[Elecraft] K2DSP puzzle

Brendan Minish [email protected]
Sat Jul 19 09:05:59 2003


Hi everyone,
         Firstly I want to say a big thanks to Lyle for being so quick off 
the mark with a mod to fix the pops.

The pops were caused by the K2's Mute circuit cutting sharply the RX audio 
when going into transmit. This doesn't happen without the DSP installed 
because the RX audio is faded out over a few cycles just before the mute 
comes on, presumably by the K2 changing over from RX to TX however with the 
DSP installed it takes a few mSec for audio to get though the filter so the 
k2's mute circuit comes on whilst there is still audio at full level coming 
out of the K2DSP, on occasion the mute cuts at or near the top of a cycle, 
this is when we hear a click or a pop at the start of the side tone

Now to explain a little how the mod works

the mod works by shaping the onset of the mute so that it no longer comes 
in sharply.

the resistor between /MUTE and Q6/Q7 sets the attack of the mute (in 
conjunction with C23) and the total resistance of both resistors sets the 
release time of the mute circuit (equivalent to R17 on the control board)

with 2x 1.5 M resistors the attack of the mute circuit is about twice as 
fast as the release

It may be worth playing slightly with these values as each K2 is probably 
going to be slightly different.

In my K2 this has solved the problem with pops and has not slowed the QSK 
speed down at all. this mod also sounds fine with the KAF installed.

The K2DSP is an impressive addition to the K2 for CW as well as SSB.


73
Brendan


At 00:10 19/07/2003, Lyle Johnson wrote:

>THIS IS NOT AN AUTHORIZED MOD!
>
>Parts required:
>
>2 each 1.5 megohm, 5%, 1/4 watt resistors (brown-green-green-gold).
>
>Remove the Control board from the K2.
>
>1) Remove R17 (3.3M orange-orange-green-gold).
>
>2) On the component side of the board, cut the trace between C23 and U6 pin
>17.
>
>3) On the solder side of the board, add a 1.5M (brown-green-green-gold)
>resistor from the pad of R17 nearer C23 to U6 pin 17.
>
>4) On the solder side of the board, add a 1.5M (brown-green-green-gold)
>resistor from the other pad of R17 to U6 pin 17.
>
>Reinstall the Control board in your K2.
>
>OLD               R17
>                  +------+
>    /MUTE------+--| 3.3M |----(Q7 Source)
>               |  +------+
>               |
>               +--- (Q6, Q7 Gates)
>               |
>             -----
>      C23    0.01 uF
>             -----
>               |
>               |
>            (earth)
>
>NEW               R17
>                  +------+
>    /MUTE------+--| 1.5M |----(Q7 Source)
>               |  +------+
>               |
>             +---+
>             |   |  new resistor
>             |   |  1.5M
>             |   |
>             +---+
>               |
>               |
>               +--- (Q6, Q7 Gates)
>               |
>             -----
>      C23    0.01 uF
>             -----
>               |
>               |
>            (earth)
>
>REMEMBER, THIS IS NOT AN AUTHORIZED MOD!
>
>73,
>
>Lyle KK7P
>
>
>
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