is to simply wait until robs you of
those higher frequencies.  <:}

Seriously, you have the right concept in mind: reduce the higher-frequency
response of the headphones.

My experience has been that with the way that modern headphones are
constructed, it is difficult to "get into them" to make any changes. Even
the plugs are molded on with no access to the actual connections.

So, if your receiver provides no "tone control" for reducing high-frequency
audio response, then you either have to go into the radio with
modifications or use an external "black box" to do the job.

I strongly recommend the latter. There are any number of excellent DSP and
other audio outboard filters available - see QST ads. Most of these will
allow you to tailor the audio frequency range to you needs.

If you want to homebrew something, you can build your own black box which
can contain anything from a simple capacitor across the headphone jack
connections to full-blown filters. Lots of designs available in the ARRL
Handbook and related sources.

You can investigate this approach by wiring a plug to go into your receiver
phones jack to a phone jack into which you plug the headset. Now you have
the wiring exposed so that you can try different caps across the phones or
even see what effect a simple low-pass RC filter has.

A single cap would simply be wired with one connection of the cap to one
connection to the phones and the other to the other connection.
Technically, you should avoid using electrolytic or polarized caps, but you
may require a large value which might be obtainable only with a polarized
capacitor. 

The difficulty with working only with passive components lies in the
relatively low impedance level of most heaphones, which range from a few
ohms to perhaps several hundred ohms. A popular value for most inexpensive
stereo phones for CD players, etc. is around 32 ohms, I understand.

If you don't mind putting a few bucks into the project, I suggest that you
look into some of the filters offered commercially. Almost any of them will
do what you are seeking. Or, if you are a homebrew specialist, a simple
op-amp low-pass filter will help a lot.

Let us know how you make out!   <:}

72/73/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121  Kachina #91900556  IC-765 #02437

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googlyelmo@earthlink.net wrote:

> I remember, dimly, reading somewhere that you can cut hi-freq. response
> by adding a capacitor across the two headphone leads.  Am I correct in
> my recollection?  If so, does the *type* of cap matter [i.e. ceramic,
> mylar, mica, etc.]?  While I know that a bit of trial-and-error
> substitution probably will be involved here, what general value should I
> 
> be looking at trying?  Finally, exactly how should the cap be wired into
> 
> the 'phone circuit?  I think I remember reading that you simply solder
> one cap lead to each of the two phone wires, but please confirm/correct
> this.  Thanks.