Electronical question

[TommyK]

I acquired a used set of computer speakers. They did not have the 9V transformer, but I had one at home. The speaker case, next to the power input socket, is clearly marked "9V". The transformer (brick on a wire) indicated 120V input, 9V output. I plugged it all up. In short order the speaker with the amplifier began to smoke. I opened it up and it appears it over heated a couple of the tin-can capacitors on the bread board. They were almost too hot to touch and a hot waxy substance was dripping out of one. I put a VOM meter on the output end of the transformer. It read just a hair over 11V. Wall outlet voltage is exactly 120V.

 

I checked a few other power transformers, from other working appliances at home. They all read a volt or two over their labeled voltage. Did I blow my speaker amp due to being 2 volts over? or is something else wrong?

[grampa]

Polarity. You may have had it backwards.

[yoda]

Polarity. You may have had it backwards.

 

 

I second that. Most wall adapters are +10%-40% volts and will not blow anything up, but wrong polarity will.

[Riverside]

AC, or DC voltage?

[Riffster]

I agree with the polarity, power transformers for guitar pedals have reverse polarity right? center is negative.

 

If you used a pedal transformer that may have been the problem.

[milod]

And... there are transformers and there are transformers.

 

A number of devices requiring them will have specialized transformers that won't feed too much into the device. Electricity is more than a matter of volts.

 

m

[SHO]

You have to put a load to the transformer when checking its output voltage. The meter alone is too high impedence to count as a load, and with so little current passing through the transformer you won't get an accurate reading. But even if the transformer did indeed put out 11V, I really doubt that would blow the speakers.

 

I also doubt polarity is the case. Avoiding polarity problems is as easy as adding a diode to the input so current can only pass one way.

 

I'm curious, does it say anywhere on the transformer how many ampere (in A or mA) it can put out, and does it say anywhere on the speakers how many they draw?

[Blackie]

Polarity, milliamps, ..........

[TommyK]

...I'm curious' date=' does it say anywhere on the transformer how many ampere (in A or mA) it can put out, and does it say anywhere on the speakers how many they draw?

[/b']

 

I'll check on it and report back

[mcmurray]

I'll go out on a limb and say your transformer has an AC output, and the speakers require DC.