I think I broke my computers audio - Page 1
Forum section: electronics / beginners

author: wlamb02
author_rank: Newbie
timestamp: June 21, 2015, 01:59:29 am
content: So i was messing around with the LM386 audio amplifier. I added an RC low pass filter (C 1000uf R 5Ohm)before the amplifier and it worked fine. Then I wanted to switch back to unfiltered audio so I put the alligator clip on the capacitor lead. The sound was crackling so I plugged in my headphones and now the right headphone has a crackling noise all the time. The computer is a MacBook Pro (13-inch, Mid 2012). Did I break something?

author: wlamb02
author_rank: Newbie
timestamp: June 21, 2015, 09:09:39 am
content: bump

author: Ian.M
author_rank: Super Contributor
timestamp: June 21, 2015, 10:11:19 am
content: The evidence suggests you have indeed broken something. Using a motherboard or laptop audio input or output for experimenting without a very carefully designed and constructed external buffer is unwise - USB sound cards are fairly cheap and can be treated as sacrificial devices. Changing connections with the circuit powered on and the computer audio lead connected was also unwise. Its likely that the 1000uF capacitor had charged up somehow and when you clipped the lead to it direct, you zapped the audio output.

author: wraper
author_rank: Unknown
timestamp: June 21, 2015, 10:38:38 am
content: Likely you destroyed an audio codec IC if it is connected directly to the audio output or an amplifier IC if it is present on the motherboard.

author: wraper
author_rank: Unknown
timestamp: June 21, 2015, 10:40:31 am
content: Quote from: wlamb02 on June 21, 2015, 01:59:29 amWho in the sane mind uses so low R and so high C for the RC filter.

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2015, 10:42:49 am
content: You fried an audio output chip, and if you are unlucky as well the on board multi IO chip as well, as it is connected there as well for detecting headphone insertion and line or headphone output levels. Not easy to fix, as the chip is small, and buried in the non removeable main board. Applecare might replace the motherboard if you have the extended support option, but if they do not cover it the Macbook is going to have no audio built in any more.Solution is to buy an external USB sound device and use it ( cheap at $2 for the simplest Skype dongle with mic and headphone outputs), and use a spare one for your sound experiments.

author: lewis
author_rank: Frequent Contributor
timestamp: June 21, 2015, 10:47:34 am
content: Looks like a trip to Rossmann Repair in NYC:http://www.rossmanngroup.com/

author: amyk
author_rank: Super Contributor
timestamp: June 21, 2015, 12:36:03 pm
content: What's the model number (the one that begins with A, e.g. A1278)? Find a schematic and take a look... chances are that you blew the amp and not the DAC itself. E.g. on an A1278 the lineout amp is a MAX9724A.

author: Deathwish
author_rank: Unknown
timestamp: June 21, 2015, 12:42:41 pm
content: Quote from: lewis on June 21, 2015, 10:47:34 amLouis makes me chuckle ..https://www.youtube.com/watch?v=fh4hpM8JyvM&feature=youtu.be

author: lewis
author_rank: Frequent Contributor
timestamp: June 21, 2015, 03:48:03 pm
content: Quote from: Deathwish on June 21, 2015, 12:42:41 pmMe too, I've learned a lot from his customer relations

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 21, 2015, 04:37:07 pm
content: Quote from: Deathwish on June 21, 2015, 12:42:41 pmWhoah, that's great!

author: Howardlong
author_rank: Super Contributor
timestamp: June 21, 2015, 04:54:06 pm
content: Quote from: wraper on June 21, 2015, 10:40:31 amI was thinking Zobel network, but on the output, not the input, and it's also not clear how R1 comes into the equation. Even then, if that is what it's meant to be, it's a lot of C for an LM386 snubber.