I was given a BA635 speaker system but it is missing the transformer/
power cord. I have a lot of 12 volt adapters (I never throw away a
working power adapter LOL) but I do not know the tip polarity or
amperage. Does someone have one or know the above info so I can see if
I have an adapter that would work safely with this speaker system.
I had written all the following text, when I should have
just been searching for pictures of the BA635 because by
looking at the pictures from an eBay auction I found the
answer.
The original PSU was 12V, 1500mA, AC output... so the power
jack has no polarity. There will be a rectification stage
inside the subwoofer so if you used the wrong polarity it
just wouldn't work, and you'd then use the other polarity.
Odds are the outer barrel is ground/negative as that is far
more common. Here's the ebay auction with the pictures.
http://cgi.ebay.com/boston-BA635-3-...oryZ3702QQrdZ1QQssPageNameZWD4VQQcmdZViewItem
Your 12V wart is certainly worth a try but as I mentioned
below the peak output will be reduced if your warts don't
have a fair amount of current, 1A or more would be most
suitable but just try what you have and see if it's loud
enough for your needs before distorting.
I'll leave the rest of what I wrote below just in case
someone else eventually comes across the post and needs a
way to identify these things on some other speaker set.
Tip polarity is "usually" with the outer barrel as negative.
That's how it's set up on any equipment intending to be
standard instead of proprietary. However, there are even
some speaker sets that use an AC wart then rectify it on the
speaker PCB, and though I have not reverse engineered them
far enough to be certain of it, I do not think they were
making use of negative (to ground) voltage potential
anywhere, it was probably just cheaper to use warts without
the 4 diodes and a large capacitor in them, saved about 20
cents.
Odds are good you can determine the tolerance of the speaker
set by examining the circuit board. By tolerance I mean
that just because it came with (whatever voltage wart it
came with), that doesn't necessarily mean you need to use
that voltage. If your voltage were lower than the designers
intended, on most of these integrated chipamp arrangements
it would just reduce peak output power capability, and it is
unlikely you would exceed the max voltage using a 12V wart
though if unregulated it would float up closer to 16V, and
yet the designers take this into account when specifying it.
Anyway, you can examine the circuit board to get the numbers
off the chipamp chip and consult it's datasheet. Sometimes
the chip is a DIP style and there is a heatsink "tab" on it
covering up the markings which may or may not be so easily
removed. You'll just have to look to know what you're
dealing with. Also note the capacitor markings,
particularly the largest ones besides thouse that might be
part of an output coupling to the speaker drivers. keeping
in mind that if they were using an unregulated 12V wall
wart, the rating of the power rail capacitors would be at
least 25V, while if they were only 16V rated caps, it's more
likely the wall wart was lower voltage like 9V.
One area of importance is going to be the current capability
- more is better. If it's a 12V wart, you'd get a fair bit
of sound if the wart were (around) 300-500mA, but ideally a
larger wart of 800+mA would be used.
As for confirming the polarity, with the circuit board
exposed you can follow the copper traces to the jack and see
where they go. Odds are high one of them goes to a large
capacitor which will have it's polarity marked. If you have
a multimeter you might also check continuity (actually
resistance would be better).
