MXL 9000 capsule/resistor advice

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Enchilada

Well-known member
Joined
Aug 24, 2011
Messages
323
Location
Australia
Hi Guys,

I've been over at this really old thread and instead of reviving it, I figured I would start a new one.

http://www.groupdiy.com/index.php?topic=10077.0

I picked one an MXL 9000 used for $50 a couple of weeks ago. Tried it out and it was harsh! Popped in a NOS JAN GE 6072A and it really smoothed things out. Was still suffering from a ridiculous proximity effect though an the mic was basically unusable for vocals within six inches. Based on discussions in the aforementioned thread I replaced the stock transformer with a Cinemag CM-2480 (10:1 I think), removed C3 (9pf) and replaced the 33uF electrolytic cap at C6 with a 1uF polypropylene cap. This mic is now amazingly better! No overhyped proximity effect, sounds nice from any distance, plenty of gain, massive drop in self noise compared to stock.

Now here are my questions:

1.) Would it be worthwhile lowering the value of R7 from 6.2k to 2.2k to 2.7K? What effect would this have?

2.) Would it be worthwhile replacing the stock capsule for another? I have a Studio Projects C1 and an MXL V67G I would be able to swap capsules with if it would be considered much of an upgrade.

3.) Are there any other mods which come to mind e.g. Power Supply, Headbasket etc...

4.) Anybody know any good tube mic designs which could incorporate any of the capsules I have available to me and the Cinemag CM-2480 if I were to replace the PCB altogether?

Thanks!!!

Kris (the enchilada)
 
hi there, welcome!

As for changing the operating point, I don't see how it would benefit you. What are you trying to change by doing this?
The capsule is going to be the big game changer after the mods you've done already.

If you're looking to build another tube mic, check out the g7 project. I don't know if anyone is making pcbs yet (some are organizing a group buy?) but there is plenty of documentation on the project.
 
Thanks for the reply Rodney. As for changing the operation point, I don't know much about it to be honest. It was a recommendation in the thread I linked to and I was curious to see if there was any benefit.

Suppose I should do some more research on which capsules would best suit this circuit.

I checked out the G7 project, although I have a limited knowledge of electronics I am able to etch and solder my own PCB with no problems (I'm currently working on a MIDI drum controller  ;D). I saw they have a PCB transfer in pdf format, I may have to find a cheap donor mic and give it a go I think!
 
well, I'm not sure either, but I just read the first part of that thread, and if Gus recommended changing it to 2.2k-2.7k I'd take that and run with it. He's knows...things...

Couldn't hurt.

When I see a triode mic, I think c12 capsule, so I would go find a good version of that. on the low end of the food chain is the rk12, more in my budget. More expensive is a peluso CEK-12...too rich for my blood at the moment. Then there's the one everyone is talking about but I can't remember who makes it...

Or just a straight up AKG C12 capsule.

If you want the slightly darker sound, go for a k47 type, with center termination. My personal favorite for vocals.
 
Hey Kris,
  I've had one of these mics for a few years, and contributed to the thread you referenced. Bought mine @ the same price you paid. It had been abused a bit and I had to replace C3, which was causing some nasty noise. Tried it first without it, and found the sound to be a bit overhyped on the high end. Put a 5pf/5000v ceramic cap in there and liked the results. 10pf might be OK, too, just a bit darker. Seems like it should be a polypro like the one that was in there, but I'm not missing it, and I think the original polypro is underrated for the voltage in that spot.
  It now has a 5965 tube in it, which also sounds good. Original transformer sounds OK, but Cinemag would be better.
  Since you put the Cinemag in there, you can remove L1, L2, C21, and C22. Don't jumper the caps, but do jumper across where the inductors were.
  R7 is part of a filter network with C5. Gus knows his %^&!.
  The capsule change recommended by Rodney is the next step, but if you like the sound of the mic, why bother? Sounds like a succesful upgrade to me. It's the same capsule as you will find in your V67, some are OK, most are so-so. The SPC1 has a bit nicer capsule, made by 797. All I would do with that mic is maybe upgrade some caps, but I have a B1, and they used nicer caps in that than the MXL mics. My B1 has a mid-dip, but works on certain sources, so I leave it alone.
  I did a Royer 1 mod to a V67g, and it was a much improved mic, and I learned a lot. After a while, I switched the guts to a 2001 body and capsule, which is exactly the same circuit as the V67, but I guess the gold and green make it sound better :).
  Was tempted to put the Royer 1 circuit in a MXL 2003 to hear it with a 797 capsule, but I like my improved 2003 too much to mess with it. Probably my fave mic for my own vocals. Simple upgrade, too.
  On my Nady 1050, every electronic upgrade I do shows me how much I need to replace the capsule. Might be the same here. One day will try the capsules Rodney referenced, when "disposable income" becomes part of my vocabulary again. 
  Don't remove any head basket screen. Really...don't do it. Takes shielding away from the capsule.
  Did you remove C6A?
    If you wanna mess with the PS, maybe just replace the caps with higher quality/ higher temp-rated caps.
    My 9000 sounds really good at the moment, but haven't found it's special purpose yet. It's not for my voice, but like my Royer 2001, sounds great as a room or drum overhead mic. Weird circuit, which is why I like it. Same with the Nady. Kept the original CCDA circuit.
  Don't fall prey to "Mod Fever". Learn when to step back and enjoy the results. If you can print boards, make a G7 and put a proper capsule in it. THAT will blow you away.
 
