[TenTec] Omni VI audio problem

Mon Sep 17 22:41:24 EDT 2018

Hi Bob,

I removed the split core I had on the audio cable and put a solid core 
with several turns of the the audio cable wrapped around the core at the 
sound card output.  That drastically reduced the hash picked up from the 
PC.  So, it should  have a MUCH cleaner digital signal now.  Now when I 
remove the mic and short pin 3 to ground and turn the mic gain fully 
clockwise, the rig is putting out maybe 1 watt. Much better than the 100 
watts it was putting out when I tried the same thing before!  Yeah, it 
is a bummer that both are hot all the time.   I'll have to remember to 
disconnect the cable from the PC when operating phone.  Would have been 
nice if one were able to select the audio source.

Thanks for your help.  Hopefully I'll sound better when I check into the 
net now :)

73

Stan
KM4HQE

On 9/17/2018 9:25 PM, Bob McGraw K4TAX wrote:
> Stan
> Unfortunately that input on the rear is "hot" all of the time and the signal (noise) is mixed with mike audio. It is isolated by a 10k ohm resistor.  The MIC gain and SP level controls both inputs.
>
> You must physically connect one or the other, but never both. There is no provision in the radio to select between the two inputs.
>
> I wouldn't bother with chokes as any noise from the computer or interface will appear in mike audio.   Just the way it works. Bummer.
>
>
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Sep 17, 2018, at 9:16 PM, Stan Gammons <s_gammons at charter.net> wrote:
>>
>> Hi Bob,
>>
>> One thing I forgot to check before and I pretty sure I found out what the problem is.  I have the PC soundcard out connected to the audio in on the back of the radio so I can use it for digital modes.  Seems as though it's picking up hash from the PC and it's getting mixed with the audio from the mic. When I disconnect the cable from the PC, things are normal.  Dang it!  Guess I need to put another or more ferrite cores on the audio cable.  I hear the computer hash when I test PTT with WSJT-X too.  So it's transmitting a cruddy digital signal too.  That's unacceptable.  I have to fix that.
>>
>>
>> 73
>>
>> Stan
>> KM4HQE
>>
>>> On 9/17/2018 8:51 PM, Bob McGraw K4TAX wrote:
>>> Stan:
>>>
>>> First I suggest turning the speech processor OFF and forever leave it OFF.    If you want to use it, just remember,  more is worse.
>>>
>>> Even though the mikes worked on the TR7, I view this is no indication the wiring is correct for the Omni VI.  I suggest checking the manual for the correct mike wiring and physically confirm the mike of choice is wired correctly.    I find mike wiring standards to be as varied as dust particles in a Texas sandstorm.
>>>
>>> Pin #1 is mike high or mike audio
>>>
>>> Pin #2 is ground and shield.  Be sure the shield of the mike cable also folds back into the Amphenol cable connector to make contact with the shell.
>>>
>>> Pin #3 is PTT
>>>
>>> Pin #4 is  +4 DCV for use with an Electrect mike.
>>>
>>> Check the plug in filters on the bottom to see they are seated correctly and correct location.  Again, contact cleaning of their pins might be in order.
>>>
>>> One other test, disconnect the mike, turn the MIC gain fully counterclockwise {off}, transmit and listen to the radio.  With the 2nd receiver, tune across the frequency and listen for carrier.  In general all should be quiet.  If you hear significant carrier, there is a procedure to null the carrier.  Probably need an oscilloscope and dummy load to do that.
>>>
>>> Next would be to check the frequency of the BFO crystals.  Again there is an alignment procedure.  This must be adjusted in the exact steps outlined in the manual as there is interaction between the adjustments.  Repeat the procedure a couple of times.   A frequency counter is required for this adjustment.  Don't skip one step just because you don't intend to use that mode.  There is interaction between the adjustments.
>>>
>>> And of course my last suggestion, which normally is my first suggestion..........take time to pull each cable, using a Q-Tip moistened with contact cleaner, scrub the male pins of each and every connector.  Then plug and unplug the connector  a couple of times so as to wipe the female contacts. Do this one at a time and double check to see each connector is inserted fully and correctly.
>>>
>>> NEVER NEVER NEVER spray anything into the radio.   {One fellow I know [not me] removed the plugin IC's, sprayed into their sockets, and now he has a radio full of issues and weirdness.   Remember contact cleaner is used to promote the flow of current.   Imagine what takes place in a logic IC socket that is wet with cleaner. ugh!!!! }
>>>
>>> With a radio of that age, it not at all unusual for the electrolytic caps in the audio stage to deteriorate.  One issue which can exist is the output of a stage can drift negative a few millivolts.  In effect it will reverse polarize the coupling capacitor.  The result is after time the 1 MFD cap will migrate to about 0.01 MFD.  Not a good path for audio in these circuits. Makes the radio sound funny too.     I always replace the audio coupling capacitors with nonpolar electrolytics of the same voltage and C value.   There is no need to change parameters. Problem solved.  I had a lengthy discussion with Tentec management and engineering on the subject some years ago.   It almost caused me to not buy a new Omni VI Plus.    Finally, I did and loved it.
>>>
>>> Hope this helps.
>>>
>>> 73
>>>
>>> Bob, K4TAX
>>>
>>>
>>>> On 9/17/2018 8:00 PM, Stan Gammons wrote:
>>>> Hi All,
>>>>
>>>> I was tinkering with an old D-104 T-UG8 that I had put a Heil conversion kit in since the original element bit the dust. I ask for an audio report from some of the locals that know what I sound like and they said I sounded terrible.  So, I switched to the Ten-Tec 707 mic, same report. So, I tried my trusty old EV-638. Same story.  I didn't try it with the converted D-104 to see what it sounds like. They initially told me it sounded like the mic was picking up something like a fan maybe, so turning the gain down helped a little but not a lot. SO, today I decided to put the Omni VI on a dummy load and listen to it with my Drake TR7.  Yuck! The Omni VI sounds terrible!  It's almost like there is a little bit of a carrier and it has what sounds like digital hash on it. It gets worse the higher the mic gain is cranked. When I modulate, the audio sounds all distorted. Even without modulation, if I turn the processor on and crank it up, the digital hash in the audio seems to get even wo
>   rse. SO, just to make sure it wasn't something weird going on, I did the same thing with the TR7.  I put it on a dummy load and listened to it with the Omni VI. I tried it with the same mics and the audio is clean. No hash or anything.  Anyone heard of a problem like this with an Omni VI?
>>>>
>>>> 73
>>>>
>>>> Stan
>>>> KM4HQE
>>>>
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