[Icom] 756PROII hum on external audio

Wed, 28 May 2003 12:03:34 -0400

Is the external speaker powered in any way, i.e., amplified or containing
DSP or other active circuitry? If so, you could be experiencing a "ground
loop". Try disconnecting the sleeve connection at the speaker's input
connector (the audio will still get a return path if a ground loop exists,
usually through the 12 volt power connection). The idea is to break the
loop, so that there is only one path for the audio return line.

Another possibility is electromagnetic pickup of the circuitry inside the
speaker. Relay or solenoid coils that are energizing when you activate
certain controls on the rotator controller may be inducing 60Hz hum into
sensitive stages inside an active speaker, or in extreme cases, could even
directly couple to the voice coil in the driver itself. Physical separation
is the cure in that instance.

I hope this helps.

William J. Wickstrom
Chief Engineer
Surge Performance Sound
[email protected]

William J. Wickstrom, W1IK/NNN0AHC
President, Morse Instruction Coordinator
Utica/Shelby Emergency Communications Association (USECA)
[email protected]; [email protected]
www.useca.net

From: "TLW" <[email protected]>
To: <[email protected]>
Date: Tue, 27 May 2003 21:52:38 -0400
Subject: [Icom] 756PROII hum on external audio
Reply-To: [email protected]

I'm having hum on the external spkr jack when I pull the brake on the
antenna rotor; the control box is about 4" above the rig. Has anyone
else seen such a problem or know how to fix it? The internal spkr and
headphones to front jack are clean: the external spkr or headphones to
jack on ext. spkr have humm w/brake pulled.
Terry Wells