Great Sounding Homebrew Microphone For About 5 Bucks
When I built my AM transmitter I
looked around for a nice broadcast quality microphone to use with it.
After gasping at the prices, I decided to see what I could come up with
for less (much less) money. I grabbed one of the cheap 2 lead PC
condenser elements at a local Radio Shack and found that they actually
sounded pretty decent. The biggest drawback was that they seemed to
have a very boomy low end that made them difficult to work with. The
solution to that was to use a pre-emphasis RC network similar to what
is used in many FM transmitters to produce a flatter response and more
vocal presence. The end result is what I have been using with most of
my transmitters ever since. I get lots of unsolicited comments about
the smooth and natural sounding audio, and lots of laughs when I tell
people what I'm using. If you are looking for a cheap way to improve
your audio, go spend 5 bucks and give it a try. You can tell people
it's a Heil PR780 with a Symetrix 528E if you want. They'll
probably believe you.
The circuit above is mounted in an old Peavey microphone case.
Not quite in focus but I really like the score in the background.
The circuit above is mounted in an old Peavey microphone case.
Not quite in focus but I really like the score in the background.
Back in 1989 someone recorded my
signal on 75 meters while I was using the 5 dollar microphone with my 4-400 AM
rig.
The sound clip ended up in the AM audio vault at the
AMfone web site. I
never found out who made the recording, but they had a terrific receive
setup. Listen for yourself and see how the 5 dollar project sounds to
your ears. (Note: At the time, my callsign was WB1AEX.)
75 Meter AM QSO from
1989 (0.38
meg mp3 file)
During the summer of 2009 I resurrected one of my
AM rigs and once again relied upon the same
electret element microphone design. I get excellent reports with this
setup in spite of the small investment in the audio system. The
microphone is run directly into my computer soundcard where the audio
is processed
with free software called Voice Shaper. The audio output of the
soundcard is then run through a JBL 7110 compressor
limiter to a solid state amplifer that drives the grids of a pair of
811A tubes. This audio clip was recorded by Eric WB2CAU with his Flex
SDR station.
75
Meter AM QSO from 2009 (0.36 meg mp3 file)The SSB audio clip below was made
by Eric -
WB2CAU on 75 meters in the fall of 2008. He has a very nice
SDR station which is capable of making high quality
recordings. The microphone is the very same 5 dollar
microphone
that I put together back in the early 80's. Eric informed me that I was
a few cycles off frequency when
he made the recording, but you can still get an idea of how the
microphone performs on sideband as I'm babbling away. The transmitter
used is a 756 Pro
III
in the 2.9 kc bandwidth position and the microphone is patched right
into the front panel mic jack.
75 Meter SSB QSO (0.89
meg mp3 file)
Transmit audio in ham radio is
entirely subjective, but spending less than 5 bucks for a microphone is
priceless! There is a fair amount of tonal adjustment available with
the 10k variable resistor, so it is very simple to make the microphone
sound very different to suit your taste. Using a .01uf capacitor
instead of the .05uf will also have a big effect on the frequency
response as well. It's worth playing with to find what suits your own
voice. Good luck!
Radio Shack Parts List:
10K-Ohm 15-Turn Cermet Potentiometer/Trimmer Model: 271-343 | Catalog #: 271-343 $2.69
PC-Mount condenser Microphone Element Model: 270-090 | Catalog #: 270-090 $2.79
0.047µF 50V 10% PC-Mount Capacitor Model: 272-1068 | Catalog #: 272-1068 $1.49
Radio Shack Parts List:
10K-Ohm 15-Turn Cermet Potentiometer/Trimmer Model: 271-343 | Catalog #: 271-343 $2.69
PC-Mount condenser Microphone Element Model: 270-090 | Catalog #: 270-090 $2.79
0.047µF 50V 10% PC-Mount Capacitor Model: 272-1068 | Catalog #: 272-1068 $1.49