[Tightwad]

I built a mini3 headphone amp, the long life version, and the charging cord shorted against the case, and now the amp is very distorted. This creates a few questions...


What is likely to be bad, so I can replace it?
How can I prevent this from happening? I use it on a motorcycle, so I need to be able to power it while riding more than the 12 hour or so battery life.


Not quite as important, but still wondering...how can I configure it to charge on only 12 volts, instead of 15ish? It runs on 12, but doesn't seem to charge.

 

[m1abrams]

Most likely you killed U3 (TLE2426CLP precision rail-splitter TO-92). You probably have some severe DC offset now and should not use the amp as that could damage your headphones.

To prevent this in the future do not plug or unplug the power adapter when the amp is turned on. While it is properly plugged in I can not see it accidentally shorting. However if your clearance for the jack is really tight you may want to widen that hole a little bit more.

As for charging with only 12V supply that would require more components and can not be done by just changing part values. What you may be able to do is create a power supply that boosts your bikes 12V to 15V.

 

[Tightwad]

I will replace that component. The problem was not removing the charging plug, but rather it bent a bit sideways and contacted. I will look at methods to isolate that portion to prevent it from happening again.

 

[Billyk]

Shorting against the case always made me nervous, I made the hole around the charging socket large enough to accommodate the molded plastic part of the plug so when it's plugged in it cannot short against the case.
This works well. It did until I plugged in a 20VAC wall wart and fried C2

, at least it still works and replacing C2 was simple enough.

 

[Tightwad]

Got the Rail splitter chip ordered...I will look at isolating the back panel at that spot, not a good design to me, too many chances of shorting out.

 

[m1abrams]

Quote:

Originally Posted by Tightwad /img/forum/go_quote.gif Got the Rail splitter chip ordered...I will look at isolating the back panel at that spot, not a good design to me, too many chances of shorting out.

Well I do not think the design ever was meant to be charging while portable. I actually do not charge my mini3 while using it. For bike use I would probably just run off the battery, do you have many 6+ hour rides?

Other thing you could do is use plastic end plates instead of metal ones, find a rubber grommet to fit the whole, paint the hole with the rubber stuff they use to coat tools, etc. Remember this is DIY so you make the item fit your needs, AMB just gets you started with a solid design.