[TenTec] Omni VI audio problem
Bob McGraw K4TAX
rmcgraw at blomand.net
Tue Sep 18 22:55:12 EDT 2018
I've found typically the mike gain runs 9 o'clock to 10 o'clock on these
radios. Yes the 707 has much lower output and will require one to
raise the gain a considerable amount. My 707 sits on the shelf with my
original D-104. They "look good" sitting there, which is where I
prefer they remain.
I fought the computer interface issues to my Paragon and my Omni VI
series. Both have the same type of input on the rear where the mike
audio and the rear connector audio are summed together through a pair of
47K resistors on the TX audio board.
The better solution I found was to build a resistive L pad with about 20
dB loss. The 1/8 watt resistors were mounted in the shell of the RCA
connector which plugged into the rear connector. This required I
raise the level out of the computer sound card but in doing so, I
improved my transmit S/N ratio about 20 dB. This is worth doing
regardless of your final decision. Makes for cleaner digital signals and
allows easier adjustment of the audio out of the computer for transmit
level control. This allowed me to keep the mike gain at the 9
o'clock position. Just be sure the mike connected to the front is off
so that any room noise being picked up is not transmitted.
73
Bob, K4TAX
On 9/18/2018 9:43 PM, Stan Gammons wrote:
> For now I'm just going to disconnect the sound card output from the PC
> when operating phone. I did try another core at the sound card output
> and for some strange reason that made matters worse. One core on each
> end of the cable reduces the hash/noise a lot. Only when I have the
> mic gain around 1 o'clock do I notice the increase in output when I
> have the rig keyed without a mic attached. Normally, I run the mic
> gain around the 9 o'clock position. I don't believe Ten-Tec 707 has
> as high an output as the Electro-Voice EV-638, but 9 o'clock on the
> mic gain seems to be Ok with either mic. The 707 is pretty, but I
> like the EV-638 as much or more.
>
> I don't have the PC chassis bonded to station ground. I'll mess with
> that this coming weekend.
>
> Thanks for all the replies.
>
> 73
>
> Stan
> KM4HQE
>
>
> On 9/18/2018 9:25 PM, Greg S via TenTec wrote:
>> Run both audio sources in the back. Switch between them with a
>> conveniently mounted DPDT switch. These rigs ain’t worth much any
>> more. I little hole, or a bracket added somewhere isn’t gonna kill
>> what little value they have left. I like mine, but have a few
>> tinkerers mods slated for the upcoming winter months.
>> Kind regards,
>> Greg, KC8HXO
>>
>> Sent from my Linux device
>>
>>> On Sep 18, 2018, at 09:29, Bob McGraw K4TAX <rmcgraw at blomand.net>
>>> wrote:
>>>
>>> Even with that approach, any noise coming out of the computer sound
>>> card output stage will be sent to the input of the Omni VI. This
>>> will occur even when the audio gain of the computer is reduced or
>>> muted as the gain control is before the output stage of the sound
>>> card. Just the fact, any noise coming out of the computer will be
>>> introduced into the MIC audio due to the design of the circuit.
>>>
>>> One can add some 20 dB of attenuation in the form of an L Pad
>>> between the output of the computer and the input to the radio. This
>>> will reduce the amount of noise to perhaps a satisfactory level.
>>> But still, there will be some noise coming from the computer sound
>>> care, reduced 20 dB. And one will then need to raise the gain of
>>> the data signal in the computer application to off-set this 20 dB
>>> attenuation. While I find this works and I operated this way for
>>> years, the digital artifacts from the computer may still exist to
>>> some lesser extent, although may be found to be satisfactory.
>>>
>>> The best solution is to disconnect the cable to the rear input when
>>> not used. But when used, you will still likely need the 20 dB
>>> attenuation to clean up the digital noise out of the computer. A
>>> Transformer is an OK idea as long as it is configured to have
>>> voltage loss and not matched loss. The idea of the transformer is
>>> to eliminate a "ground loop" what ever that might be. {The only
>>> ground loop I'm familiar with is upon less than a careful landing
>>> of a Piper Tripacer in a cross wind.}
>>>
>>> 73
>>>
>>> Bob, K4TAX
>>>
>>>
>>>> On 9/18/2018 4:50 AM, Barry N1EU wrote:
>>>> Stan, to get rid of the residual hash do one of the following:
>>>>
>>>> 1. assure you have the computer chassis and Omni 6 chassis properly
>>>> bonded
>>>> to common station ground.
>>>> 2. put an audio isolation transformer in the line between PC
>>>> soundcard and
>>>> Omni 6 audio in
>>>>
>>>> 73, Barry N1EU
>>>>
>>>>> On Tue, Sep 18, 2018 at 2:41 AM, Stan Gammons
>>>>> <s_gammons at charter.net> wrote:
>>>>>
>>>>> 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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