[TenTec] LONG: Audio improvements on Argonaut VI

[Greg S]

The audio amp is a TDA1013B, which has been discontinued, but is available at surplus.
Regards,
Greg, KC8HXO 

Sent from my Linux device

> On Aug 25, 2018, at 05:23, Carlos <carlos.peco at gmail.com> wrote:
> 
> 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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