I'm not sure where to start this one so this is the GroupDIY post that started it: (those guys are trouble, I tell you.) One thing to note is the schematic is apparently nowhere to be found in 2018, so this whole thing is based on text advice.
I got an MDX-1200 on ebay for pennies, and it came to me in apparently NOS condition. Including original packaging. However I later discovered that the bypass switches are both intermittent. Exactly 1 year later I decided to do the work. On a slow day that needed some activity.
The achilles heel of these cheap compressors (behringer, Alesis) if you go back through my posts is always the cheap switches. They just don't last. I've bought and sold a few of these kinds of boxes with the same problems. You simply can't rely on them. I may have to even eventually "Mod" this compressor with some regular toggle switches. For now I just don't touch them. (If you jam them enough times they work.) I could also recommend to not buy these. If you are in a busy studio.
Basically the plan, as usual, is to upgrade the op amps and some of the capacitors. I made an image list that I will post here:
All the stuff I got from Mouser. Here are the parts I ordered (I did also order some spare capacitors, so there's extra on this list than what was used.)
The job took about 4 hours with several breaks. That's FOUR HOURS I could have spent building my Serpent SB4000 Kit!!! Let's call it practice, I guess. The main thing is that I got it done and it worked on the first plug-in. Just testing my skills. I was careful not to destroy the pots when pulling off the knobs. Something that went wrong with my Composer and Alesis mods. I decided to de-solder the red and black wires to the front panel LED's so I could remove the front panel and freely work on the PCB. I had to re-solder them at the end of the work. (Pictured, sort of.)
I also learned a new technique of using desoldering braid. I place it across the 7 holes of the big op amps which are removed already, and gently roll the iron across the braid for about 30 seconds. You lift up the braid and most of the solder has been removed. Pretty cool. My new Hakko tweezers also really came in handy for desoldering the op amp legs after I cut off the op amps. Stick the iron on there, pull the leg part out with the tweezers. Then use the desoldering braid. Then put in your gold pin sockets, and finally your new op amps (after you have done your PSU bypassing with .100uF caps.)
This was also my first time of bypassing the op amps. You can see that I soldered some small ceramic capacitors to the bottom of the PCB. What you do is find the + and - voltage pins on each op amp IC, mark them with a black dot (marker), find the nearest ground solder pad with a multimeter (in continuity beep mode) circle that. Then put 2 caps from + and - to ground. Apparently this is an oversight in shitty designs like these that should have been there if it were a good design in the first place. My caps were small enough (MLCC) to fit under the board. It was kind of fun and I'm glad I learned a new technique. If you try to use certain high slew rate op amps in an un-bypassed circuit sometimes they will oscillate and possibly even destroy themselves. This happened to me with one of my Symetrix 501 mods from years ago. That poor bastard finally got sold on Reverb.com to someone with a better heart than me.
Sound is very high-mid forward and tight, with good bass extension. It's a pretty aggressive punchy sounding compressor. There is some distortion or clicking noises on the attack of bass notes. Knob positions don't seem to help that much. On bass synth anything below 10ms on the attack knob results in ugly distortion. I wonder if I need to disable the gates or "enhancer" somehow. This is making the compressor questionable for studio use. HOWEVER it sounds pretty killer on snare drum. Beats my plugin chain. I think a tiny bit of crunch would just blend in with the snare wires, I'm not sure I can even hear it. The Midas 512 is also working great on snare drum EQ. So this goes next to my Composer mod as another "dirty compressor" which is once in a while useful. I used it on a dirty synth line also and it made it stand out in the mix.
I can't recommend this project based on time spent and shoddy switches. But if you are the tinkering and learning type it could be worth doing, if you already seem to have and MDX-1200 on hand. Total project cost including the compressor was about $75 so yeah this is pretty dirt cheap, even after the mods. Comparing value, a DBX 560A for under $150 or so would be a much smarter investment. That's a tool that's going to be a lot more useful in any given session, and probably built a lot better as well. The bottom line is these Behringer compressors are sort of a novelty. People just mod them because they are so cheap, and the circuit board is easy to work on, once you get it out of the case. These kinds of basic mods don't really turn them into "pro gear" it's a bit of putting a Hemi into a Pinto kind of result. If I had to pick one, I'd say the MDX2100 Composer is probably going to be your better bet than this one. The Composer just turned out better, and I think the earlier generations of these boxes had slightly better switches.
I am even told that the VCA in these are very similar to the ones in SSL compressors, if not even slightly better than the SSL VCA. Not that they are going to sound the same because of that, but that this compressor might be actually useful to me now. It's sitting in a sad and happy place in my rack with my Alesis 3630 and Behringer Composer from previous attempts. Sort of like how Sylvia Massey has her broken Army Man Compressor. It's 3 rack spaces of semi-working upgraded stuff that does sound pretty cool, but that could never really be sold or recreated. It's all in good fun, and a good deed never goes unpunished.