A little preface about the project: I want a rockin' system in my shop! LOL! Since I am somewhat of a 12v amp junkie, and I have a fairly robust power-supply (ASTRON RS70m), and I want to use active crossovers, it only makes sense for me to use 12v amps. Plus building this rig will be a really fun project.
A while back I picked up a few case-less M25's. I am a machinist, and I also like to machine parts for amps. So, I scooped up those M25's knowing I could do something with them. I was originally going to build a staggered 4-ch amp with them. Two of the amps pridged, and one stereo. In a tower arrangement. It would have fit well in the center console of my truck. Here was the mock-up:
But I ended up going a different direction in the truck, and kinda forgot about these guys. Now that I have had my shop open for about a year, and spend a ridiculous amount of time there, I would really enjoy a nice system. While I was shopping for 120v amps, and trying to figure out how I was going to accomplish an active crossover (on the cheap!) I remembered these guys, and my ASTRON! So I drug them back out.
That's when I got to thinking, "hmmm, I could really use more power". So I started hunting for a pair of M50's for subwoofer duty. Took a few weeks, But i managed to round a couple up (one is still en-route from overseas). And finally, I picked up an ALPINE CDA-9887 to use for a source. I figured a head-unit would be a good solution to a source, and processor all in one. And I am very familiar with the 9887. When one popped up super cheap, I snagged that too.
So, The plan for wicked shop tunes is set. ASTRON for 12v power, 9887 as a source, Phoenix Gold M-series for power! The only thing still in the air is speakers. I have three M25's, and two M50's. I am sure that I will run both M50's each bridged on a nice 12" sub in a ported enclosure. Then for the top end, I am undecided. I will either bridge two M25's, each on a midwoofer, and the third M25 will power tweeters. OR! I will simply bridge two M25's, each powering a nice full-range driver. I am really leaning towards the full-ranges for a few reasons. One, efficiency. There are some nice efficient drivers that will get plenty loud off 100watts, and still sound fantastic. And I really could care less about imaging. This whole rig will be parked on some pallet-racking in the back of the shop. And, I will already be pushing the limits of my available 70amps with just the M50's, let alone three added M25's. So, I will most likely just run the two M25's and full-range drivers.
I will fabricate a chassis for all this. It will be cool. But, I am getting ahead of myself a little bit there.
First things first. These OLD amps need some attention! So tonight I pulled the heat-sinks off one M25, and one M50. The sink needed to come off the M25 because I wanted to swap the sun faded sink on one of my boards out for another nice one that matches the rest I happen to have. And The sink needs to come off the M50 because I want to perform Eric's resistor mod. To get them up and away from the board. The board on this amp happens to be baked pretty good. It has not failed. But, definitely is a perfect candidate for the mod.
It is at this point that I would like to ask for some help if I could! First: I can't find a schematic for the M50, and I dont know how to read resistors. Can anybody tell me what the value of these guys is?
Can anybody confirm the values for the 4 dudes dead center of the above pic?
And then, while popping the transistors free from the sil-pads:
WTH? I have never seen this happen before! LOL. Do I need to replace these as a set? And, its obviously an IRFZ44. But, which variation should I order? I have found several!
And finally:
I am guessing I don't need to worry about this one? Is this just cosmetic? Or should It be replaced?
I am comprising a big ole' parts list, and any help on determining just what I need, would be greatly appreciated!
. There will be some hard-wiring going on when it goes back together.
