Mixing up AC and DC speakers!!

[Jimbo bob]

Hi everyone,

An interesting thing happened the other day. A friend of mine brought a pair of new speakers to me and let me know that “the speakers have fried”. I let him know that the “frying” smell is probably from his AC adapter because it had a voltage rating of “110V AC at 60Hz” as an input on it and where I live, the mains provide 230V AC at 50Hz. However, I did not pay attention that that adapter was an AC/AC adapter not an AC/DC adapter. So I hooked my AC/DC adapter to the speakers and they worked fine. I was careful to make sure not to exceed the voltage and current limits, but it was only later when I noticed that on top of the speaker’s power input, it is written “AC”. I found that interesting as I thought usually speakers are fed DC power and the conversion from AC to DC happens inside the adapter not the speaker.

But then I became curious, do you have any ideas what happens if I were to hook up the “right magnitude” of AC voltage and current to a DC speaker? (Opposite to my situation). Also in general, what sort of consequence should I expect if I connect a “correct magnitude” of AC voltage and current to an appliance which is supposed to work on DC?

Many thanks in advanced!!!

 

[Harald Kapp]

A speaker per se is always driven by AC (never by DC) namely by the audio signal.

Your speakers obviously have a built-in amplifier, otherwise tey wouldn't need a power supply. This amplifier will not work off an AC power supply. It will require a DC supply. Therefore you'll find a power supply circuit (rectifier, buffer capacitor, voltage regulator) inside the speaker, too.
The rectifier creates a DC voltage from an AC input, but it will pass a DC supply in the same way (only 1/2 of teh rectifier is being used in that case).

 

[Jimbo bob]

A speaker per se is always driven by AC (never by DC) namely by the audio signal.

Your speakers obviously have a built-in amplifier, otherwise tey wouldn't need a power supply. This amplifier will not work off an AC power supply. It will require a DC supply. Therefore you'll find a power supply circuit (rectifier, buffer capacitor, voltage regulator) inside the speaker, too.
The rectifier creates a DC voltage from an AC input, but it will pass a DC supply in the same way (only 1/2 of teh rectifier is being used in that case).

Thank you Harald. So, if I connect an AC power supply to the amplifier, I would fry it, correct? What about other DC appliances? Are there cases where I can (by accident) connect AC power to a DC device and it keep functioning? If the answer is yes, but there will be some abnormal characteristics in the performance of the device, what would they be? Any examples would be much appreciated

 

[davenn]

Anything designed to have DC plugged into it will not work with AC into it and quite possibly will kill it

but as Harald said in the last sentence of his post, anything running of an input of low voltage AC from a plugpack will happily work you will loose around 0.7V as the voltage drop through one of the diodes in the rectifier circuit.
In some gear I purposely place a bridge rectifier on the input to a DC operated device. This gives the device protection against accidentally reversing the DC supply to the device. The bridge rectifier will ALWAYS give the device the correct polarity

Dave

 

[Jimbo bob]

Anything designed to have DC plugged into it will not work with AC into it and quite possibly will kill it

but as Harald said in the last sentence of his post, anything running of an input of low voltage AC from a plugpack will happily work you will loose around 0.7V as the voltage drop through one of the diodes in the rectifier circuit.
In some gear I purposely place a bridge rectifier on the input to a DC operated device. This gives the device protection against accidentally reversing the DC supply to the device. The bridge rectifier will ALWAYS give the device the correct polarity

Dave

Thank you.

 

[Harald Kapp]

Anything designed to have DC plugged into it will not work with AC into it and quite possibly will kill it

Right. It cannot be predicted what will happen unless you know the input circuit.

The other way round (plug DC into AC input) is also not guaranteed to work. Imagine the input circuit has a transfomer: it will only operate from AC as a transformer blocks DC. Therefore as said before: It cannot be predicted what will happen unless you know the input circuit.