I agree with tchgtr (teach guitar?) about not over-doing it.

I built a g7 with a 6SJ7, a radio shack power transformer for an OT, and a cheap chinese k67 capsule with only one skin (only using it for cardioid anyway).

I LOVE that mic. Use it constantly, and won't change a thing, except maybe the capsule in the not so near future.
 
Thanks tchgtr for the advice/feedback. I haven't removed C6A because embarrassingly, I couldn't find it  :-[.

I'm thinking I might try a 2.2k at R7, replace L1, L2, C21, and C22 with jumpers and puitting the 9pF cap back at c3 and see how that sounds. I'll have a look in the power supply too and see if there are any caps there I can replace with higher rated ones.

Gemini86, I looked into the cheapest C12 style capsule you suggested. Not a bad deal, I might go for it and see how it goes.
 
...and don't put larger value caps in the PS (in terms of uf that is, tho some folks might recommend this), but they should be better quality like Panasonic or Nichicon, and have a higher temp rating (like 105 degrees Celcius). It's not too important, but could possibly make it a bit less noisy. Eventually, all electros get old and weaker, so you could even wait a while.
You can leave C6a in there, it's kind of a hi freq bypass that aids the original electrolytic in there, but you might like it better without, if the mic is a bit shrill. Now that you have a polypro in there, it's not so important. Just look for a cap (maybe a blue film cap) wired in parallel with your 1uf polypro.
    Rodney-did you just do that G7 P2P? Sounds interesting, and may be the next project for me. Do you mind sharing which power transformer? I love that kinda DIY, and used donor mics are so inexpensive in these parts.
I do teach guitar sometimes, but that's not what it stands for... ;)
 
I did post a thread after I finished it, just search g7 6sj7 and you should find it. The output trans is a 120:24v with ct, you can wire it for either 5:1 or 10:1 with the CT on the secondary.  I chose 10:1. I didn't do p2p but I did hand draw the circuit onto the PCB.
 
tchgtr said:
...and don't put larger value caps in the PS (in terms of uf that is, tho some folks might recommend this), but they should be better quality like Panasonic or Nichicon, and have a higher temp rating (like 105 degrees Celcius). It's not too important, but could possibly make it a bit less noisy. Eventually, all electros get old and weaker, so you could even wait a while.
You can leave C6a in there, it's kind of a hi freq bypass that aids the original electrolytic in there, but you might like it better without, if the mic is a bit shrill. Now that you have a polypro in there, it's not so important. Just look for a cap (maybe a blue film cap) wired in parallel with your 1uf polypro.
    Rodney-did you just do that G7 P2P? Sounds interesting, and may be the next project for me. Do you mind sharing which power transformer? I love that kinda DIY, and used donor mics are so inexpensive in these parts.
I do teach guitar sometimes, but that's not what it stands for... ;)

OK, here's a recap EVERYTHING I've done to this mic so far:

Replaced the stock tube with a NOS JAN GE 6072A
Replaced the stock transformer with a Cinemag CM-2480
Replaced the 33uF electrolytic at C6 with a 1uF polypropylene
Replaced the 6K2 resistor at R7 with 2K2
Replaced L1 and L2 with jumpers
Removed C21 and C22 (actually, I couldn't get one of the wires out of C22 but as one of wires isn't connected I'm assuming this will be OK)

It sounds a lot better than it did stock but I still think I could tame the highs a little more.

Tchgtr, there is a blue capacitor under C3 which has no label on the PCB. I'll assume this is C6a. What you're saying is that to remove this cap may help tame the high end?

With regards to C3, could I put one of these 3-10pF trimmers in and adjust it to taste?
 
Enchilada said:
It sounds a lot better than it did stock but I still think I could tame the highs a little more.

