Hi Brian, I've run THD (on the analog signals) and IMD (on the RF signals). What I hear correlates strongly with IMD levels at lower powers (where much of our voice energy is) when compared between 5K driver, 5K final, and a 1k. Correlation does not mean causality, but...no one has yet come up with a better idea.
Other notes... I recalibrated the bias and power (default bias seems to be 1.0A for the drivers and 2.0A for the finals). I can't tell if there's a change in distortion or not, but IMD did not change appreciably (a dB or so). Will listen again tomorrow - my ears are tired. Also, I tried 10-band EQ settings from Dale. No joy. Does anyone who is familiar with the 5K circuitry (and understands PA design - this isn't my field) have any ideas for improving the linearity of the PA final stage? (Apart from adjusting bias, that is.) This would be a great experiment to try. - Jeff Brian Lloyd wrote: > On Jul 8, 2008, at 12:18 PM, K6JEK wrote: > > >> It not just Jeff. I'm one of the guys who've been listening to the >> various audio tests. We first noticed something funny in someone >> else's 5000 before Jeff even got his. We ran experiment after >> experiment. This guy finally returned his for a refund. Then another >> fellow (not in the local rag chew group) broke in with his 5000 to >> say he's just waiting for someone to figure this out. His 5000 had >> the same problem. We've been listening and recording with a variety >> of equipment ranging from 1000's to direct conversion home brews. >> >> It is subtle. It might be rare. But it is not unique to JCA >> >> I think Jeff's nailed it. The audio up through the driver stage is >> perfect. It gets funky in the final. Why and what to do about it is >> another matter. >> > > Has anyone run single-tone and two-tone tests and looked at the > distortion products? (THD and IMD). If you can hear it you can > probably measure it. The spectrum will tell you something about what > might be causing it. > > Oh, has anyone looked at the gain of the PA? If the PA uses feedback > to linearize it, there may be a problem with the feedback loop and the > PA may be running open-loop. > > -- > > 73 de Brian, WB6RQN > Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com > > > > > _______________________________________________ > FlexRadio Systems Mailing List > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > Knowledge Base: http://kb.flex-radio.com/ Homepage: > http://www.flex-radio.com/ > > > _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
