Computer speaker transformer

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a_dam

a_dam

New Member
Feb 21, 2009
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Momence, IL
Haven't rode for weeks - too cold - so I'll post a stupid question.

I just bought some used Harman Kardon speakers. Good shape, look new. Got them and a PS2 mouse for 10 bucks from a shop that sells new and used equipment.

While checking them out more closely at home, I noticed that the speaker's transformer is rated 15V and 1.1 milliamp. Kinda unusual, as all other cheap speakers I've had/seen used 12V DC.

I went to test the actual output voltage with a multimeter and couldn't get a reading. It would show maybe a couple volts for a split second when the probes first touched, but then drop back down to zero. (the transformer is working - it powers the speakers fine)

So I checked some other various wall-warts I have (3V, 12V, 30V...). Some show a steady voltage as I would expect, but some act like the 15V harman kardon. I know that they all work.

Do some transformers need a certain amount of load in order to output power?
 
Last edited:
a_dam

a_dam

New Member
Feb 21, 2009
351
0
0
Momence, IL
Nevermind.

I couldn't get a reading because the output is AC; 15VAC, 1.1 A (not 1.1mA of course). All my other computer speakers had DC power supplies, so I assumed this was as well.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Coincidently, I was listening to an audio book yesterday on my old computer with the same HK speakers you probably have, when I heard a 'click' and the sound went off. I checked a couple of things, red power light on the transformer was on but the speaker power light wasn't. I checked the output voltage of the transformer (power supply) and it was zero. On the transformer 'were' two small yellow knobs. One set the output voltage, the other set polarity. The knob for the volt selector was...gone. I found it under my desk. I disassembled the transformer and found the knob's shaft had snapped apart and the spring that held the contacts tight had propelled the top of the knob upwards hitting the underside of the desk...hence, the 'click' sound.
I didn't have another power supply, 15VDC, but I found one, same plug, that was 4.5VDC. I checked the output and it was in fact 5.2. I plugged it in and the speakers work. I suppose they aren't too voltage sensitive.
Tom
 
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