[Elecraft] This thing rocks!

[Tom Hammond NØSS]

Dan:

>One bitch is the sidetone is ugly. Anyone got a cleanup for the nasty 
>harmonics on the sidetone? It's hard to zero-beat if it's not a clean tone.

This one works... note that even if you don't have the EXACT values... even 
something relatively close will work.

THANKS to Randy Hargenrader, WJ4P, for this one!


   From: "Randy Hargenrader" <randyh@harksystems.com>
   To: <elecraft@qth.net>
   Subject: [Elecraft] SINEWAVE SIDETONE
   Date: Sat, 26 Feb 2000 02:26:53 -0500

   K2'ers,

   Tonite I finally cracked the sidetone "nut"! I now have a pure
   sinewave from the sidetone circuit working in serial numbers
   183 and 661. It's VERY easy. Here's the modification to the
   control board...

   1) Add a 47 K ohm resistor to the position of C24, a .0027uF
   capacitor. Pull up one side of C24. It doesn't matter which
   side. I had to completely remove it first then extend one lead
   out from the body of the capacitor so that it would have one
   lead in a hole and one lead up in the air for a "flying
   connection". Add the 47K ohm resistor to the other hole, also
   standing on end. Tack solder the top of the 47K ohm resistor to
   the "top" lead of C24, making a "flying" connection. Note: If
   the only modification you make is to add the 47K resistor, the
   tone will smooth out enough that you WILL notice a difference
   (for the better) but the tone will not be a clean sine wave.
   The next step will give the sine wave.

   2) Make sure C33 is a 2.2uF electrolytic capacitor. (If you
   made the previous modifications to the sidetone I suggested
   some time ago, you might want to use these new values.) Solder
   a 47mH inductor across pins 7 and 10 of RP5. Do not remove RP5,
   and there is no need to cut any traces. Just tack solder the
   47mH inductor across pins 7 and 10 of RP5. Note: For those of
   you who prefer to run low frequency sidetones, the sidetone
   begins to become slightly distorted below 530Hz and loses the
   nice sinewave shape below that. To compensate, use a 4.7uF cap
   at C33 or tack a 2.2uF cap across it on the back of the board.
   The higher frequency side-tones will be nice but at a slightly
   lower amplitude which isnt really a problem since you can reset
   the level at will.

   Your done! Put your K2 back together and start enjoying the
   sweet sound of a sine wave sidetone!

   BTW, miniature 47mH chokes are available from Mouser
   Electronics - part number: 434-03-473J, at 800 346 6873.
   Approximate cost $1.36 each. Usual disclaimers...

   72,
   Randy WJ4P

73 - Tom Hammond   N0SS