G'day, Perhaps someone suitably qualified and tooled up might like to try and replicate and comment upon the view presented by Rob Sherwood at the Dayton convention. According to him the K3 audio amp stage has serious shortcomings.
Regards, Mike VP8NO ----- Original Message ----- From: "Jim Brown" <[EMAIL PROTECTED]> To: "Elecraft List" <elecraft@mailman.qth.net> Sent: Monday, September 01, 2008 11:45 PM Subject: Re: [Elecraft] K3 Harmonic Distortion | On Mon, 01 Sep 2008 18:45:36 -0400, Jack Smith wrote: | | >I've found that the LIN OUT port has typical third harmonic levels | >around -45 dB from the fundamental, with the LIN OUT level set at 10, | >the factory default. The headphone port, under the same conditions, | will | >show the third harmonic down about 70 dB or so at levels appropriate | for | >my Sony high sensitivity headphones. Cranking the audio level up will | >cause higher distortion on the headphone port, but only at levels that | >are impossible to listen to as they are so loud as to be unbearable. | | >I've also seen some non-harmonic artifacts, particularly when very | >strong signals are pumped into the K3's antenna port. | | Jack, | | I assembled the first of the following reports in June after getting my | first K3 running, and sent privately to the guys at Elecraft. That's why | the new default LIN OUT gain is 10 rather than 50. It's also why there's | a note in the new manual about LIN OUT level. | | http://audiosystemsgroup.com/K3FilterStudy.pdf | | A month or two later, I prepared a report on filters in my Yaesu | FT1000MPs (mostly Inrads) and my K3. | | http://audiosystemsgroup.com/FilterTestNotes.pdf | | This second report describes the test methodology use for the earlier | work, which uses rather a high quality pro audio FFT system (EASERA | SysTun). | | My measurements compare pretty well with yours, but use a very different | measurement method that is not dependent on the distortion of a signal | generator. My method also makes the IM stick out like a sore thumb! | | As you can see from the first graph in the first pdf, distortion at the | headphone output (the black curve) is 0.02% 2nd harmonic, 0.014% 3rd | harmonic, and IM on the order of 0.1%. This was done at about 1 VRMS, | and was done after the LIN OUT measurements without changing levels. | | The only difference between Joe's measurements and mine is that my | analyzer has a bit more resolution, but we're all getting the same | result. The headphone out is VERY VERY VERY good, but the LiN Out starts | producing distortion at a rather low level. BUT, that low level is quite | sufficient to drive a sound card. | | As to the setting of 3 or 10. The distortion is mainly caused by the | output transformer, and distortion in an output transformer increases | rapidly at low frequencies when it approaches its amplitude limit. The | data output is MOSTLY intended for decoding digital signals, especially | RTTY, and the distortion at 2 kHz is a LOT less than at 400 Hz for the | same levels. But distortion is excited not only from signal, but from | noise, and impulse noise can get pretty high. | | Taking all of this into account, I run my LIN OUT gain at 3, and | recommend that setting. | | 73, | | Jim K9YC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
