[AMRadio] Mike

Bob Bruhns bbruhns at erols.com
Tue Mar 15 23:22:16 EST 2005

> Personally, my voice is a little higher from center in pitch..and I'd
> prefer more lower than higher freq. response...which is generally
> a problem due to low freq. rolloff in the mike curves...

Steve, this makes me think that your best bet would be to close-talk a
unidirectional mike.  A low-cost ball-head dynamic unidirectional stage mike
would probably be your best bet.  The "proximity effect" of these
microphones give a voice much more depth, and for some reason it is really
rare for this effect to be duplicated well by electronic frequency response
equalization.  If you can find an old Shure SM58... Of course, that's a
"low-Z" dynamic mike, so you would want a matching transformer to give the
grids more signal level.  Some of these microphones have a "high Z" output,
though, which is what you want with a tube audio chain.  But one problem
with dynamic mikes in ham stations is magnetic hum pickup.  So you might do
well with a low cost unidirectional condenser mike.  For some reason, these
mikes usually sound muddy and require more midrange and high boost, though.

3 KHz boost is still a good thing, too.  With the bass boost you'll get from
proximity effect, you'll probably want a lot of 3 KHz boost.  As long as you
have enough deep low end, this kind of high-boosting does not make your
voice sound higher pitched, it makes it sound clearer.  And this frequency
range is usually best equalized with electronics.  There are a number of
ways to do it.  One simple trick is to remove two or three cathode bypass
capacitors in the low level audio chain and put in relatively small
capacitor values. Divide 210 by the cathode resistor value and use about
that many uF of cathode bypass capacitance.  So with a 1K cathode resistor,
use a 0.22 uF bypass cap.  The bypass effect works strongly at higher audio
frequencies, but only weakly at lower frequencies, so the effect is a high
frequncy boost.  However, this boost comes at the cost of gain that you
would otherwise have had in the middle and low frequency range.

If you get into resonator design, you could take a 2 or 4 KHz peaker from a
graphic equalizer, and move it to 3 KHz, and experiment with the Q of the
resonance.  You want a fairly low Q (broad) peak at about 3 KHz or just a
little lower (like 2.9KHz).

  Bacon, WA3WDR

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