[Elecraft] SP3 A/B Switch Problem (IK4EWX)

[Geert Jan de Groot]

>   I had the same problem about one years ago. I have two SP3 loudspeakers, on
> on each receiver or both speakers, ore one receiver with the K3S audio
> effects that use both loudspeakers.
> The switch scratched when changing channel and it attenuated the audio
> signals.

Keep in mind that the SP3 speaker switches only switch speaker signal.
You Cannot Switch A Small-signal With A Switch.
Switches need a little DC (1mA probably sufficient) to "burn clean" the 
contacts.

I suspect that a 10K resistor from the speaker output to +12V will cause 
the desired 1mA to do the cleaning.
Looking at the schematics, this isn't easy because R1 and R63 on the 
K3IO board are in the way. So, you need to add a bipolar capacitor in 
series, and resistors to +12V to make it happen. Don't be surprised if 
operating the switch will "click" a bit but 1mA is well within safe 
limits for the speaker.

If you don't want to do through this, disconnect the K3, connect the 
same 10K resistor and operate the switch a few times.

Elecraft isn't the only to make this design mistake - I have some Yaesu 
speakers that did suffer the same problem and that were remedied the 
same way.

Since the K4 comes with a SP4 speaker that looks similar - I wonder if 
this design issue was addressed for the K4?

73,

Geert Jan PE1HZG