After getting an Elecraft K2, I immediately fell in love with many of the features and the filtering. But one thing that kinda made operating it unpleasant was the harsh sounding cw side tone. Being an Elecraft kit, I knew there had to be a mod.

So I looked around the net and found a page that described a modification to the control board which only required 3 components to be tack-soldered to the board. A 47K Ohm resistor, a 2.2uF capacitor, and a 47mH inductor.. So for less than $2.00 a pure sine wave side tone could be had .. Since I couldn’t find any pictures of the mod, I decided to share what I did with full pics and description.


Doing the Mod:

I happened to have a resistor and cap of the right values in my parts bin, but no inductor. I had to order the 47mH inductor from DigiKey – Part number 811-1290-ND – price: $0.84 and it is very important that you get the inductor with higher impedance as recommended from KT5X (all links will be below.)

Pulling the board was simple (a task I’ve performed many times for repairs/mods,) and one trace had to be cut, but otherwise a simple modification to do, and as you will hear in the Mp3 file below, the results of this side tone mod are very dramatic. The Elecraft K2 side tone is now a pure sine wave and very smooth compared to before. Here are the steps…


K2 Side Tone Mod Step 1:

Remove the control board from the K2 and add a 47 K ohm resistor to the position of C24, a .0027uF capacitor. Lift one end of C24 and make a “flying” connection by inserting one end of the resistor into one of the holes from C24.


K2 side tone mod add resistor

Lift one end of C24 and add resistor. Solder the “flying” leads together.


K2 Side Tone Mod Step 2:

Solder the 47mH choke inductor in series with C33, the 2.2uF capacitor. You must cut the trace between C33 and U10. you can see the cut trace in my photo.. It looks like the board is scratched.

I used an exacto knive and cut in 2 places. Then lifted the piece of trace out. Use an Ohm meter to make sure that you’ve removed all of the trace and that you have no conductivity where you cut.

For the choke inductor, you can use DigiKey part number 811-1290-ND which has the proper resistance for the mod to have best effect.

K2 CW side tone mod

Cut trace between the leads of the inductor and solder choke inductor to board.


K2 Side Tone Mod Step 3:

Tack solder the 2.2uF capacitor between pins 7 & 10 on RP5.. Bend the legs on so that nothing shorts on the board.

K2 Side tone mod

Notice new capacitor on lower left (also shown above) Other parts/wires are from previous mods/updates that I did to the K2


K2 Side Tone Mod Step 4:

Re-assemble and enjoy! Here is an Mp3 of the major difference in the side tone after I did this mod.. you will see that it is well worth the effort.





TF3MA Side tone Mod

Important Notes on resistance value of inductor

Original Elecraft Mod (only for notes – Use TF3MA method instead)

73, Brian