MXL 990, 991 and Oktava 319 Mods

[Chuck]

They looked like this before the mod:

[jbell]

These look similar to the Avantone CK1.  Are they the same mic?

They looked like this before the mod:

[Chuck]

They all start out as the same microphone, using basically the same circuit and the same capsule. Avantone may have better parts or QC. I have not opened up an Avantone.

[raymonda]

I did get the capsules modified. I touched them up with some Nickel Metallic (Krylon) spray paint.

What method did you use to sand them down?

[Chuck]

I hand sanded the front chamber off with 80 - 220 grit sand paper.
Then, I wound some gaffers tape around the sanding attachment on my dremel. I wound enough so that I could slip the capsule housing over it with the capsule being tightly secured. Then I checked and adjusted the run-out until it was pretty even all around.

I turned on the dremel and ran it against increasingly finer sand paper until I got the thickness and chamfer that I wanted. I finished by running it against some ScotchBrite. I measured everything and proceeded with the next one. It took 3 hours total.

[Chuck]

Hey Ray, do you know if these caps with fit on the MXL603/CAD GXL1200 bodies? Do they use the same diaphragm?

http://cgi.ebay.com/New-Mic-Hypercardioid-Capsules-MXL-CAD-Apex-45-/290467075180?pt=LH_DefaultDomain_0&hash=item43a12fd46c#ht_2088wt_906

http://cgi.ebay.com/New-Condenser-Mic-Omni-Capsules-MXL-CAD-Apex-43-/290467075171?pt=LH_DefaultDomain_0&hash=item43a12fd463#ht_2088wt_906

http://cgi.ebay.com/Condenser-Mic-Cardioid-Capsules-MXL-CAD-Apex-44-/290467075164?pt=LH_DefaultDomain_0&hash=item43a12fd45c#ht_2088wt_906

They are different than the typical capsule that came with these mics, as the vents are actually on the capsules. They're cheap too!



edit to add:
So far, his is one of the more satisfying recording gear mods I've done. It's so cool to be able to take the capsules apart and see exactly what the components are. If those eBay capsules will work, I'll have a pretty good pair of microphones with omni, cardioid and hyper-cardioid capsules for well under $200!

I've read everything I can get my hands on about these mics and have come to the conclusion that that are worth the work to mod.

[raymonda]

These don't look to be the right match for the MXL's and are not the same ones I bought off e-bay a while back. Wait until the others come back up on ebay.

[Chuck]

I finished moding my CAD GXL1200 microphones today.
I took some pictures.
The first picture is the stock internals. The rest of the pictures are of the finished mics.

The next thing is to take them out and use them.

[jbell]

Nice!  They look good

[illconditioned]

^^ nice work.


Any benefit to replacing the 1G resistors?  I don't know if they introduce noise or not, but I'm curious.


Also, can you tell me something about the capsule?  Electret or externally polarized?  Does it have the Neumann-look front, a brass plate with regular pattern of holes in front of the capsule?


  Richard

[Chuck]

Richard, I have taken apart the capsule. It's a gold sputtered diaphragm, a couple of spacers then the back-plate, venting holes and the center connector. The front does not have a plate with holes in front like the Neumanns. There was an elaborate grill on the front of the mic, but it's recommended to remove that, so I did. I put a 3/4" stainless steel screen in front to replace it.

Here's a little bit about it:

http://recordinghacks.com/microphones/MXL/603S

There are photos on line showing the disassembled capsules, but I'm having trouble find them online now. It's my understanding that it's a true condenser.

The capsule gets a lot of praise, that's why I started messing around with this mic. I haven't recorded anything loud with it yet.

I do not have a source for 1G or bigger resistors, so I didn't change them or the stock transistors.


Edit to add photo of dissected capsule.

[raymonda]

Nice work!!!!!!!!!!

[illconditioned]

^^^ Nice!  Thanks for the tech details.


  Richard

[kirk97132]

Chuck...first off, nice work!  So I see you had replaced a lot of stuff.  And I am wondering about a lot of things.  Should I ask here or would you rather take it to PM's or e-mail?  Thanks, Kirk

[Chuck]

Chuck...first off, nice work!  So I see you had replaced a lot of stuff.  And I am wondering about a lot of things.  Should I ask here or would you rather take it to PM's or e-mail?  Thanks, Kirk

Either way. But, keep in mind, I just followed instructions others have posted in various DIY forums. I didn't re-design anything. I can follow a schematic to stuff a circuit board, but I really can't design/re-design a circuit.

I started testing the moded mics this morning, while watching the Broncos lose to SF.

One of the bodies has 4-6dB less gain than the other and has a slightly different self noise sound. There is a 4v difference in the voltage getting to the capsules from the bodies. I have to admit that I don't have much experience working on transistor circuits. Op-amps I know pretty well, but transistors and biasing is not something I have done before. If biasing is even the problem

I replaced most of the resistors (hand matched values between mics) and capacitors, but left the main transistor 2SK170BL biasing resistors alone. I also didn't change any of the transistors.