[Elecraft] K2 Audio mod comment

[Dave Andrus]

Roelof:

Thanks for posting that--I'm going to try it.  I haven't been unhappy  
with my K2's rx audio, but I would like a bit more low-end response  
when listening to some SSB speech.  And yes, I do tend to prefer lower  
frequency CW pitch, so that would help as well.

73,

Dave K7DAA
http://www.k7daa.com

On Mar 28, 2008, at 10:11 AM, Roelof Bakker wrote:

> Hello All,
>
> Matti, TF3MA has suggested a mod for the K2 to improve the low  
> frequency audio response by increasing the value of C25 and C26.  
> Matti used 100 nF / 0.1 uF in parrallel to C25 and C26. I had some  
> 470 nF / 0.47 uF smd (1206) capacitors available and soldered  these  
> at the bottom side of the control board PCB. This is a very easy mod  
> and only requires one to remove the top cover and uninstalling the  
> control board.
>
> As a result it is now a joy to listen at a low pitch in CW mode.
>
> Thanks!
>
> Roelof Bakker, pa0rdt
>
>
> TF3MA wrote:
>
> But I discovered that my K2, had a rather limited low freq audio
> response. So I took a look at the schematic for the audio circuit in  
> the
> K2...
>
> The original low freq. cutoff (-3db) freq. is approx. 640Hz (with  
> KAF or
> DSP moduls installed) or 400Hz (with no audio moduls) determined by  
> C25,
> C26 and the 5kOhm volume control (and NE612 mixer impedance), to  
> extend
> the audio frequency response for the low freq. I put
> 0.1uF SMD across C25 and C26, extending the low frequency response to
> approx. 320Hz. This improves the SSB sound of the receiver, and  
> improves
> SNR when copying low pitch CW signals. This simple mod increases the  
> rx
> audio signal at 300 Hz by about 3dB.
>
> -- 
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