Mmats D100HC low output.

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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.
 
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?
 
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.
 
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.*
 
How do you know it's clipping without a scope?

I've used more advanced scopes but the Tek 465B is my favorite. I recommend buying a 465B if you can find a good one from a reputable seller (preferably with a warranty). If you can't find one, the 2200 series Tek scopes are nice. If you can spend a bit more, I'd suggest the BK Precision 2120B. You can buy them for just under $400. That's new with a 2 year warranty.
BK Precision 2120B, 30 MHz Dual-Trace Oscilloscope, B+K Precision 2120-B - at Test Equipment Depot

The first scope I purchased was a B&K. That was at least 25 years ago and it was old when I got it. It still works. The only thing that ever failed on it was an op-amp.
 
Dont know if its actually clipping, I assume because once it starts to distort I measure 3dcv on the speaker terminals but near 0 when amp is playing fine/low volume. Once it starts to distort (when I raise the gain to a certain point) and I have to bring the gain down just to cut the distortion. I never had another amp do this thats why I assumed it was clipping.

I am not a basshead and I dont use the gain as a volume (like bassheads would, lol) I know how to set gains using ohm's law, fluke 111 and a sinewave.

I'll look into buying a scope pretty soon so if I find one and have questions I'll be sure to let you know.
 
It's important to know if it's actually clipping. The distortion could be produced before the IC. It would also be good to see the square wave on the outputs.

If the rail voltage is not dropping too far, the two power supply ICs are probably OK. Without seeing the waveforms on the outputs, there's no way to determine if the IC is defective or not.

If you order ICs, order sockets also.
 
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