Monday, June 20, 2011

How to repair Amplifier?

So, you've replaced some parts in an amplifier, but are afraid they'll blow again if you missed something...
Here's a rig that's saved a lot of amps from a second death!
Build a box where you have the main power coming in from the outlet, and on this box, put a lightbulb socket, and a power outlet.
Wire these in SERIES.
plug the box into the wall, and plug the amp into the box.
The lighbulb will not only dampen the turn-on power surge, but if something is overloading in the amp, the lighbulb will start glowing as it drops the voltage to the amp - and in doing so, saving the fuses and components.

If the light is glowing bright with no signal going in, the amp is using way too much current - pull the plug, something surely is wrong...but you just saved a fuse! and probably several components!

At turn on, the light should light partially for a very brief period of time then go out essentially becoming nothing but a wire, and allowing the amplifier to operate normally.
For most amplifiers, I recommend about a 60W - 100W bulb at 120V for Canadian and US units.

NOTE**** If the amp is blowing fuses even with this rig in place, lower the wattage of the bulb. ****

Remember, if you see that bulb glowing steady, PULL THE PLUG.
Better yet, incorporate a light switch into the unit (also in series) so you can turn the power on and off at a moments notice !

Now to burn in your amp once it's working...
They are hard to find, and you may have to make your own by wrapping transformer wire around an aluminum rod or some such thing, but either find or make an 8 OHM coil. Use this rather than speakers to run high volume tests.
The lighbulb should start glowing to the beat.
At this point, scope the outputs to see if they are clean and not distorted or riding a DC voltage.
If all looks good, shut down, plug it into the wall, and go back to your high volume testing.
CAUTION - your resistor may get very hot! DO NOT run this test unattended!!!!!
After 30 minutes or so of stress testing the amp, check again to make sure the outputs are clean and DC free.
If everything looks OK, check the impedance of your speakers to make sure they aren't blown. Open or less than rated impedance means a blown or partially blown (and likely defective) speaker !
If the speakers check out, go ahead and hook them back up, and this will work.

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