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Old 11th April 2011, 01:48 AM   #1
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Default Rockford Fosgate Power 450S

Hello I have a Rockford Power 450S. One channel was defective as well as the power supply. I repaired the power supply and all is well with that. I repaired the defective channel only to find DC on the speaker terminal. I found 2 resistors on the board out of tolerance. I replaced them and the DC was gone. The amp powers up fine, but when the speakers are hooked up ESPECIALLY if the volume is up a little it lets out a extremely loud tone through the speakers. While it does this it draws about 20amps, then returns to normal. Aside this problem the amp produces nice, loud, and clear audio on both channels. It will play on the bench for hours with no issues. The amp does not draw excess current after the initial power up issue. If no speakers are hooked, it powers up normal without any issues.

Anyone have a clue here, I am lost.......thanks again
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Old 11th April 2011, 03:28 AM   #2
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Do you have any DC (no speakers connected) at the time when it would squeal?

If you drive a sine wave into the amp into a load, do both channels clip squarely and symmetrically (above/below the reference line)?
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Old 12th April 2011, 12:15 AM   #3
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Quote:
Originally Posted by Perry Babin View Post
Do you have any DC (no speakers connected) at the time when it would squeal?

If you drive a sine wave into the amp into a load, do both channels clip squarely and symmetrically (above/below the reference line)?
I have no dc with no speakers connected at the time it would squal. It does not draw the excess current without speakers hooked up either.

I am not sure what you mean by clipping squarely and symmetrically.

Viewing the output on the scope both channels look the same. The only thing that changes is the amplitude when you increase the volume. The amplitude is symmetric above and below the baseline on both channels. I didnt see anything square at all.

Originally I replaced the ouput fets in that channel, gates, emitters, and I also replaced two resistors that were out of tolerance. Those were R165 and R166. Those 2 made the DC go away on the terminal. Until those were replaced, it would short when a speaker was hooked up.

Any thoughts?

Last edited by seankane; 12th April 2011 at 12:16 AM. Reason: spelling
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Old 12th April 2011, 01:09 AM   #4
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If you don't see the tops clip off, you're not driving the amp to clipping. Driving it to clipping can sometimes lead you to the problem (if you find that the top/bottom of the waveform doesn't clip squarely).

I'd suggest that you replace the N version of the outputs before you do any more troubleshooting. They may not be the problem but they've been known to do strange things.
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Old 12th April 2011, 01:21 AM   #5
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Quote:
Originally Posted by Perry Babin View Post
If you don't see the tops clip off, you're not driving the amp to clipping. Driving it to clipping can sometimes lead you to the problem (if you find that the top/bottom of the waveform doesn't clip squarely).

I'd suggest that you replace the N version of the outputs before you do any more troubleshooting. They may not be the problem but they've been known to do strange things.
I already replaced all the output fets with IRF540 and IRF9540.

How do I drive it to clipping. I head the head unit volume to max of 30. The amplitude on the scope just keeps getting bigger as you increase the volume eventually the signal gets big enough it goes off the screen but I didnt see anything square. What scope settings do you recommend?
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Old 12th April 2011, 01:22 AM   #6
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Set the vertical amp so that the signal can't go off of the display.
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Old 12th April 2011, 01:23 AM   #7
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Do I need a load hooked to the terminals? I had no speakers hooked up during the scope output view.
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Old 12th April 2011, 01:26 AM   #8
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Only the repaired channel emmits the sound upon power on and off. The other channel does not do it.
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Old 12th April 2011, 01:26 AM   #9
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It's better to have a load. Sometimes, without a load the signal will remain clean even though there is a problem.
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Old 12th April 2011, 01:36 AM   #10
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Quote:
Originally Posted by Perry Babin View Post
It's better to have a load. Sometimes, without a load the signal will remain clean even though there is a problem.
I hooked up the speakers and turn the volume to 30 which is max. I cant get the clipping signal you desire. The signal is clean both channels. I am using a Rockford head unit, maybe because they deliver NO as in zero distortion in the signal even at max volume?

Last edited by seankane; 12th April 2011 at 01:36 AM. Reason: spelling
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