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Vref and microphones - can wrong setting cause damage
Posted: Thu Aug 07, 2014 1:24 pm
by DavidCooper
I'm trying to complete my HDA driver, but there's one area I don't understand (and Google is not providing answers). There are three vref (voltage) settings available for microphones and headphones: 50%, 80% and 100%, so I'm wondering how the right one should be chosen for the microphone/headphone that the user plugs in and whether it's harmful to set the wrong one.
Re: Vref and microphones - can wrong setting cause damage
Posted: Tue Sep 16, 2014 1:09 pm
by KemyLand
Yes, It is REALLY harmful!
Re: Vref and microphones - can wrong setting cause damage
Posted: Wed Sep 17, 2014 3:01 pm
by DavidCooper
Well, I can't tell if you're being serious or if you're making fun of my lack of knowledge on this. I may have damaged a microphone, but I can't tell. Instead of being centred on 0, the wave is centred on -32767 and half of it is completely missing, but it may have been like that before. I'd have thought a microphone doesn't have any power put into it though from the machine side, only having a voltage generated in it by sound interacting with it, so it seems unlikely that I caused the damage, but I can't rule it out. I'm guessing that there's more of a risk with earphones where the voltage must be generated from the machine side, but I don't know if it's possible to damage them either. I suspect electromagnets are robust enough to handle double the voltage. So, my guess is that damage is not likely, but a guess is not good enough.
Re: Vref and microphones - can wrong setting cause damage
Posted: Wed Sep 17, 2014 3:59 pm
by KemyLand
You shouldn't guess.
As you already said, electromagnets are strong enough to resist a voltage peak, but remember the other component may become uncalibrated. Obviously the risk is greater with earphones
.
The electromagnets will survive, but the extra voltage will (if not uncalibrate the system) cause "strange noises".
This isn't a trivial topic; neither a well-documented one. Try it with cheap, minimal earphones to test, and it would be better if using a test-box machine.
Re: Vref and microphones - can wrong setting cause damage
Posted: Wed Sep 17, 2014 4:02 pm
by KemyLand
Note: I've already worked with electronics prototypes (including earphones, microphones) and tell you my experience
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What I know is that earphones DON'T get a always a raw current, but microphones yes. That's because they're like transistors, they must let some current pass, some not.
But when talking about PCs, I'm not sure. Maybe PC earphones have an extra current to control something, don't know...