On 9/5/2017 1:21 PM, Joe Subich, W4TV wrote:
You will find almost without fail, the common emitter transistor preamp with unbypassed emitter bias resistor is, in fact, clipping well below 1V.
Gee, I said 100 mV, which is 20 dB below 1 V.
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
I am well aware of the differences -- that was my profession for 50 years, and, among other things, I'm still on the AES Standards Committee, which standardizes stuff like this! Indeed, consumer line inputs (into which ham gear falls) typically clip around 1V. Nowadays, pro line level equipment clips in the range of +18 to +24 dBu. That's a lot more than 4V P-P.
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.
I suggest that you drag out a scope and look at the output of some these mics with speech with different people and different working distances. The variables are distance and how loud the speech is. I know guys who get pretty excited calling DX or during a contest. And sound pressure level follows inverse square law, just like antennas. That means the voltage doubles (+6dB) every time the distance between mic and mouth drops by a factor of 2. 1-in to 2-in is 6 dB. 2-in to 4-in is 6 dB. 4-in to 8-in is 6 dB. And having ridden gain on a wide variety of performers for 50 years, I can assure you that it is VERY common for speech levels to vary by 20 dB in perfectly ordinary speech.
All of this information is available from public sources and a little study.
I learned it more than 50 years ago. :) 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]
