MMATS DHCX2200.05 Issue

mbates14

Member
2002-06-02 2:14 am
non
the outputs were totally blown up, but the power supply was fine.

So i replaced all the ouputs, and changed the HIP4080.

It powers up, but it just ticks. hear the ticking in the speaker. No sound. If i turn the gain up, it starts to sound like running/revving engine and eventually the amplifier actually "barks" through the speaker and shuts off. And starts ticking again.

I have no idea. where to look now. Maybe the ramp oscillator? any ideas?
 

mbates14

Member
2002-06-02 2:14 am
non
Well this thing blew itself up in my face again trying to find the fault. lol. So I gotta order all new FETs and 4080 again. AWESOME....

looks like im going to shotgun it and replace the 3525, and all the op-amps as well just to make sure.

I noticed the white noise/motorboating sound with ticking/phasor noise goes totally away if i heat the op-amp area with a heatgun. But ALL sound goes away. no audio.

BTW theres no audio or any presence of audio during the "freaking out" of the amplifier. Also the gain affects it. I can remove RCAs, and just turn the gain up and itll go into that freakout mode. If i turn the gain all the way to 0, it just ticks with an audiable pop-pop-pop-pop from the speaker.

Both the inverting and non-inverting input of the SG3525 are at 5V. The power supply will burst with gate drive for a short duration before going flat, every time it ticks. Its in sync with the output devices as well. For whatever reason, the amplifier output stage will not run. Fault LED is OFF. Power LED is on.

I might shotgun the caps too. I dont know yet. The output filters appear fine, bending/twisting the inductors make no change.

Pin 6 of the HIP4080 had a nice stable sawtooth wave on it. Pin 7 had a low level state, that was jumping around during the ticking. When the amplifier would go into its freak out mode, this pin contained a totally erratic oscillation waveform that was all over the map.

I looked at the 3710, its a nice transistor, also cheaper. BUT it gains more current at the cost of voltage. i noticed its 50v less than the 3415 counterpart.
 
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mbates14

Member
2002-06-02 2:14 am
non
Makes sense. Im thinking in terms of usage in other amplifiers. Just deciding to see if i wanna stock those instead of the 3415. Because right now, I stock TIP35/36, 3205, 3415, and P064s regularly.

Pertaining to the MMATS issue, I think it might be in the analog section. Having a nice sawtooth in the + input of the HIP4080's comparator, and having something indeterminate in the negative input means the "sound" i hear is real sound but coming from the audio preamp section.
 
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MatthewS

Member
2008-02-22 9:19 pm
IIRC MMATS had nothing but issues with the lines built around that driver IC. Then again, everyone that used it kinda sorta had nothing but issues.. LOL. I had a few here and hated them. I ended up making some modifications to one of them and I found out the hard way I got a bad batch of HIP4080's as well. In fact, don't rule that out as they had similar results to your issues. Also the output gates need to be as close to original as possible and that presents some issues as even matching the original part numbers just doesn't guarantee it. The whole damn idea was a mess and an amplifier should have never been designed around it. I looked over the application notes on that chip and it would seem that some manufacturers flat out ignored them at times. Good luck with that thing.
 

mbates14

Member
2002-06-02 2:14 am
non
Strange though, I never had issues with any other HIP based amplifier. It must be this design. And not so strangely, I cant find a schematic on this thing either. Anyway, I appreciate the help. Thinking i might disconnect the analog stage and trace it a block at a time.

EDIT: Original FETs are P80N06 i think. which is 3660pf gate capacitance, the 3415 is 2600pf.

Edit 2: I had noticed depending on the manufacturer of the P80N06, it varies alot...
 
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Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
You won't have clean audio going into the 4080. The op-amp used for feedback compensation constantly modifies its output to make the output at the speaker terminals clean.

The 3710Z is the only transistor that I've found that works properly in virtually all of the 4080 amps. There are likely to be better FETs on the horizon but I haven't found any yet.

When the output FETs are incompatible, it can cause all sorts of problems. If you have an amp that you want to use a particular FETs in but you're having problems, install a full set of 3710Zs. If the amp works flawlessly, you know that the problem is almost certainly the other FETs. If it doesn't work with the 3710Zs, you need to do some more troubleshooting. If you find that there is a problem and you can get it to work with the 3710Zs after you repair that fault, then you can go back to the other FETs to see if they'll work.
 

mbates14

Member
2002-06-02 2:14 am
non
Well i gotta order all new FETs and a new 4080 anyway, so i might as well grab some 3710s. Plus they are cheaper, i order all my stuff from digikey. I also noticed this amp does not use split-rail system either. And none of the op-amps are split rail. They are +10V (thats what i read) and GND.
 
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Worked on the MMATs a little bit more today, one thign I had noticed was if i power the amplifier without the remote, it FAULT light will light up and thats it. thats hooking power to it without remote.

If i let it drain off of course, and hook remote up and power it up again itll power on and do its usual thing. However if i unhook remote while its powered up, it will power off but the power LED will stay illuminated.

So maybe there is bad comparators somewhere.
 

mbates14

Member
2002-06-02 2:14 am
non
I got the new outputs in, Same issue. So, i traced the feedback wires to the LM837. I replaced that, and bingo I got my sound back.

However it was clipping/distorted when turned up a little bit, and the leds/remote were still acting weird. So after chasing my tail a bit. I found Q20 blown, and Q21 blown as well.

Replaced those (appear to be in remote circuit) and now the amp works perfectly. Perfect sound, and the amp isnt acting weird anymore.

Man... talk about chasing ghosts. hehe.
 
The audio going into the 4080 will change with the load. With no load, it may appear to be clean but when loaded, it may change so much that it doesn't look anything like the output signal.

The input of the 4080 has to be biased to approximately 1/2 of the supply voltage. The supply is approximately 12v so the input to both the inverting and non-inverting is biased to about 6v.

Compensation is completely different. The feedback compensation/servo circuit compares the input signal to the output signal and makes instantaneous corrections to ensure that the output signal is as it should be.
 

mbates14

Member
2002-06-02 2:14 am
non
This amplifier has a mind of its own. It was fine on the bench. So i moved it to the other bench to do a better load testing. Started that popping/crackling/bottoming out sound (Class-D typical distortion). when turned up a little bit. So what the heck.

Powered it all down, let it set. Powered it up and it was fine. no more distortion. I was able to peak it at 35V RMS at a 1ohm load and it never got even warm. Thats about 1200 watts or so. Anything higher than that, the power transformer would ring bloody murder.

So, who knows...
 

MatthewS

Member
2008-02-22 9:19 pm
Told ya.. Freakin voodoo amps.. If the damn DHC series didn't get everyone hooked..

They're a good company, doing good things in the US. That said, I had a phone convo with someone down there I cannot name, and even he admits those amps had alllllll sorts of strange issues. Anything in the series with that damn chip. I tell people to send 'em to MMATS when they need work, let them deal with it. I have seen revisions soldered in on some, so they may make some changes when they go back. I recall Rockford did this with one of their BD's they weren't happy with (or maybe two).

Good luck never seeing that thing again.. LOL.
 

mbates14

Member
2002-06-02 2:14 am
non
It would be nice to know how to revise the circuit to make it work better, but i dont know or understand the original design to begin with to do that.

Anyway, these ICs were meant to drive motor controllers, NOT class D amplifiers but i guess it works. lol. I have seen these ICs used in quite a few compressor inverters and a dozen servo drives. None of the higher end stuff though like allen bradley.

However this amplifier does beat the trunk off the car when loaded good. It just has that ever so low "bottoming out" type of distortion. (hardly audible, but present).
 
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