The audio ADC used in the KX3 has a recommended "Analog full-scale 0-dB input voltage” of 0.63 VRMS.
I’ll let someone else go through the K3/K3S schematics. wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Sep 5, 2017, at 1:21 PM, Joe Subich, W4TV <[email protected]> wrote: > > > Jim, > > Get some real world experience with typical amateur transceivers. > Dig out the service manuals and run their mic circuits through SPICE > or one of the other software programs that will show you where they > clip. You will find almost without fail, the common emitter transistor > preamp with unbypassed emitter bias resistor is, in fact, clipping well > below 1V. Those preamps invariably have between 26 and 30 dB of gain > and the outputs are connected in parallel (with or without switching) with > the "Line In" (old Patch jack which was typically rated for 100 - > 500 mV) which then drove the audio stage which included the mic gain > control. > > Remember, we're talking about *AMATEUR* equipment - not professional > and broadcast equipment with its 1V or 4V P-P standard "Line" levels > and wide range mic preamps that provided standard level outputs > > Some newer rigs do better - high impedance, low noise op amp preamps > that are much less sensitive to overload. TenTec had a "line" input > with a 4V P-P tolerance but those "features" are far from the norm, > particularly considering the number of 25 and 30 year old rigs still > on the air. > > In any case, a typical dynamic microphone - professional or amateur - > is rated around -55 dBV/Pascal (check Shure, EV, etc.) some may be a > more sensitive, some less. For those who do not know, 1 Pascal is a > 94 dB Sound Pressure Level (think traffic on a busy roadway) - nearly > 25 dB above the EPA threshold for hearing protection! -55dBV is in > *the millivolt range*. 5 mV is a decent level for normal conversation > with a dynamic microphone within 6" of the lips. > > All of this information is available from public sources and a little > study. > > 73, > > ... Joe, W4TV > > > On 9/5/2017 1:17 PM, Jim Brown wrote: >> On 9/5/2017 6:24 AM, Joe Subich, W4TV wrote: >>> >>> A transceiver designed for use with a dynamic mic (Kenwood, TenTec, >>> Kenwood, etc.) typically expects 5 mV (or less) on the mic input. The >>> attenuation needed to reduce 1 V to 50 mV is 46 dB (20log(.005/1)). >> Joe, >> While I greatly respect your engineering, the output of a dynamic mic varies >> widely depending on what it's hearing. The classic "little old lady on a >> lavalier" in a TV studio may produce only 5-10mV, but when worked close to >> the mouth, as most ham mics should be used, the output is more like 100 mV. >> The fictional lead vocalist Arthur Leatherlungs can easily drive a dynamic >> mic to 1 V. Not only that, many ham mics are electrets, which tend to have >> output levels equal to or greater than dynamic mics. The mic input stage >> must accommodate all of these mics. Although I've not measured input clip >> levels of ham gear, I'd be quite surprised if they clipped below about 100 >> mV. And clip level is what matters. >> As to computer output levels -- while RATED output level for clip is >> typically in the range of 1V RMS, some I've measured suffer from increasing >> distortion 6 dB below their actual clip level. I've measured -30 dB >> harmonics just below clip, and -40dB at 6 dB below maximum output. Further, >> while pro systems are correctly adjusted so that all stages in a signal >> chain clip at the same level to maximize signal to noise, those systems are >> going for 100 dB or better. Few ham systems need better than 50 dB SNR in >> the audio spectrum, but distortion products can be critical. SO -- the >> output of a computer audio interface should not be run at its maximum level, >> certainly not hotter than about 0.5V RMS. >> Years ago, the venerable Shure M67 and M68 were designed so that they >> clipped in the range of 50 mV, and Shure had to sell inline pads (10-15 dB >> attenuators) to prevent overload. A new company, Tapco, led by Greg Mackie >> developed new inexpensive small mixers to compete with Shure, and ended up >> eating Shure's lunch with an input circuit with feedback control of input >> gain that handled much higher signals without overload. For at least 40 >> years, any pro mic input will handle signals up to at least 3V RMS through >> the combined use of switchable pads and feedback gain control. >> 73, Jim K9YC >> ______________________________________________________________ >> 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 >> Message delivered to [email protected] > ______________________________________________________________ > 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 > Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
