[Elecraft] K2 - SSB TX audio

[ON4WIX]

Hi all,

another day, another question it seems...

I finished building the KSB2 board yesterday and installed it in my K2 s/n 5361.
All test results were OK. I changed the BFO settings as per the manual instructions.

This morning I made a recording of my transmissions. The K2 is hooked up to a dummy load, receive audio is fed from my TS-570 into the computer. The soundcard is not overloaded, checked that by recording a few signals off air with my TS-570.

I noticed that my audio sounds very 'gritty'. RF out reading seems OK on the K2, ALC is just flashing 1 LED.
Speaking about 2 inches from the mic it seems the audio is cutting out in a very rapid fashion. It sounds like a noise gate switching on and off very quickly. This causes sibilants to sound almost as white noise. Speaking into the microphone very closely (lips touching mike) the noise gating effect is much less pronounced.

I read that the KSB2 compressor chip also has a noise gate. This makes me wonder whether there is not enough drive from the microphone, resulting in an audio level that's right on the threshold of the noise gate. Do I need to crank up my mic audio before it enters the K2? I do have a simple 741-based preamp lying around somewhere but I'm a bit hesitant to press it into service sitting next to a transmitter.

Microphones used for this test were a Kenwood hand mike (the one originally supplied with my TS-570) and a Heil BM-10 with an HC-5 cartridge. Both exhibited similar behaviour.
I recorded my tests with these two mikes. If anyone wants to receive these recordings in order to evaluate the problem please send me a mail direct. Address is <mycall>@skynet.be

I have not tweaked the BFO frequencies for optimal audio yet. It would seem to me that this is not a BFO/bandpass filter related problem given the choppy audio. It's not really a problem that's situated in the frequency domain.

Anyone had a similar experience?

Have a very nice Sunday

73 de Glenn ON4WIX