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Audio (and aftermarket electronics) This is your place for alarms, remote starters, to brag about your system, exaggerate your db levels, or simply ask questions for stock or aftermarket audio. No Flames! (except from roasted amps)
View Poll Results: What should i do with this amp?
Buy replacement parts and give it a go? (Cost: $10)
75.00%
Put my money towards a new amp? (Cost: $200)
25.00%
Voters: 4. You may not vote on this poll

Help, smoke! Fixed once. New Pictures!

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Old 06-28-2007, 04:32 AM
  #11  
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I want to revise my earlier observations. I wish we had a schematic to know for certain, but those Mosfets that blew -I'm now pretty sure those are in the switching power supply portion of your amp. Not the output (audio) driver transistors. (Which can also be Mosfets, but not as common.) And thus, my diagnosis of "you probably had shorted output" is no longer valid. I think your output is fine.

Brief description of car amps: They incorporate a rapidly switching power supply -using a signal timer to rapidly turn on and off current to the Mosfets (which switch very rapidly), making a "chopper" circuit, or 12-volt DC square wave, which drives that donut-looking toroid transformer. The output of the transformer is a much higher voltage squarewave, which can be rectified and filtered to produce a "greater than +12V" power supply. Typically more like 50 volts, center-tapped for +25V and -25V (or more) used to drive the audio amp circuit.

Like any transformer, the voltage gain comes at the expense of current loss, so the INPUT current into a car audio amplifier'* switching power supply is, in a word, -enormous. That'* why there'* a big fatty fuse on that thing with some large amp rating of like 25 amps or possibly quite a lot more.

Anyway, the Mosfets that blew appear to be in the switching power supply circuit part of your amp, and that would indicate that the output section was probably not the source of the problem. (It doesn't guarantee it, but it'* a pretty good generalization.) -And thus I'd say that when you transmit from your ham radio at full power, it does wonky things to the car amp'* power supply for some reason -either faulty wired connections or just strange interactions that ham radios have -I have no experience with ham radios, and so I'm really at a loss to take a stab at how it could have fried your amp. But it'* pretty clear that it DID, at any rate!

My recommendation: Don't do that again!
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Old 06-28-2007, 12:47 PM
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Originally Posted by Bugsi
I want to revise my earlier observations. I wish we had a schematic to know for certain, but those Mosfets that blew -I'm now pretty sure those are in the switching power supply portion of your amp. Not the output (audio) driver transistors. (Which can also be Mosfets, but not as common.) And thus, my diagnosis of "you probably had shorted output" is no longer valid. I think your output is fine.

... That'* why there'* a big fatty fuse on that thing with some large amp rating of like 25 amps or possibly quite a lot more.
Yep, thats 60 amps of electrical fire right there. I am going to run some tests with the o-scope to see just how much Radio Frequency (RF) that sub/wire combination can pick up. Then Ill look at the power lines to see what it does to that.

If all else fails ill just have to assume that the amp internals couldnt handle the ity-bity bit of radiation that would have made it through the casing of the amp. Eventually i need another amp and I want to make sure i dont do this to the new one.


Originally Posted by Bugsi
My recommendation: Don't do that again!
Thaaaaaanks.
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