[Kenwood] TS-940 Audio Problem

[ad6zu at comcast.net]

It sounds like RF is getting into the microphone.  The MC60 is pretty notorious for that.  Try these:

1. Turn the mike amplification off.  You never needed it with the TS940 anyway.  That's what the mike gain control is for.

2. Disconnect the microphone from the base and plug it into the 940 directly.  For me, that fixed the problem.  
I also noticed I got a good jolt when using a D-104 with the all-chrome body.  That gave me another clue that I had a bunch of RF in the shack :)

3. Transmit into a dummy load and listen in on a nearby rig.  Let's you know that RF IS getting into the mike.

Once I tried the mike without the base, I proceded to do the MC60 mike base fix.  I performed the fix that uses a couple of capacitors.  I think it was in mods.dk before it became a pay site.

Roy 
AD6ZU

----- Original Message -----
From: Dennis Klipa 
To: kenwood at mailman.qth.net
Sent: Tue, 3 Nov 2009 00:34:28 +0000 (UTC)
Subject: [Kenwood] TS-940 Audio Problem


When my friend, John, transmits on LSB on his TS-940 with his MC-60 microphone, it sounds like all of the bass has been stripped from his voice, as if there were a narrow band filter in the mic circuit. This is true on all bands.  We have taken his microphone and put in on my TS-940 and it sounds great, according to on air reports.  It is a little more sensitive that my MC-60 but we only have to turn down the mic gain one notch to keep the ALC within range with his mic on my 940.  It doesn't matter which impedance you select on the mic or whether the preamp in the mic base is on
or off, the audio still sounds bad.   The speech processor is turn off.  Turning it on only makes matters worse.  So it is not the microphone.

When we turn down the Power down on his rig to about 5 watts out, the audio quality increases but only slightly.
We have tried LSB, USB, AM and FM modes.   The problem is only present on LSB.
The obvious adjustments to check are:
1.  SSB Mode Frequency Response
2. Supply Voltages
3. Carrier Suppression (balanced)
 
But before I open the cover, I wanted to find out if anyone had experienced
this problem before or has any suggestions on what to look for.


Thanks, es 73,
Dennis, N8ERF