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Old 20th March 2012, 11:33 PM   #1
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Default Mmats D100HC low output.

I have a Mmats D100HC on my bench and it plays with gain set (on speaker terminals) 14v w/32hz sinewave and 23v w/100hz sinewave if I go anyhigher on the gain the audio is clipping (DC in speaker termnials about 3dcv).

I have a 15amp fuse and it doesn't pop it while playing, I checked the idle current and its below 5amps (only know that because it didn't pop a 5amp fuse untill signal was on the RCA's).

The amplifier is hooked up with two 10" woofers (4-ohm each, so total load 2-ohms). The amp is stable down to .67ohm, I dont believe the problem is a 2-ohm load I just expect less power, maybe around 400-500 for 2ohms.



*What I've done so far*
-Replaced a capacitor (C01) since it had leaked on the board. It was a 47uf 50V NP , I used a Xicon 47uf 50V NP axial capacitor.


Dont believe the 4080 chip is damaged because it plays but maybe it could be. This amplifier has 3 IC sockets (8pin-MIC4424CN ; 16pin-SG3525A ; 20pin-HIP4080AIP) so am guessing one of those if not all three may be damaged (why would they put IC sockets unless you intend to replace them in the future or upgrade/revisions).



Anyhelp is appreciated.
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Old 21st March 2012, 07:16 AM   #2
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The 8-pin driver and the 4080 are in sockets because they fail virtually 100% of the time when the transistors that they're driving fail.

Are you saying that you have a DC offset between the positive and negative speaker terminals of 3v?

What's the rail voltage?

What's the DC voltage on the speaker terminals with the black probe on the amp's ground terminal?
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Old 21st March 2012, 03:30 PM   #3
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Are you saying that you have a DC offset between the positive and negative speaker terminals of 3v?
Correct, only when I adjust the gain to get to normal playing volume (once ac voltage reaches 22v on a 100hz sinewave it starts to clip/distort pretty bad) so I put my dmm in DC and once it starts to clip/distort I read around 3dcv on the speaker terminals.

-This amplifier is about a 1200watt @ .67ohm ; 300-500watt @ 2ohm ; 100watt @ 4ohm



What's the rail voltage?
Am not too familiar with these class D amplifiers, can you tell me where I can check the rail ( I remember that on the class A/B amps is by the rectifiers/transformer but would it be the same on the Class D?) Would black probe go on ground or on the rectifier?



What's the DC voltage on the speaker terminals with the black probe on the amp's ground terminal?


I'll check in a few minutes and let you know, I'll do both with audio and without audio.
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Old 21st March 2012, 03:48 PM   #4
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Also the 47uf 100v NP cap that leaked was in between positive and negative speaker outputs (with series with a 2.2ohm 5watt resistor). Dont know what thats suppost to do.

I'll get you the readings, perry.
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Old 21st March 2012, 03:53 PM   #5
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Check the rail voltage on the rectifiers. It will probably only have positive rail voltage. Place the black probe on the amp's ground terminal.
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Old 21st March 2012, 05:03 PM   #6
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What's the rail voltage?

* 46.53dcv on the rectifiers with black probe on ground terminal. (only the middle leg of the rectifiers had voltage)*





What's the DC voltage on the speaker terminals with the black probe on the amp's ground terminal?

* 23.31dcv on the positive terminal and 23.34dvc on the negative terminal.*
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Old 21st March 2012, 05:43 PM   #7
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I know the DC voltage on the speaker terminals should read .001 (very low) but mine are extremley high.

I just checked the rail voltage on a crappy Bazooka El1500 and that sucker has 120v (I guess since its class A/B) and on the speaker terminal it read .0005dcv.
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Old 22nd March 2012, 10:45 AM   #8
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The DC between the terminals should be near 0v. The voltage referenced to ground should be 1/2 of the rail voltage.

Does the rail voltage drop when you test it as described in post #1?
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Old 22nd March 2012, 10:32 PM   #9
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Does the rail voltage drop when you test it as described in post #1?

** Yes sir it does, once it starts clipping the rail dips to 39.24dcV. **
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Old 23rd March 2012, 02:21 AM   #10
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Quote:
Originally Posted by jeanious2011 View Post
Does the rail voltage drop when you test it as described in post #1?

** Yes sir it does, once it starts clipping the rail dips to 39.24dcV. **

That may figure why I get 3.5dcV on the speaker terminals when it clips (+3.5 plus -3.5 = 7dcv which are missing in the rail voltatageonce it starts clipping??????
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