What is max safe mic input level?

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LearningLots
 

Posts: 25
Joined: 15 Jun 2022, 17:59

What is max safe mic input level?

Post by LearningLots »

Just curious as to what is the maximum safe input to the tr usdx mic input? Thinking about building a one transistor pre amp for an external electret microphone.
Was going to scope the electret output and set the preamp to maybe 50% more. But the cautious side of me thinks I better ask first. I believe the mic connects directly into the computer chip. I don't want to damage that.
Thank you.
Kojoe
 

Posts: 2
Joined: 08 May 2022, 16:15

Re: What is max safe mic input level?

Post by Kojoe »

I had to do a bit of digging and measuring .. and here is what I've found:

Input Mic Signal goes into PC2 Pin and it should stay inside of 1V peak-peak and not exceed 1.1V peak-peak.
I'd love to measure the SSB Power Output in relation to an Input signal as I have a feeling that the MIC input level should be lower than 1Vpp.
I've also measured AREF to be at 1.1V

Further test needed (?)

VA3WBK
LearningLots
 

Posts: 25
Joined: 15 Jun 2022, 17:59

Re: What is max safe mic input level?

Post by LearningLots »

Thanks for your efforts!
DL3MHT
 

Posts: 21
Joined: 14 Mar 2022, 09:46

Re: What is max safe mic input level?

Post by DL3MHT »

My experiments showed a maximum input level of about 175mVpp without additional distortions. I used my PC as audio generator and transmitted into a dummy load and checked the audio on a receiver sitting next to it, which was also connected to a different dummyload. Afterwards I checked the used Vpp with a scope.

I used the default firmware settings and did not test with TX drive 0. (Only found out about that later. ;) )
Did anybody try this yet?

There is definitely some fixed SW gain applied on the ADC data that reduces the usable ADC resolution but avoids the need for an external MIC amplifier.

I guess somebody could ask in the "Question to the developers" thread. Guido could tell us in 5 seconds. You can try your luck.
(Alas my question about the digital audio filters got immediately deleted, so i am not bothering anymore.)

So my unqualified "try & error" opinion is, that anything between 100 and 175mVpp will work fine with the default FW settings.

You guys are probably right that you can go up to AREF without any damage - maybe even up to 5V, but it will distort.

73 de Tobias DL3MHT
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