MXL 991 Capsule Mod?????

mabell313 said:

Paul678 said:

mabell313 said:

Good stuff! Now I am sure not to screw it up! Thank you Paul. Very informative. I have been searching 603 capsule mods to no avail. Well, nothing clearly stating what to do. CAD 1200 search did the trick!  1000~4700pf is a good range for the caps you added. The caps are absent on the Chinese SDC's but are usually present on the LDC or the SDC that look like a LDC. THe caps go across R30 & R40 on the MXL 603 schematic which is the same as any of the other Chinese SDC's. I hope this is clear to you as it is early and  am nursing a pretty nasty hangover. Mmm, German beer.........

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    Well, just as a disclaimer, no matter how informed you may be, you can always STILL screw
a mic up if you are not careful!  The diaphragm is delicate, and you can easily lose the two plastic
spacer rings if you breathe too hard!  Also, it's VERY easy to leave dust or tiny particles of dirt
between the diaphragm and the back plate (you'll see the mylar get deformed).  In fact, I had to
disassemble and re-assemble 3 times before the mylar was clean and flat.

    Yes, you can put the caps in parallel with R30 and R40, but since they are virtually in series, you
can also simply use one cap of 1/2 the value, across both resistors (across the two bases of Q30 and Q40).

    It's amazing to tone-form a microphone!  It's almost like modifying an instrument!

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Indeed! Even if I screw the capsules up too bad the mics are dirt cheap. If I break it I'll just replace it. Don't you mean double(x2) the capacitance?

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  No, you are thinking two resistors in series.

  Two capacitors in series is like two parallel resistors:  if they are the same value, the equivalent
is 1/2 the value of one cap.

  Let us know how your mod goes...... 

Duh! Sorry, I realized that when I looked at the schematic this morning. You said you had tried a 47n and it was too much. What would be a good start? Maybe 2.2n? I will indeed post pictures of my progress, good or bad.

mabell313 said:

Duh! Sorry, I realized that when I looked at the schematic this morning. You said you had tried a 47n and it was too much. What would be a good start? Maybe 2.2n? I will indeed post pictures of my progress, good or bad.

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I'd start at 22nF, and move down if you want to get more high end back.

Upon re-listening to my recordings, I've decided to keep 47nF for the time being.  This
goes to show how much sibilance these capsules have, or at least my particular unit.

Of course, it will depend on your taste, and what you plan to mic it with.  Perhaps
you would like more high end if you were to mic cymbals, for example.

I'd also like to mention the MXL SP-1 uses the exact same capsule, and could
benefit from the same mod, if you would like to try to keep the stock capsule,
which would obviously save you some cash.  I would also leave off the large
brass ring the SP-1 uses, and I would also leave off the screen, leaving the
diaphragm open, because it will be protected by the headbasket mesh
anyways.    This should give it a truly open, un-hyped sound.