W3YY Audio Control System
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The purpose of the audio control
system was to provide a way to control the routing and levels of all transmit
and receive audio in the shack, through a convenient centralized control
point. I wanted a very high-quality audio system and one that was immune
to the RF that might be floating around the shack. The system I designed
and implemented has met these goals.
The audio control system at W3YY
is built around a very high-quality, but low-cost audio mixer, the Behringer
UB802. This 
mixer is an amazing value. I've been buying audio mixers
since the 1950's. Those early cheap mixers, that I could afford as a
teenager, were built around the CK722 transistor! That transistor was so
noisy I think the mixers had a S/N ratio of about 20dB! The UB802 costs
only around $60 today (probably about $6 in 1950 dollars), but has professional
specifications and performance. Balanced +4dBu I/O, phantom powering, XLR
microphone inputs, it's got almost everything you'd like, except for pre-fader
sends (I'll explain later).
The audio system provides the
following functions:
Main Receiver Audio
Sub-Receiver Audio
When I operate split I place
the main receiver audio (the DX station I'm listening to) in the center of the
sound stage and the sub-receiver audio over on the right. Levels are
adjusted so I can hear enough of the pileup to know what's happening, but not
enough to interfere with listening to the DX.
Microphone Audio
-
Adjust monitor level in the
headphones.
-
Pan monitored audio left and
right in the stereo sound field. (I typically have this over on the
left side.)
-
3-band frequency equalization.
-
Adjust audio level sent to the
transmitter.
PC-Generated Audio
-
Adjust monitor level in the
headphones.
-
Pan monitored audio left and
right in the stereo sound field. (I typically have this over on the
left side for Phone contesting.)
-
3-band frequency equalization.
-
Adjust audio level sent to the
transmitter.
Click on the link below to see a
block diagram of the system. You will note that isolation transformers are
used extensively to both eliminate ground loops and provide conversion between
unbalanced audio connections (the kind typically found on ham equipment and
consumer audio gear) and balanced audio connections (the kind typically found on
pro-audio equipment and the UB-802). I used EBTech Hum Eliminators, which
contain two high-quality isolation transformers each.
EBTech Hum Eliminator
(This page under construction -
more details, photos, etc. to follow.)
audio_system_w3yy.pdf - W3YY Audio Control System Diagram
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