[Elecraft] [K3] K3 Rev C DSP with Low Freq Enhancement

[lyle johnson]

Let me try and eliminate the confusion.

1) The low frequency response is constrained by two things: the audio path 
components, and the various filters (roofing filter, DSP IF filter and DSP 
audio filter (including Rx Equalizer).

2) Several months ago, there were circuit component changes made to the DSP 
board to improve Tx and Rx low frequency response.  The Rx path that was 
changed was the headphone path -- 10 yF output capacitors were changed to 100 
uF capacitors.  There was no need to change components in the speaker or Line 
Out circuitry.

3) At the time these capacitors were changed, *other* component changes were 
made to improve the *transmit* audio low frequency response.  Several 
components were changed to improve this response for the front panel 
microphone, rear panel microphone, and line input paths.

4) With these changes, the receive low frequency response was now limited by 
the various filters (roofing filter, DSP IF filter and DSP audio filter).

5) The firmware in the K3 sets up the filters for maximum "communications" 
effectiveness, making the nominal low frequency roll-off around 200 Hz.

6) The latest beta test firmware *allows* you to move the combined *filter* 
response lower, improving low frequency fidelity if you so desire.  This will 
affect all the possible receive paths: speaker, headphones and line out.

73,

Lyle KK7P/7 (vacationing in Tucson AZ)