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Line input direct to WM8731 pin 19

 

I have a mic and audio processor with line level output. Is there any reason I can't apply this directly to WM8731 pin 19 directly - bypassing the mic amp circuitry? I will use a 1:1 transformer to unbalance the output of the processor? I'd just try it, but am away from home at the moment, so I thought I'd check for any gotchas while I can!
73 de ZL1SGS
 

I should work. Just set the correct ALSA levels and knobs.

- Rafael

On 2/22/24 07:31, ZL1SGS wrote:
I have a mic and audio processor with line level output. Is there any reason I can't apply this directly to WM8731 pin 19 directly - bypassing the mic amp circuitry? I will use a 1:1 transformer to unbalance the output of the processor? I'd just try it, but am away from home at the moment, so I thought I'd check for any gotchas while I can!
73 de ZL1SGS

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Thanks - I'll give it a go over the weekend and report back.
 

Cool. Lets us know! Remember that if you are using Farhan's sbitx reference implementation, edit the mixer code to use the line instead of the mic input. Or just play with alsamixer (and any audio recorder) at first to see if you can read the signal.

Cheers,
Rafael

On 2/22/24 20:15, ZL1SGS wrote:
Thanks - I'll give it a go over the weekend and report back.

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Hi Rafael,
?
Curious about the ALSA mixer settings for the mic. For my home brew build, I built the mic amp from the SBITX schematic. I tack soldered in a electret capsule of unknown spec that I just happened to have in the junk box. I am getting some audio through but it doesn't seem very sensitive. With the microphone gain maxed I get a fair amount of noise on the waterfall from background noise. And I can see it on a scope at the output of the PA. But when I talk into the microphone I don't see much change. If I play a 1KHz tone from my phone with the phone speaker right next to the microphone hat comes through cleanly..

Any ideas or recommendations? Appreciated .
?
73, Dean
KK4DAS?


?
 

Have you added the bias resistor needed for the electret mic to operate?


On Fri, Feb 23, 2024, 7:39 PM Dean Souleles <dsouleles@...> wrote:
Hi Rafael,
?
Curious about the ALSA mixer settings for the mic. For my home brew build, I built the mic amp from the SBITX schematic. I tack soldered in a electret capsule of unknown spec that I just happened to have in the junk box. I am getting some audio through but it doesn't seem very sensitive. With the microphone gain maxed I get a fair amount of noise on the waterfall from background noise. And I can see it on a scope at the output of the PA. But when I talk into the microphone I don't see much change. If I play a 1KHz tone from my phone with the phone speaker right next to the microphone hat comes through cleanly..

Any ideas or recommendations? Appreciated .
?
73, Dean
KK4DAS?


?
 

On Fri, Feb 23, 2024 at 09:41 AM, Ashhar Farhan wrote:
Have you added the bias resistor needed for the electret mic to operate?
I built the audio anp directly from the schematic. It looked to me like RD21 at 10k was all that was needed.? What else do I need?
 

Hi Dean,

I already read Farhan's email (tks Farhan!) and your reply.

Nothing to add, and no solutions, but I also have some high level of noise with the stock sbitx + shipped mic (more than I wanted, lets say). Reading the WM8731 datasheet, there are some options for DC offset manipulation and others. I still had not time to play with them, but all these controls are available tru Alsa. I think it would be a good idea to play a bit with these controls and see what goes on.

73,
Rafael PU2UIT

On 2/23/24 14:09, Dean Souleles wrote:
Hi Rafael,
Curious about the ALSA mixer settings for the mic. For my home brew build, I built the mic amp from the SBITX schematic. I tack soldered in a electret capsule of unknown spec that I just happened to have in the junk box. I am getting some audio through but it doesn't seem very sensitive. With the microphone gain maxed I get a fair amount of noise on the waterfall from background noise. And I can see it on a scope at the output of the PA. But when I talk into the microphone I don't see much change. If I play a 1KHz tone from my phone with the phone speaker right next to the microphone hat comes through cleanly..

Any ideas or recommendations? Appreciated .
73, Dean
KK4DAS


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On Fri, Feb 23, 2024 at 09:41 AM, Ashhar Farhan wrote:
Have you added the bias resistor needed for the electret mic to operate?
Electret microphone capsule problem solved.? It was cockpit error on the part of the builder (that would be me).

In brief - when I finalized the mic amp build I mistakenly powered it from the 5V rail instead of the 12V rail.? I had read through the long thread from last year on electret bias and the recent thread on SSB audio quality?and had ordered a ag of the -25dB capsules that Gordon recommended.? They accept VCC of 2-10 V through a 2.2K resistor.? So replaced the R21 10K biase resistor with 2.2K to the 5V rail.? With that setup the mic is working great.

Now on to the next challenge - getting trransmit clean end-to-end.

73,
Dean
KK4DAS
 

Just to round off my original question - feeding line level directly into pin 19 works fine. I now have the option to use the original mic input with electret mic, or line input and just use the mic socket for ptt. I didn't mess with alsa settings - just set my line level to about -10 to match domestic line level input of the a-d.
 

With the version two sBitx and its standard amplifier and the high output -25DB electret Mic, I noticed I had to turn the mic gain all the way down to 15 today! With a lower output Mic I have it turned up past 25.

You can make anything work if you just adjust gains appropriately.

More power to you. Gordon

On Feb 28, 2024, at 19:34, ZL1SGS <goresmith@...> wrote:
 

Thanks for letting us know. Cool!

On 2/29/24 00:18, ZL1SGS wrote:
Just to round off my original question - feeding line level directly into pin 19 works fine. I now have the option to use the original mic input with electret mic, or line input and just use the mic socket for ptt. I didn't mess with also settings - just set my line level to about -10 to match domestic line level input of the a-d.

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