This subject doesn't have to be difficult.
A couple years ago using my Omni V and testing with 4 individuals on the air
that know my voice in person. I compared a non-amplified and an amplified
D104 against the 705, the TT hand mic (took second place by the way), a
Heil/5, and a 444 dual impedance (yes, it sounds good). The D104 sounded the
most natural and I wound up using a non-amplified D104 for about 2 years
before using what I use today (I won't go into that). My voice is not
squeaky and not ultra bassy.
Try a D104 with someone you trust on evaluating how you sound. If it sounds
good, use it! If it doesn't sound good, modify it. If you aren't capable of
modifying it, sit it on the shelf, make a lamp out of it, throw it in the
trash, or sell it! Go out and get another mic and try again!
J/KM6VX
-----Original Message-----
From: Paul Christensen [mailto:paulc@mediaone.net]
Sent: Monday, March 20, 2000 11:19 AM
To: Tentec Users Reflector; John Vickers
Subject: Re: [TenTec] d-104 and omni V
The secret to making the D-104's high-impedance crystal mic element sound
great rests in adequate buffering between the crystal element and the
relatively low input impedance of the transmitter.
Think of the crystal element as a network consisting of a voltage generator
in *series* with a small value capacitor. The more this simple two element
circuit is loaded at the transmitter, the more low-end roll off occurs.
Typical values of the source capacitance for the crystal microphone element
are from 800-1200 pF. Now, calculate the -3dB point using the reciprocal of
2*Pi*RC. Assuming a source capacitance of 1200pF and a high input impedance
(e.g., 1 MegOhm) of the transmitter, the -3dB turnover point is 132 Hz!
With 100K of loading it worsens to 1.3 kHz! No wonder why a straight D-104
sounds so "tinny" on modern transceivers.
At one time, Astatic offered the D-104 without a two-transistor preamp for
use with grid-driven vacuum tube speech amps. Because of the very high
input impedance of the tube's grid, the D-104 can sound wonderful on a tube
transmitter. Later, Astatic employed the two-transistor "preamp" as a
buffer for the crystal element, not to be meant as a true preamp.
Nevertheless, Astatic's buffer still presents a load far too low for the
crystal element. A much better and simplistic method involves the use of a
single MPF-102 FET transistor configured as a source follower. The input
impedance is 11 MegOhm, the voltage gain is slightly less than 1.0, and the
output impedance is is determined by a single resistor from the FET's Drain
to ground. I typically use 330 ohms for use with a high or low input
transceiver. Now, my D-104s sound every bit as good as any dynamic mic.
The cost of the circuit mod is less than $3.00 and it can be installed in
place of Astatic's 2 transistor preamp. Also, it will sound every bit as
good as that $125.00 mod that is available on the Internet. Hmmm, I wonder
what circuit they're using in theirs!
-Paul, W9AC
-----Original Message-----
From: John Vickers <wa4tt@nlamerica.com>
To: Tentec Users Reflector <tentec@contesting.com>
To: <tentec@contesting.com>
Date: Monday, March 20, 2000 1:29 PM
Subject: Re: [TenTec] d-104 and omni V
>
>Carl S. Hyde W2CSH Wrote:
>
>
>>
>>The D-104 mics are made for CB radios. They have a low
>>frequency roll-off from about 1 KHz on down. They also
>>boost higher frequencies. In other words they suck!!!
>>But if you insist on using one there is a company that
>>for $125.00 will make a D-104 sound like a real ham
>>radio microphone.
>
>
>Hi Carl es all--- The D104 was in use BEFORE the 11 Meter CB band was even
>established. The CBers starterd using theD104 because it made their
>stations look more like ham rigs. Then the Mfg started targeting that
market
>with its Golden Eagles, silver Eagles, Black Crows, Dead Ducks, Etc, Etc.
>
>In the hands of someone with a basic knowledge of radio the 104 can be made
>to work just fine on the Ten Tec rigs. Some of the guys with higher
pitched
>voices need to loosen their shorts or try another brand of mic. BUT PLEASE
>don't pay $125 to some outfit to do to your mic -- what any true ham should
>be able to do for himself.
>73 John WA4TT
>
>--
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