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vputz 15th August 2012 04:24 PM

My gainclone ate my mp3 player?

I built a basic "reference design" gainclone (one power supply, two channel sections) which worked well and sounds great connected to my econowaves. There's a "turn-on" thump, but I never thought much of it (I'd like to fix it, but it's low priority since I'm about to move and the workshop is being disassembled).

However, I have a more pressing concern. I hooked up my MP3 player and played a track; it worked fine until I shut down the amp first. My mp3 player now appears to be bricked. Is it possible there's enough spike feedback through the line in that it fried my player? If so, how would I diagnose and fix this?

djoffe 15th August 2012 06:05 PM

It would be good to know the output impedance of your MP3 player, but failing that, we could assume 100 Ohms.

Connect 100 Ohms between the input of each gainclone channel and ground. Connect a digital scope, properly triggered, say at about 1/2 volt positive or negative. Then turn the gain clone on and off a bunch of times, try to capture the waveform across the 100 Ohm resistor. If you get much more than 1 Volt (either polarity), you probably have a problem.

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JRKO 15th August 2012 06:18 PM

did you use a line out level or headphone jack out?

If you used your headphone out you could have fried the opamp thingy:scratch:

kctess5 15th August 2012 06:35 PM

Something similar happened to me. Not with my gain clone though, no issues there.

Last thursday I was troubleshooting a pair of active speakers I made and I thought one of the amps might be the problem, so I wired it up like you're supposed to, turned it on, and poof my Macbook was dead.

I brought it in and they said they thought it was the logic board. $300 dollars to fix, and its 4 years old. So nearly $1500 later I'm replying from my new mac

johnr66 15th August 2012 07:19 PM

I've never seen this unless the amp circuit has an issue. I blew my CD player's output after building an amp. I tie the ICs direct to the heat sink for the best thermal conduction, but of course, that puts the negative rail on the sink. During assembly, I somehow pinched the input wire against the heat sink and you can guess what happened!

vputz 15th August 2012 11:09 PM

Huh, it's a puzzler still. I hooked it up to an O-scope at work as djoffe suggested, but after attempting several power cycles, I never saw a peak-to-peak voltage difference of greater than 250 mV, and by far most of them were about 46 mV. Could my speakers have been at fault? I can't see how they'd feed back through everything, but I guess one never knows.

Curiouser and curiouser. I'm not dying to hook up my computer to this system yet, I can say that much. Visually all the appropriate groundy bits are tied to ground. Huh. Any other ideas?

JRKO 15th August 2012 11:18 PM


Originally Posted by JRKO (
did you use a line out level or headphone jack out?

johnr66 16th August 2012 12:59 AM

Your MP3 player could have simply died on its own. Is there a way to reset it, such as holding a button down or a small reset button hidden on the player somewhere?

DigitalJunkie 16th August 2012 06:58 AM

There are a few GOOD reasons to use coupling caps,This is one of them.
I learned the hard way,just like you.

picowallspeaker 16th August 2012 07:02 AM

Me too .
And also keep sure of connecting the ground wire to amp's input .

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