My K3 also "thumps" with power on and off transitions. In my case, I use the SPKRS output to drive either a set of headphones (Yamaha CM-500 or Sony MDR-7650) or the inputs of an old Radio Shack SA-155 amplifier, depending on whether the headphones are plugged into my headphone box. Looking at the schematic, it's no mystery what causes the thump. It's the classic effect of having large value electrolytic coupling capacitors at the output of the audio amp. The increase in value of the coupling caps to extend LF response that was made fairly early in the product cycle would certainly exacerbate this problem. My K3 has the larger caps installed.
I wonder if the presence or lack of a transient pulse in individual situations could be a function of the DC resistance (or LF response) of the transducer connected to the audio output. In my case, the load impedance presented to the output of the amplifier is considerably higher than it would be if I used an 8 Ohm speaker. Higher load resistance gives a larger RC time constant, hence a longer and more objectionable pulse. Just a thought... 73... Randy, W8FN >>> Is there any way to stop the tooth rattling turn on and turn off thump >>> from the K3? It can't be good to have a blast of DC go through my external >>> speakers I jump every time this happens. >>> >>> K6CG ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
