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FoundationSound

MXL 991 mod
« on: March 15, 2006, 11:58:00 PM »
I own a studio in Denton, TX.  A friend of mine who wanted to do some home recording bought 2 MXL 990/991 kits the other day and asked me to see what they sounded good on in the studio.  I immediately said under my breath... "nothing".  

However, the large diaphragm sounded pretty good on the toms believe it or not (at least way better than a 57, which doesn't say much).  I tried the 991 (small diaphragm) on hi-hat and guitar cabs and was less than impressed.  During the course of putting the mics to the test the 990's got a little banged up and I felt obligated to purchase 2 new mic packs for my friend.  

Now, I'm stuck with them.  I thought about e-baying them but the 990's sound pretty decent on toms so I might keep them around for drummer's who "aren't so accurate".   The 991's I'm not so sure what to do with.  Should I e-bay them?  

I was thinking about using the mic housing and the diaphragm and converting them into something else.  I found some old schematics on the Gyraf site the other day (http://www.gyraf.dk/schematics/schematics.html) and was thinking about the Neumann KM83's...  or maybe some of the AKG's.  I was just thinking about ditching the circuit board and printing a new one and throwing it in there.

Any suggestions?


northsiderap

Suggestions
« Reply #1 on: March 16, 2006, 12:03:31 AM »
I've noticed that these small diaphragm China capsules really open up with a good circuit behind them.

Are the 991s electret? I'm guessing they are.

Try the 'Alice' mic for electrets, or any high quality FET impedance converter circuit followed by a high-quality step-down transformer will work nicely.

I've been working on SDC circuits a bit, and it seems a DC converter to step up the polarization voltage a little bit helps too.
***NorthSideRap.com***

FoundationSound

MXL 991 mod
« Reply #2 on: March 16, 2006, 12:18:24 AM »
Can you point me in the right direction of where I can learn more about this kind of thing?  I can solder like a mad man but I'm really not too keen on a lot of things.  I've built some pretty complicated kits before (Neve 1272's) and I'm still working on a Gyraf G7 tube mic, but I've never designed anything before or worked directly from the the schematics alone.  Electret mics are just simple condenser mics right?  Here's the 991 (http://www.mxlmics.com/condencer_mic/900_Series/MXL991/mxl991.htm).  How do I know if it is one or not?  

Is it unreasonable to work off the Neumann KM84 circuit?  (http://www.gyraf.dk/schematics/Neumann_KM83-84-85.GIF)

Also, I found the Alice mic, where did he get the end-cap from?  I'm building a G7, what's the best way to cap it off at the boottm?  Any suggestions on that?

Marik

MXL 991 mod
« Reply #3 on: March 16, 2006, 12:28:42 AM »
Both of them are the same microphone in different clothes. Yup, the 990 although looks like a LD, in reality has exactly the same small capsule as 991, and exactly the same electronics. The difference in sound is due to different acoustical and grill construction.

991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones

pucho812

MXL 991 mod
« Reply #4 on: March 16, 2006, 12:36:21 AM »
Quote from: "FoundationSound"


Also, I found the Alice mic, where did he get the end-cap from?  I'm building a G7, what's the best way to cap it off at the boottm?  Any suggestions on that?


The end cap?  you mean the XLR connector? that is a switchcraft connector that is in their current line. The Male version is about 31 Milimeters in diameter.
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.

alk509

MXL 991 mod
« Reply #5 on: March 16, 2006, 12:41:56 AM »
Quote from: "FoundationSound"
I'm building a G7, what's the best way to cap it off at the boottm?






Peace,
Al.

Lest laziness get the best of you!

FoundationSound

MXL 991 mod
« Reply #6 on: March 16, 2006, 02:05:49 AM »
Al, yes!  Did you have that custom machined or can I find something like that already made?  Or do they sell something that looks halfway decent at ACE hardware where I bought the 2" copper tubing?  How much is too much to have something like that machined?

dayvel

MXL 991 mod
« Reply #7 on: March 16, 2006, 02:44:28 AM »
I'm not sure about ACE, (especially the small ones) but my hardware store has end caps in the same section as the copper pipe.

alk509

MXL 991 mod
« Reply #8 on: March 16, 2006, 08:26:27 AM »
Those end caps were custom-made for me by emachineshop. I designed them using their free CAD software. They were EX-PEN-SIVE, though...

Also, they're meant to fit true-2" brass railing tubing (1.9" inner diameter). 2" copper tubing is actually wider than 2", so these wouldn't fit. They sell copper end caps at the hardware store that go outside the copper pipe. They're ugly, but they'll do the job for a lot less money.

Peace,
Al.

Lest laziness get the best of you!

pucho812

MXL 991 mod
« Reply #9 on: March 16, 2006, 11:10:10 AM »
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.


Svart

MXL 991 mod
« Reply #10 on: March 16, 2006, 11:24:19 AM »
are they the same capsule?  I'm thinking the 990/991 was the transsound capsule right?
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

Gus

MXL 991 mod
« Reply #11 on: March 16, 2006, 01:00:48 PM »
I have not worked on a 990 or 991 but the picture I saw makes me think it is a variation of the 603 (china variation/version of a cmc5 schoeps circuit)

I don't like most SD with a baffle ring side addressed looks like a LD microphones.  The ATs are a different story.

