D104 Question

[Glen Zook]

Although my Heath SB equipment will work fine without
the amplifier, I have found that by using it that I
can keep down the microphone gain (usually run it at
about 9:00 o'clock with the preamplifier) which
results in much lower hum and noise on the transmitted
audio.  On my SB-110A this is well over 30 dB less
hum!

The hum certainly meets specifications without the
preamplifier in use.  But, for example, when I am
working a local about a mile away my hum level runs
about S-8 when I am not using the preamplifier.  Of
course I am a true "60 dB over S-9" on my peaks.  When
I reduce the gain and then use the preamplifier, he
can just hear the hum and I am still "60 dB over S-9"!
 Of course, stations over 3 or 4 miles away cannot
hear the hum no matter which way I run the microphone.

My Collins S-Lines, on the other hand, seem to have a
lot more gain in the audio chain and are definitely
over driven by the D-104 with the preamplifier.

My Heath Apache and DX-100 work fine either way and my
Hammarlund HX-50A likes the microphone with the
preamplifier a bit better but will work fine without
it in use.

Most problems are due to the fact that the microphone
gain on the transmitter is not reduced by many
operators to compensate for the gain in the
preamplifier.  Thus, the audio circuits in the
transmitter are overdriven and definitely distort.
Also, like in my Collins S-Lines, in many rigs there
is already so much gain available that using the
microphone with the preamplifier engaged is just
asking for trouble!

That is why I rewired my D-104 with a switch that
allows me to engage the preamplifier when the rig
works better with it.  I have a switching box set up
so that I can use the same microphone on a number of
different rigs.  Not only do I switch the microphone,
but I also switch the push-to-talk function on the
microphone and on a foot pedal as well.

Glen, K9STH


--- EDWIN J FORWOOD <e.j.forwood at juno.com> wrote:

While it is true that some equipment may have some
additional gain when using the amplifier in the base
of the D104, I have found that none of my Heath SSB
equipment really need it.  The usual result is that a
lot of people ruin their audio output due to over
driving when using the amplifier.

=====
Glen, K9STH

Web sites

http://home.attbi.com/~k9sth
http://home.attbi.com/~zcomco

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