[TenTec] LONG: Audio improvements on Argonaut VI

[Carlos]

Hi Rick,

Success. I have been away for almost the entire week due to work
commitments (I'm very fortunate, my job involves HF receivers and direction
finders) but today I managed to put a couple of hours in the Argonaut VI.

- I connected an active amplifier to the Line Out connector, and none of
the digital artifacts or the tuning noise can be heard. - The hiss is
almost non-existent in the Line Out connector.
- I can amplify the audio to a very confortable level without any sign of
distortion.


So there a mixture of issues and non-issues in my radio. There is digital
noise in the internal speaker (you can only perceive it with quiet band
conditions and nobody around, or with the RF gain in the low side, or with
headphones) and, additionally, it might be that the internal audio
amplifier or the speaker need service because people sounds a bit distorted
when using the internal audio chain.

In any case, using the Line Out and a quiet external active speaker, the
radio is absolutely great.

On a side note, the noise blanker cancels with great ease the Chinese OTHR
radars on 20 meters. Really good.



So I'll be using the external active speaker and, one of these days, I'll
measure the THD generated by the internal amplifier to determine if I have
to change the audio chip or the speaker.


73,
Carlos VK1EA


On Tuesday, August 21, 2018, <Rick at dj0ip.de> wrote:
>
> " Even if a manufacture follows the device datasheets,
> there's still a variable that comes into play with circuit
> board layout and power supply decoupling. "
>
> FOR A TEN-TEC EXAMPLE:
>
> The Eagle has a similar noise problem when turning the Audio gain and RF
> gain down.
> The noise can barely be heard on the speaker but is loud and clear on
"some"
> headphones.
>
> Dave, KW4M, found and fixed the problem ON HIS EAGLE.
> I DO NOT RECOMMEND OTHERS TRY THIS . . . unless they are very experienced
> with soldering on SMD gear.
>
> A complete description of this mod can be found in Message #4477 in our
> Ten-Tec Eagle group on groups.io.
> ---------------------------------------------------
> Here is an excerpt from that message:
>
> The processor noise is being picked up at the input of op amp U9 on the
> DSP board.  More specifically, signals SPUMISO and SPUMOSI are routed
> very close to the input pins on this device.  These traces are routed on
> internal layers but are visible when holding the board up against a
> bright light.
>
> Eliminating the processor noise pickup into U9 will require a circuit
> board layout change to move these traces.  Perhaps TT will make this
> change sometime on future radios.  (Rick's Note:  they never did!)
>
> In the meantime, there is a fairly simple workaround.  Since the Audio
> Out stage U9 and the Line Out stage U11 are identical, these circuits
> can be swapped.  This change was made on my radio and the processor
> noise cleared up.  Actually, the noise is now being sent to the Line Out
> port but the PC sound card will not be annoyed by it.   [:)]
> ---------------------------------------------------
> And here is a link to see a picture of that mod:
> http://www.genebitsystems.com/david/LinkedPhotos/EagleDspFix.jpg
>
>
> Perhaps Ten-Tec was aware of it when they first shipped, perhaps not.
> But even if, it would have been expensive to redesign the circuit board
> layout, and would have caused a long delay in the delivery time of the
first
> radios.
> Since this noise does not normally impede reception in any way (under
normal
> condx), it is not a big issue - at least not for me.
> Worst case, some users might need to buy new headphones...or sell the
radio.
>
> I will not attempt the mod on my own Eagle, out of fear of screwing
> something else up.
> My old eyes are poor and my hands are not as steady as they once were.
>
> So in this case, it was not poor electrical design, but rather poor
> mechanical design.
>
> Cheers!
> Rick, DJ0IP
>
>
>
>
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