Clearly I must be missing something. In my view, all the reported distortion numbers are beyond expectations. After all you are buying a $2K radio, not a many kilobuck audio system.
The "problems" people are having with "harmonics" when they listen to CW with a 2.7KHz filter/DSP setting seem to be easily solved by just reducing the DSP bandwidth. The last resort solution is to get a few years older and you won't hear them. Workarounds for other problems seem to given in the postings. I personally hear and see nothing objectional given the above perspective. 73 de Brian/K3KO Joe Subich, W4TV-3 wrote: > > > VP8NO writes: > >> Perhaps someone suitably qualified and tooled up might like to try and >> [repeat] and comment upon the view presented by Rob Sherwood at the >> Dayton convention. According to him the K3 audio amp stage has >> serious shortcomings. > > I had to listen to the audio of Sherwood's talk before looking > in the right area. First, Rob doesn't say the K3 audio has > serious shortcomings, he complains about distortion on the > speaker. Sherwood also admits that using a high impedance > speaker (e.g., amplified computer speakers) or high impedance > headphones resolves the issue! > > My measurements did not show that distortion but I was measuring > at the headphone output with a high impedance load - the lowest > impedance headphones I use are 32 Ohms. As Jack Smith points > out, the headphones and the speakers have separate audio > amplifiers but share a common DAC. > > Since Sherwood's comments were based on the speaker output and > a LOW impedance load, I dragged out an old Optimus XTX25 speaker > - an unpowered 8 Ohm speaker I've used with other radios for many > years. With the 8 Ohm speaker is was easy to generate harmonic > distortion - particularly if the K3 were set to SPKRS = 2 with > only one speaker connected - simply by turning up the volume > until the amplifier was forced into clipping/saturation! > > With the 8 Ohm speaker, 1 to 2V peak represents a comfortable > to loud listening level for me. At those levels, the harmonics > are all down more than 65 dB and any other distortion is very > acceptable. > > The following table shows harmonic levels relative to a 500 Hz > reference tone at the given voltage across the speaker. 0 dB > is 1V Peak (.707V RMS). +10 dB represents 2.25V RMS (signal + > distortion). +13 dB is 3.2V RMS (the speaker amplifier is in > the compression region at the threshold of clipping) and +15 > dB is 4V RMS (the speaker amplifier is in hard clipping). > > Reference 2nd 3rd 4th 5th 6th 7th 8th 9th > ============================================================ > +15 dB -37 -15 -45 -26 -60 -43 -51 -37 > +13 dB -49 -31 -51 -35 -57 -39 -63 -49 > +10 dB -70 -68 -95 -67 -85 -69 -85 -73 > 0 dB -66 -74 -70 -77 -73 -76 -77 -80 > -10 dB -54 -66 -63 -90 -73 -82 -80 -87 > -20 dB -50 -78 -68 -74 -73 -74 -74 -78 > > In order to drive the audio amplifier hard enough to create > the distortion, it was necessary to disable the AGC or set > AGC SLP to low values (reduce the AGC reduction for strong > signals). > > Again, as in the case of the Line Out, if the audio gain, > AGC and RF gain are operated to keep the speaker amplifier > out of the clipping range - or away from the compression > region just before clipping - the distortion products are > entirely acceptable. For those with noisy shacks, impaired > hearing or using the internal speaker it may be difficult > to find a comfortable listening level without entering the > compression region. > > For those who wish to operate without AGC and with maximum > RF gain, I would suggest setting the AF gain to a moderate > level and using powered (computer) speakers or a 100 watt > per channel stereo amplifier capable of outputs greater > than the 1 watt per channel at .1% THD+N specified for the > LM4950 with an 8 Ohm load! Note, simply going from 8 to > 16 Ohm speakers will improve THD by 8 dB. > > 73, > > ... Joe, W4TV > > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > > -- View this message in context: http://n2.nabble.com/K3-Harmonic-Distortion-tp797780p836355.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: [email protected] 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
