MXL 990 Modifications

July 16, 2009, 4:31 p.m.

MXL 990  While researching on the internet, I came across a lot of examples of people suggesting modifications to cheap condensor circuits (like the 990) to remove some of the limitations of the cheaper circuits and headbaskets.  While a lot of people said they got good results from removing the internal two mesh grilles and changing some capacitors, I didn't find a whole lot in the way of instruction, so hopefully this might help assist someone considering these mods. First, removing the two internal mesh layers was pretty easy, but scary and time consuming.  There are two halves inside, so I would recommend starting with one side, pulling the bottom edge up, then continuing to the rest.  Once one half is off, It is easier to start at the top on the second half.  Basically just get in there with some needlenose pliers and make sure you're just taking off the bottom two layers.

Next, I replaced capacitors C3 and C4 (both clearly labelled on the circuit board) with two .22uF poly film capacitors from RadioShack.  If you're pretty familiar with soldering, this was a very easy task.  Supposedly the circuit for the 990 and the mxl 603 pencil condensor are the same so information for the 603 (widely available, just search google) should also work for the MXL 990.  After doing all this modification, I wanted to compare the first mic I worked on, with my other, still stock, 990.  I recorded both through a DIGI 003 set on the same gain with no extra post-processing.  I recorded both at the same time, without letting myself know which mic went to which input, sort of a blind test.  To my suprise there was actually a pretty big difference.  The Modified sound was a lot hotter and had more high end.  In comparison, I thought the stock 990 sounded a little muffled.  I liked it enough that I performed the same modification on my stock 990 also.

Stock 990


Modified 990


Headbasket with first half of internal mesh removed, second half started 






  • I didn't normalize the clips, I kind of wanted to highlight the volume difference that just replacing the caps and removing the windscreen had at the same gain setting on the preamp. You are right though, samples with adjusted volume would give a much more accurate A/B. If I can find the time, I'll do that. Thanks for the suggestion on that and the other mod tip!
    jordancolburn - Oct. 10, 2012, 5:13 a.m.
  • Thanks. Also, some people are referring to 3 layers of mesh. I only have two in mine. I'm guessing that I start from the inside. I might try De-soldering otherwise it will be almost impossible to remove. Thanks for the attention and tips. My 990 with the RK-47 is my go to microphone at the moment.
    David Griffis - May 19, 2014, 6:18 a.m.
  • Not sure, It's been a long time, I'll open them up and check for you soon. And the mesh had a few two solder points, but I was able to use a pair of pliers to get it all out.
    jordancolburn - May 16, 2014, 9:35 a.m.
  • The .22uF poly film capacitors from RadioShack are enormous. Do you mean .022uF? Also, the mesh is soldered in. You can't just pull it out?
    David - May 16, 2014, 9:23 a.m.
  • I found that changing the values of C3 & C4 to 1mf, it helps with the lows. I also found that replacing all the ceramic caps with mylar caps really helped with linearity. The mic now sounds smoother and has that high end sound. The single best cap to replace is the C13 which is located on the 990's circuit board on the other side. Really helped with the 990's ability to sound so good! Other mods I did was get the K47 capsule from Microphone parts. That really made the MXL990 sound like a high end mic. With changing the caps and the cartridge, you will have a mic that can compete with some of the best at a price that can't be beat.
    Steve from Ohio - Jan. 6, 2014, 10:47 a.m.
  • Cool, glad you got it! I was going to go home and try it after work and let you know (I haven't messed with the insides of these mics in quite a while). Let me know how the mod goes for you.
    jordancolburn - Feb. 8, 2013, 11:28 a.m.
  • D'oh! I'm an idgit. Two screws. :)
    FarrisGoldstein (@FarrisGoldstein) - Feb. 8, 2013, 11:21 a.m.
  • More specifically, how did you pull the circuit/capsule assembly out of the headbasket? Unscrewing the sheath is easy, but now I'm left with the circuit/capsule wedged firmly inside the headbasket, with no obvious way to loosen it.
    FarrisGoldstein (@FarrisGoldstein) - Feb. 8, 2013, 7:05 a.m.
  • Hi there, I was just wondering how exactly you removed the headbasket. Must I also remove circuit?
    Glenn - Oct. 14, 2012, 8:22 a.m.
  • Hey, nice clips. Just curious, but did you normalize them? That way, it should eliminate the possibility that the modified clip is simply louder--which will almost always sound better to your ears. You can also replace the gate cap on the back side of the circuit board with a Styroflex polystyrene cap, too.
    Jon - July 19, 2012, 12:44 p.m.
  • If I remember correctly, I just unscrewed the the top portion on the mic and used a pair of needlenose pliers to remove the finer mesh, it's soldered in our something, so it's a lot of pulling and twisting, but after the first couple edges, it comes out easily enough. Be careful not to pull the outer mesh and damage the outside of the mic enclosure.
    jordancolburn - Oct. 18, 2012, 4:29 a.m.
  • This is great! Thank you so much for posting this! The sound clips really make this for me.
    Jessicaannewallace - Aug. 6, 2012, 9:20 a.m.
  • Gotcha! - Oh and thanks for the sound clips - they are greatly appreciated. -- Mike
    Guitar Builder - Feb. 3, 2012, 2:19 p.m.
  • Thanks for the feedback! Glad to know it helped someone. I honestly wasn't sure it would make a difference, but it really did! Now don't expect it to sound like a Neumann or anything, but I believe it really helped.
    jordancolburn - Feb. 3, 2012, 2:17 p.m.
  • I just bought a MXL-990 and I love it - for the price. However begin someone that has to tinker, I found your site. I am definetly tearing this mic apart and replacing the two caps you mention - Thanks for this post!
    Guitar Builder - Feb. 3, 2012, 2 p.m.
  • awesome.
    mike - Dec. 7, 2011, 1:19 a.m.
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