22 martie 2013

Kenwood HS-5 modification for Stereo

Yeap, I have a Kenwood HS-5 radio headphones. Nice, comfortable and impressive headphones.
But, there is a "but" here!
They are mono headphones.
One can ask  "Why stereo headphones on ham radio"?
Well, most of modern transceiver has a secondary receiver.
You can use this for listening in split pileups to maximize the chance for a QSO or, in heavy noise you cand use the second receiver as a "Brain DSP" helper.
On two receivers, the noise is different but the signal is the same. The ear-brain DSP will surely take the signal out of noise better than any IF-DSP found in the most expensive rigs!
I can use a HI Stereo headphones but these are special designed for radio communications and does not reproduce the signals below 300 Hz and above 4000 Hz, which means that they will simply reject all the other signal than voice. 

After a couple of years of just wondering how can I made them stereo, today I made it...

I take the time for photos, so, you can click on them to see it in full detail detail.

First thing is to carefully open the outer protection without ruin the plastic bezel. Use a screwdriver and gently remove the metal case.
There a re two tab-locks that keep that metal case to the plastic bezel.

Lift one first and gently separate the metal case; identify the exact position.

 The second one is at 180 degrees; use the screwdriver for that too!

 These tabs are delicate so don't mess with to much muscle on it!

As a generaly reccomandation, in these days, too much force means you didn't choose the right way.

After removing the metal case, you see that the black wire is common for both headphones. We will left this one in place.
The red and the white ones are on our "radar".

You may sold them separately without no other concern, just be careful to put some isolation on the solders.

In my pictures you will see some resistors.
These are two 240 Ohm resistor in paralell on each transducer.

The reason is that I wanted to reduce the hiss on the headphones when I listen at low volume. Seems that all major radio manufacturers made the same mistake on the audio chain. They tend to put a lot of amplification on the Audio PA stage so, at low volume, there is a lot of noise.
And not the band noise, just the stage inherent noise.
A good way to reduce it without modification on the radio is to listen to high volume; in this case, you need to reduce the sound pressure on the ears.
One way to achieve this is to put some resistors in series with the headphones!

Carefully solder the resistors (may be just one for each side, but has to be the same value - test before for comfortable audition) and put some isolation on them.
After that, place the metal case on the headphones and this is it!
Of course, you have to put a stereo jack on the other side of the cable...

A did a quick test on FT-2000 and the result is amazing! Worth trying this 30 minutes mod!

73 de Adrian, YO3HJV

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