nuckolls.bob(at)aeroelect
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 Posted: Mon Dec 02, 2013 2:06 pm Post subject: Two Audios wired to One PM-3000 input thru a 500ohm resist |
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At 03:00 PM 12/2/2013, you wrote:
Hi,
I am installing a PM-3000, 11931-A in my SeaRey Amphibian. This
device has two Un-switched inputs, and I have three audio output
warning devices. I have gained some understanding from the archives
that an isolation amplifier is needed to make this work properly, but
the SeaRey factory and dealer are telling me that all I need to do is
to connect my Gear Alert and my Power Buss alert audio wires to a
500ohm resistor each, and connect them to a single un-switched audio
input on the PM-3000. Both of these devices have adjustable gain. The
remaining input connects to the SkyView audio out.
The instruction is qualified with the fact that this has been
performed satisfactorily on many of these aircraft. Yet what I
learned from The List, and from AE Connection, leaves me skeptical.
I sent a note to PS Engineering over a week ago, no response yet.
The two-resistor-mixer technique will work. You
may find it useful/necessary to fiddle the
the resistor sizes to get the volume you want
from each tone. Increasing the size of the resistor
decreases volume. When trying a different size
resistor, make about a 20% jump from the previous
value. 500 or even 510 are not real common. Start
with 470 ohms, 1/2w.
Can anyone shed some light on how acceptable this is, or why and how
I should do something different?
I also am a little troubled by the SkyView instructions for multiple
SV Screens, that CLEARLY state; to electrically connect both left and
right stereo outputs together at each screen connector (creating a
Mono output), PLUS to jumper across all screens. This is to ensure
that regardless of power to any screen, all audio warning will be
heard. This is not only clearly communicated, they provide an example
making clear all 4 audio outputs of a two screen system are twisted
together and fed to one input on the Intercom. Any comments regarding
this instruction?
Hmmmm . . . are these warnings FROM the SkyView
instruments . . . and they are stereo?
You might go the resistor-mixer route here
too starting with 470 ohms in each of the feeds
brought together the OTHER un-switched input to
the PM3000.
If push comes to shove, you can craft an
isolation amp from our DIY plans and ecb
or exploit a number of manufactured options.a
Bob . . .
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