[TenTec] Omni VI audio problem
Stan Gammons
s_gammons at charter.net
Tue Sep 18 23:15:45 EDT 2018
Yes, 9 o'clock on the mic gain seems to be about right for the EV-638.
Think I'll put the 707 on shelf next to that Vibroplex bug... :) I may
tinker with the converted D-104 some more. I think the Heil conversion
uses the HC5.1 element. Not sure how that element will work with the
amplified D-104's.
I'll try the L pad and bonding the computer chassis to station ground.
Thanks Bob.
73
Stan
KM4HQE
On 9/18/2018 9:55 PM, Bob McGraw K4TAX wrote:
> 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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