[Elecraft] Mics

[Jim Brown]

On Mon, 5 Jan 2004 08:24:16 -0700, Augie Hansen wrote:

>Being a long-time Icom user before (and since) building K2 #3302 I have
>plenty of experience with rigs that need to be driven with higher level
>audio. 

While I strongly agree that Heil mics are wildly overpriced and over
valued, the heart of the problem is the absence of a real STANDARD for
what the output voltage and impedance of a microphone used in ham gear
ought to be, as well as poor frequency response shaping in many modern
rigs. There is something seriously wrong with the design of ham gear
when a good pro mic with flat response sounds muddy and bassy on the
air. FWIW, this is NOT the case with the K2 input stage, which, once
you give it enough gain, sounds quite good with a flat pro mic. 

For at least 40 years, 150-250 ohms has been standard for professional
low impedance microphones, both dynamic and electret, but their voltage
sensitivities vary over a range of 10-20 dB.  For some strange reason,
the ham manufacturers seem to have gravitated to 500 ohms. This
impedance difference alone will account for 6 dB of gain required at an
input stage. And some mics have built-in preamps, some don't. The
impedance difference, and the wide range of mic output levels, combine
to make it more expensive to design an input stage to accommodate what
looks like a reasonable selection of mics but really isn't all that
reasonable.  

Engineering is all about cost effective design, and Elecraft has done a
magnificent job of giving us a huge bang for our buck. But one of the
consequences of any set of design compromises is that there are limits
on what will work with what. In the K2, the only gain control consists
of a 180 ohm resistor that can be switched in and out of the circuit to
accommodate a hot mic or a noisy location. That's a cost compromise,
but it saves a pot (and the space for it), a gain stage, and the means
to control it.  Ya pays yer money and ya takes yer choice. 

Jim K9YC