If the players battery powered then the ground assumes whatever potential it happens to connect to. 0 volts or a 1000000 volts it doesn't matter. No current flows. If the player is AC powered then its a whole different ball game.
30 volts at 30 ma doesn't seem much but consider a CMOS chip running at 3.3 volts that draws a micro amp or two. It would certainly zap that.
We'll probably never know what really happened with this one. All we can do is make best guesses as to the most probable scenarios and design to try and avoid that.
Thanks, Mooly. I just spent another fair amount of time in the lab checking continuity of ground et al, doing O-scope traces of the input and output lines, etc. It looks great still. I may just make a "line in condom" with the caps and resistors and some rca jacks until I have time to fix the circuit proper.
The player is (was) indeed bat powered. Ah well. I was getting tired of it and its proprietary connector anyway, so a replacement was coming; this just gets it here a bit sooner.
The player is (was) indeed bat powered. Ah well. I was getting tired of it and its proprietary connector anyway, so a replacement was coming; this just gets it here a bit sooner.
Taking my new MP3 player's life in my hands, the amp works just as well as it ever has... but when I turned it on, the UPS connected to the same circuit cycled (with speakers but no input attached). I've got a wicked powerup/down thump issue. Guess I need to learn a bit more before recommending this to friends 
I recall reading datasheet from a Wolfson IC intended for mp3 players suggesting a certain output implementation to avoid the headphone out (some class d amp) from going unstable when connected to a high impedance load like the imput of your gainclone.
Maybe the manufacturer cheaped out and that's what happened here?
Maybe the manufacturer cheaped out and that's what happened here?
I don't think inrush current is the cause of the mp3 zap, but I do think it was what cycled the UPS. Honestly with the transformer only being 250-350VA, inrush isn't even a big worry so much as an annoyance and I can live without soft start on this if I need.
Still need to make my input decoupler, though.
Still need to make my input decoupler, though.
Irritating addendum:
It got better. I'd made the filter dingus (Mooly, I made a hacked version with too-small caps, and I think it was proof of concept; passed signal well and periodically fuzzed out; I'll try with proper parts at some point), and was listening to music through a new MP3 player, when as I went to toss out the old one I tried power again. Works like a champ.
So, I'm healthily in WTF mode, and still puzzled, but I suppose I should count it as a blessing.
It got better. I'd made the filter dingus (Mooly, I made a hacked version with too-small caps, and I think it was proof of concept; passed signal well and periodically fuzzed out; I'll try with proper parts at some point), and was listening to music through a new MP3 player, when as I went to toss out the old one I tried power again. Works like a champ.
So, I'm healthily in WTF mode, and still puzzled, but I suppose I should count it as a blessing.
I have come across a few cheap mp3 players, that need a fairly low resistance load to function. They often use the headphone load as part of the filter circuit.
Maybe the player went into protection mode as the output caps charged up.
I always fit a bleeder resistor anyway at the input of any amp.
Are you using a SMPS to power the amp ? Often these outputs will float at about 1/2 mains voltage. then add in the -3000v of static from your hands and poof!
Maybe the player went into protection mode as the output caps charged up.
I always fit a bleeder resistor anyway at the input of any amp.
Are you using a SMPS to power the amp ? Often these outputs will float at about 1/2 mains voltage. then add in the -3000v of static from your hands and poof!
Whizgeek: it's not an SMPS, it's a simple toroidal transformer with a diode bridge and caps (a bog-standard "gainclone power supply" as shows up in a number of places).
I'm still puzzled. The silly thing looks like it's operating fine now, but it was completely insensitive to the power switch for about 3-4 days.
Good point on the bleeder resistors too. I'll take a look and edit, although as mentioned it seems to be all happy again. Bizarre.
I'm still puzzled. The silly thing looks like it's operating fine now, but it was completely insensitive to the power switch for about 3-4 days.
Good point on the bleeder resistors too. I'll take a look and edit, although as mentioned it seems to be all happy again. Bizarre.
I had the same thing happen years ago with a portable CD player that I used for testing (specifically because it was battery powered,and isolated).
No idea what happened,I can only surmise that somehow DC came out of the amp's input,and cooked the CD players output stage.
Ever since then I've used input caps,purely for DC-blocking,and haven't had any similar issues.
One other good thought is HF crap coming out of the MP3 player. I know my iPod has some noise and crap on the output. Perhaps your amp didn't like being fed some random several-hundered-khz signal. I dunno.
No idea what happened,I can only surmise that somehow DC came out of the amp's input,and cooked the CD players output stage.
Ever since then I've used input caps,purely for DC-blocking,and haven't had any similar issues.
One other good thought is HF crap coming out of the MP3 player. I know my iPod has some noise and crap on the output. Perhaps your amp didn't like being fed some random several-hundered-khz signal. I dunno.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.