What happens when you supply too much voltage to an amp exactly?

Question

i have a microphone preamp from america that should be supplied witg 120 volts however i am in south africa where they use 230 volts. on the back of the amp it shows 120-250 so, i used an adapter and plugged it in. it worked for a few seconds then all the lights went off. obviously the thing is dead. i have opened it up to look for damage expecting to find a black wire or burnt thing that i could replace but everything looks fine so, what i want to know is this: what physically happens to the electronics when there is too much power and is it repairable? also, i know a fuse is there to protect the electronics from power surges but dnes a constant flow of too many volts count? thanks for any help.

Answer 1

If it is rated for 120-250 it should have run fine, the fault is most likely due to other causes. The fuse only stops the unit from draining too many amps during a short (mainly to stop the risk of fire). Over voltage will ruin the first component on the circuit that cannot handle the increase in voltage, if your lucky then it will blow out and save the rest of the circuit, if your unlucky that component will short and pass the current on to other components. On most devices there is usually a switch for 120 or 250 selection which must be set to the right mode.

Answer 2

Most likely you have killed the preamp's power-supply.  Modern preamps or other electronics use what they call a switch-mode power supply, and can run on any voltage, anywhere in the world, with no problems.  Older equipment that is still transformer based requires that you supply the correct voltage, and feeding 230v into a device made for the 110v market will result in TWICE the voltage being applied to the "Guts" of the device - the preamp in your case.  Generally speaking, most electronics can handle a small difference in supply voltage, but a 100% increase in the design supply voltage will kill most electronics. :p  You'd need to check the power-supply in the pre-amp, but this usually requires some advanced knowledge of electronics servicing and/or a circuit-diagram of the device in question, so that you can see how the power-supply in the unit is built.  Usually, there is voltage-regulation in the form of 7805 or 7812 regulator IC's, but it depends really on how this unit was designed - they might have used something else.  The fact that it died within a few seconds indicates it really was unhappy with the much higher input voltage. Fuses don't care about higher voltage - that is a common misconception: "The fuse will blow if the voltage gets too high."  Fuses are current-protecting devices, and you could feed any voltage from a single volt or so(or less), right up to hundreds of volts through them, and they won't blow - ever.  They will only blow, if the current drawn through them exceeds the rating of the fuse for a sustained period.  There is no such thing as "a constant flow of too many volts" - simply speaking, volts are relatively-constant, and current-flow changes depending on the load.  Check if there is a small, recessed switch somewhere near to where the power cord connects to the preamp(usually red in colour) - it will be labeled 115 on one side, and 230 on the other.  This switch MUST be in the 230 position in your case.  If it says 115, it's set for the wrong voltage.

Answer 3

basically it overloads the amp it doesn't always cause burnt wires and whatnot

but if u did supply it with 230 volts and it won't work anymore then i'd send it back its obviously a manufacturing flaw i'm sure they'd be more than happy to send u a new one