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Dead DAC / AMP?
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Old 13th February 2020, 12:09 AM   #1
xXBrunoXx is offline xXBrunoXx
diyAudio Member
Join Date: Jul 2016
Unhappy Dead DAC / AMP?

Hello, today I was testing out an amplifier kit . I was using my smartphone as audio source ( Sony xperia Z5). The amp was playing no problem, turned it off, hooked it up again later and you could barely hear something in the speaker, tried headphones on my phone, one channel sound perfectly fine the other ( the one that was hooked up on the amp) I could barely hear it.
I wonder what might happend, the amp has input decoupling caps so DC shouldn't got into the phone's jack. (Sadly i learned this the hard way, I've damaged two other phones a few years back because of this on my diy experiments with amplifiers as I was a noob didn't knew caps block dc going back into your audio source.)
But how did it happen again, I measured 0v DC at the jack, 5v before the caps. So no Dc into the phone, AC from the negative feedback could go into the audio source? Is this what happend? I don't want this to happen in the future, I don't know what I did wrong.

The two phones from the past, sounded very distorted but still loud. This time no distortion but very very weak signal.

I Have killed the headphone amp(if it has any)or the DAC ( if it has one or it uses the DAC itself in the snapdragon processor.
Do you guys think if a mobile phone repair center can fix it , or they have to replace the whole damn mainboard/ motherboard?.
I' ve posted here because i couldn't find anything similar on the web,

Last edited by xXBrunoXx; 13th February 2020 at 12:11 AM.
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Old 13th February 2020, 09:34 PM   #2
xXBrunoXx is offline xXBrunoXx
diyAudio Member
Join Date: Jul 2016
Looks like on high resistance 10k + loads like an amplifier both channels sound the same volume, only on low resistance loads like headphones one channel sounds very weak, thank God it works , i don't really care about headphones since I use Bluetooth on the phone but I was mad because i use the phone on my main amp/ speakers since its output quality is great.
So I might fried the headphone amp inside the phone but only that. Might the phone "see" if the load is high resistance (amp input) and outputs signal directly from the DAC, and when it "sees" low resistance, headphones
It outputs from the headphone amp?.
Might make sense, if it always outputs from the class d headphone amp inside, signal wouldn't be so great for feeding amplifiers, I might be wrong, but, Do someone have some knowledge about this? i cant find anywhere.
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Old 14th February 2020, 07:30 PM   #3
Mark Tillotson is offline Mark Tillotson
diyAudio Member
Join Date: May 2018
Location: Cambridge UK
Hard to say anything without any information on your circuit.
I was testing out an amplifier kit
Care to give us details of the kit? Maybe photos too?
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