[AMRadio] Microphone recomendation


Todd, KA1KAQ ka1kaq at gmail.com
Mon Sep 21 15:24:31 EDT 2009


On Mon, Sep 21, 2009 at 11:09 AM, Gerald Stockinger <
cliogunsmith at centurytel.net> wrote:

>
> Good morning to all. Since I will soon be new to AM having been on SSB
> since 1957 I need the benefit of others experience. Last week a good
> amount of time was spent on audio quality so I thought I would ask here.
> The rig is a Collins KW-1. I need a good quality (broadcast if you will)
> microphone to use with it, I have a deep voice and I sound terrible on a
> 300 to 3000 mic. I need more lows than  that. I welcome any suggestions
> on what microphone might fill my needs.
>

Welcome to the KW-1 club, Jerry. I've had mine since 1988, pretty sure it
was my first AM transmitter on the air too, otherwise the 32V gets the
honor.

Rob brings up a good point: where your transmitter fell in the production
(first or last half, basically) will determine how it will sound with any
mic. Later production units had tighter audio and require a fattening of the
coupling caps along with a few other tweaks to get better audio. Later
models had better plate blocking and a few other perks though, so it all
evens out.

Required reading IMO if you don't already have it is Electric Radio #23,
March 1991. It's a special edition entirely about the KW-1 with stories from
then-current owners as well as an article by Jay Bromley W5JAY (then KA5DGH)
on making audio improvements to the transmitter. I did most of these mods
from a sheet sent to me by Uncle Ed, WA3PUN who is a former owner.
Basically, bypass the clipper and splatter choke, fatten up the coupling
caps from .01s to .1s, and change the grid resistor in the 12AXY mic input
circuit from the stock 1 meg to 4+ megs (Jay suggests 5M or more, but I used
4.7 and it sounds good). I didn't replace the 872s with SS sticks, but
instead used 4B32s which are a drop in sub that you can find with the same
glass envelope as the 872s if aesthetics are important.

I've always used a crystal D-104 with excellent results, both on the KW-1
and 32V. These mods are pretty much tailored to that impedence. Another good
ER issue to read on this matter is October '93 #54 I think. Gary Halverson
gives an excellent explanation of mics, audio, and what's involved.
Personally, I've never heard a Heil mic I liked, but I haven't heard the
newer ones and it's just my opinion. As soon as you start adding processing
to change characteristics, it all goes out the window IMO. Gary's article is
good for this info, such as having to equalize and boost the ribbon mics and
such. Nothing against processing, but if you do the simple mods to the audio
of your transmitter and plug in a decent D-104 (make sure the element is in
good shape with a scope), you'll be very pleased.

If you want to go the processed sound route, simple feed it into the phone
patch jack (you'll still have to do the other mods) and you're good to go.
You can probably make a soup can sound decent with enough processing, so mic
choice becomes more a choice of preference and less one of performance.

~ Todd,  KA1KAQ/4.


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