[TenTec] Omni 6 Plus Distorted Audio

Thu Jun 20 20:37:16 EDT 2013

There is a CW wave shape adjustment on the bottom side.  That might be 
adjusted incorrectly.  It really takes a scope to do this but it seems you 
have the knowledge and equipment to do so.

As to the RF distorted audio, sounds like  RF into the audio.  Works OK at 
low levels but distorted at 100 watts.  I seem to recall that the Heil mod 
adds gain to the mike circuit. This make it more susceptible for RF in the 
audio issues.

This Aux audio input is really just another input to the mike audio circuit. 
Don't try to use both at the same time.  Only use/connect one input at a 
time.   Also, attenuate the level at the radio and not at the soundcard end 
so the level on the cable is as high as possible.  Then attenuate at the 
radio.  I've found this method to work better.

Be sure there is a hard ground between the radio and the power supply 
ground. Do not rely on the DC power cable and connectors for ground between 
the radio and power supply.   Also check to see that the ground terminal at 
the radio, specifically inside is tight.  The DC connector negative is 
connected to this terminal inside the radio.

Be sure the Speech Processor is OFF.

I might have more notes in my service manual, but for now, this is all I can 
think of.

73
Bob, K4TAX

----- Original Message ----- 
From: "Mike" <mike at n1mb.com>
To: <tentec at contesting.com>
Sent: Thursday, June 20, 2013 12:23 PM
Subject: [TenTec] Omni 6 Plus Distorted Audio

> Hello Everyone,
> I researched all of the threads before posting. I recently purchased an 
> Omni VI Plus that has the SMT boards. It has the 2.8 Khz Inrad Filter as 
> well as ALL of the other filters for CW.
> When I got it there was severe chirp and key clicks. I spoke with TenTec 
> about this and they suggested that I look at the DC board which I did and 
> found connector 5 unplugged. I reattached this connector and 95% of the 
> chirp was gone as was the key clicks. I looked at the cw waveform before 
> and after and the difference was substantial.
> TenTec had worked on this unit a month before I bought it and gave it a 
> clean bill of health and indicated that there is a Heil mod on the TX 
> Audio board. I looked at the schematic for the 564 which indicates that 
> resistor R54 should be 47k and that R55 should be 100k. TenTec said the 
> Heil mod changes the resistors R54 to 22k and R54 470k. My unit has the 
> factory resistor values of 47k and 100k. So it really didn't have the Heil 
> mod after all. They recommended a 330 k for R55. If you look at the 563 
> model it has the 330k resistor but not the 564. So I wonder if there was a 
> reason for dropping the value of R55 from 330k to 100k between models?
>
> On the 9Mhz filter board there is a mod changing C37, C47 and removing the 
> 2.2M resistor. It looks like a suggested mod from W9AC. I changed these 
> values back to factory specs and the only thing that changes was the CW 
> waveform wasn't as nice as was with the mod, so I went back with the mod 
> components. I do not physically see other modifications to the unit.
>
> The signal coming out of connector 79 from the low level driver board 
> monitored on a second receiver and scope indicates clear undistorted 
> audio. However, when I reconnect to the finals everything is distorted. I 
> tried both methods of adjusting the bias, the one in the 564 manual and 
> then the VE1CHS method to no avail. The PA will produce full 100 watts of 
> power into a dummy load and the CW mode seems to be working fine with only 
> a faint hint of chirp when tuned to the 16th octave.
>
> Is there anyone familiar enough with this particular model that could shed 
> some light on the distorted audio given that I have the mic gain set to 
> just below where the ALC light flickers and have tried all power settings 
> and mic settings and a total of 3 different mics. I also connected it to 
> FLDIGI to see if I could work PSK31 with another ham a few miles away and 
> he could not decode. He further indicated that it looked like I was over 
> driving the audio. I placed a voltage divider of 100k inline and 10k  to 
> ground to the sound card audio and varied the audio with the sound card 
> control as well as the Omni 6 + audio gain control. It was still distorted 
> even when the output was all the way down to 5 watts.
>
> I would appreciate any information.
>
> Thanks,
>
> Mike
> N1MB
> ps I have owned several of these units and this is the only one that 
> exhibits this problem.
>
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