Tchgtr, there is a blue capacitor under C3 which has no label on the PCB. I'll assume this is C6a. What you're saying is that to remove this cap may help tame the high end?

With regards to C3, could I put one of these 3-10pF trimmers in and adjust it to taste?

C6a was there to pass the highs that an electrolytic in the place of C6 would not pass. Now that you have a nice polypro there, it's not needed. It's labeled clearly on mine (now that the cap is gone), so just look for a .1uf cap that isn't C4 or C41, and is connected directly to the leads of C6. This may tame the high end a bit.

C3 acts as a high pass. The smaller the value, the more highs it passes. When I took it out completely, the mic was too shrill, but had a lot of output volume. I tried a 22pf, which made the mic nice and dark, but also reduced the output. You can try the trimmer, but I think a specific cap would be better.
 
Hey all,

Quick update for those keeping score. I've replaced the capsule with a Chinese C12 style. Haven't removed C6a or changed the value of C3 as yet although going off the highs I'm pretty sure I will.

Here's a sample of the mic, any input would be much appreciated :) http://soundcloud.com/kris-osullivan/mxl-9000-plate-reverb-test

Signal chain: MXL 9000 --> Tascam M-3700 --> M-Audio Delta 1010 --> Reaper --> Universal Audio 1176LN (UAD2)

I was actually testing a DIY plate reverb with this recording but I'm sure you'll be able to hear the mic to. The highs are still a little wild for my taste but the mic is MUCH warmer sounding than stock so I'm still happy. I'll now remove C6a and I'm pretty sure I've got some spare 22pF polystyrene caps so I may throw one of those in there for laughs.

One more note, the output of this mic is REALLY hot at this point. The recording is clearly clipping and the mic preamp in my console was at around 1/3 of the way.
 
Enchilada said:
Quick update for those keeping score. I've replaced the capsule with a Chinese C12 style.

Hey guys,

I know this is very old post but have a question.  I am making a lot of these upgrades to my MXL 9000 as my first test project to get comfortable etc. 

Question:  The C-12 style capsule I want to install has 4 wires (2 blue/2red) but the MXL 9000 capsule only has the two wires.  How did you approach this when modding your mic?
 
The C12 clone is a dual capsule, but the MXL 9000 is only a cardioid mic, "hearing" only from one side of the headbasket (whereas a C12 will "listen" out of both sides of the head basket, but only when it is in omni or figure 8 mode .
This means you must hook up only two of the wires from your new capsule, and you will be using only one side of the capsule. You must figure out which two wires connect one of the diaphragms on the capsule, which will hopefully be "listening" in the direction you want. If you get it wrong, just use the other two wires.

After reading my old responses to this, I would like to add that I replaced the original capsule in my 9000 with one I pulled from a M Audio Nova mic. It was one of the (IMHO) better-sounding capsules with the white plastic ring around the diaphragm, which I believe were made in the 797 factory. It was such a vast improvement over the original capsule, that I eventually bought another used 9000, and another used Nova, and did the same thing so I would have a stereo pair.
Absolutely fantastic for acoustic guitar.
One of the Nova bodies went to a Big Ugly Royer variation which combined the Royer mod with the multi-pattern options of the G7 mic, on which I used a C12 clone that I got from a group buy here many years ago.
It is now one of my favorite mics for my own voice. Love this forum.
 
tchgtr said:
The C12 clone is a dual capsule, but the MXL 9000 is only a cardioid mic, "hearing" only from one side of the headbasket (whereas a C12 will "listen" out of both sides of the head basket, but only when it is in omni or figure 8 mode .
This means you must hook up only two of the wires from your new capsule, and you will be using only one side of the capsule. You must figure out which two wires connect one of the diaphragms on the capsule, which will hopefully be "listening" in the direction you want. If you get it wrong, just use the other two wires.

After reading my old responses to this, I would like to add that I replaced the original capsule in my 9000 with one I pulled from a M Audio Nova mic. It was one of the (IMHO) better-sounding capsules with the white plastic ring around the diaphragm, which I believe were made in the 797 factory. It was such a vast improvement over the original capsule, that I eventually bought another used 9000, and another used Nova, and did the same thing so I would have a stereo pair.
Absolutely fantastic for acoustic guitar.
One of the Nova bodies went to a Big Ugly Royer variation which combined the Royer mod with the multi-pattern options of the G7 mic, on which I used a C12 clone that I got from a group buy here many years ago.
It is now one of my favorite mics for my own voice. Love this forum.

Awesome.  Thank you so much for the reply.  I'll send some updates to my mod for anyone interested.
 

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