Thread: Portable speaker question

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So I found a nice JBL portable speaker (12V/1A) at the local thrift shop and tested it out with two seemingly compatible wall-warts (12V/1A and 12V/1.2A), but all I get is annoying humming sound when the speaker is either on or off.

I found the power supply specs online, and they seem to match that of the wall-warts, but no audio is output--just a humming.

Any guesses as to what the problem might be?

well in the meantime of coming up with an answer (gosh its been a long while for this stuff for me) have you opned them up to see if anything is loose or not attached correctly?

Do you know what the speakers' polarity requirement is? If the power plugs on your warts are center-positive and the speaker is expecting center-negative, you'll get that 60-cycle humming sound.

Were these speakers used when you bought them? That may be why they were at the thrift shop.

I think Otaku may be right. The polarity of the wall-wart is center-positive, and the speaker may require a center-negative power source. Is it possible (or advisable) to modify the wall-wart by cutting off the connector and rewiring it to reverse the polarity?

I dont see any problem with it.

Originally Posted by Haunter

I think Otaku may be right. The polarity of the wall-wart is center-positive, and the speaker may require a center-negative power source. Is it possible (or advisable) to modify the wall-wart by cutting off the connector and rewiring it to reverse the polarity?

shouldn't be a problem. In fact I had one of those multi-function type wall worts. In order to change polarity, al you did was flip the tip 180 degrees. Rewiring would do the same.

Rewiring is no problem, I do it whenever I need to switch polarity on a wart. Just give yourself enough wire to work with when you cut off the tip, and verify the polarity with a meter or an LED. Sometimes one wire on the wart will have a dashed line on the insulation - this usually means its the negative wire, but that isn't always true.

So I rewired the wall-wart and plugged it into the speaker and, lo and behold, the humming was gone! But a second after turning on the speaker, I noticed an unpleasant smell inside the speaker (never good) and the green light faded to black... I think I may have fried the board and will have to send the speaker to its final resting place for scrap parts. Ah, shucks!