Easy to upgrade, use the search and the Meta

You will be limited by the capsule more than anything else if you mod them.

  I had a pair of early 603s I modded(I lent them to a friend and never got them back)  I think something changed in the 603 capsules from the early ones to the newer ones.  

The Nady cm40? is kind of like the 603 without the input pot

Marik

MXL 991 mod
« Reply #12 on: March 16, 2006, 02:24:06 PM »
Quote from: "pucho812"
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?


When working on them I was holding in my hands both together at the same time. I could not find any differences. No idea how the Schoeps circuit in the same body from the same factory on the same PCB with the same capsule could give different measurements :shock: .
Maybe they were measured on a different day...  :wink:

As I stated earlier, I traced the MXL990 schematics and it is MXL603 on a different PCB.
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones

pucho812

MXL 991 mod
« Reply #13 on: March 16, 2006, 03:50:09 PM »
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?


When working on them I was holding in my hands both together at the same time. I could not find any differences. No idea how the Schoeps circuit in the same body from the same factory on the same PCB with the same capsule could give different measurements :shock: .
Maybe they were measured on a different day...  :wink:

As I stated earlier, I traced the MXL990 schematics and it is MXL603 on a different PCB.


Marik,
That is good to know as one can get a MXL 900 pack(a 990 + 991) at banjo center for the price of a 603. But makes me go Human error on the testing or they fudging their numbers to make it seem like two differnt mics? As per the mic data sheets there are differences ... I dunno I am so confused now :wink:
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.

Marik

MXL 991 mod
« Reply #14 on: March 16, 2006, 04:35:48 PM »
Quote from: "pucho812"
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?


When working on them I was holding in my hands both together at the same time. I could not find any differences. No idea how the Schoeps circuit in the same body from the same factory on the same PCB with the same capsule could give different measurements :shock: .
Maybe they were measured on a different day...  :wink:

As I stated earlier, I traced the MXL990 schematics and it is MXL603 on a different PCB.


Marik,
That is good to know as one can get a MXL 900 pack(a 990 + 991) at banjo center for the price of a 603. But makes me go Human error on the testing or they fudging their numbers to make it seem like two differnt mics? As per the mic data sheets there are differences ... I dunno I am so confused now :wink:


My speculation is that because of price match issues, nice folks from GC could not sell 603 cheap enough, so the MXL made the 991 and slightly "changed" curves, to avoid suspicions.
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones

northsiderap

electret?
« Reply #15 on: March 16, 2006, 05:19:42 PM »
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?


When working on them I was holding in my hands both together at the same time. I could not find any differences. No idea how the Schoeps circuit in the same body from the same factory on the same PCB with the same capsule could give different measurements :shock: .
Maybe they were measured on a different day...  :wink:

As I stated earlier, I traced the MXL990 schematics and it is MXL603 on a different PCB.


Marik,
That is good to know as one can get a MXL 900 pack(a 990 + 991) at banjo center for the price of a 603. But makes me go Human error on the testing or they fudging their numbers to make it seem like two differnt mics? As per the mic data sheets there are differences ... I dunno I am so confused now :wink:


My speculation is that because of price match issues, nice folks from GC could not sell 603 cheap enough, so the MXL made the 991 and slightly "changed" curves, to avoid suspicions.


Are you sure this isn't an electret? That might explain both the price and response changes.
***NorthSideRap.com***

CJ

Re: electret?
« Reply #16 on: March 16, 2006, 06:06:32 PM »
Quote from: "northsiderap"
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"
Quote from: "pucho812"
Quote from: "Marik"


991 is rebranded for GC MXL603. Make a search here. You will find looong thread on its mods.


The data sheets are slightly different between the 2. the 991 has an input impedence of 110ohms while the 603 is 150 ohms. The frequency responce chart is also different. Is that due to construction or is there actually a slight difference in the mics?


When working on them I was holding in my hands both together at the same time. I could not find any differences. No idea how the Schoeps circuit in the same body from the same factory on the same PCB with the same capsule could give different measurements :shock: .
Maybe they were measured on a different day...  :wink:

As I stated earlier, I traced the MXL990 schematics and it is MXL603 on a different PCB.


Marik,
That is good to know as one can get a MXL 900 pack(a 990 + 991) at banjo center for the price of a 603. But makes me go Human error on the testing or they fudging their numbers to make it seem like two differnt mics? As per the mic data sheets there are differences ... I dunno I am so confused now :wink:


My speculation is that because of price match issues, nice folks from GC could not sell 603 cheap enough, so the MXL made the 991 and slightly "changed" curves, to avoid suspicions.


Are you sure this isn't an electret? That might explain both the price and response changes.


It's all about the "He said... She said b...s...!  :grin:
If I can't fix it, I can fix it so nobody else can!
Frank's- www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar- http://tdsl.duncanamps.com/schematics.php

Gus

MXL 991 mod
« Reply #17 on: March 16, 2006, 06:15:10 PM »
if it has the DC to DC converter section I would think it is a external charge type.

Marik

MXL 991 mod
« Reply #18 on: March 16, 2006, 06:18:13 PM »
Yes it has. I also took both capsules apart.
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones

pucho812

MXL 991 mod
« Reply #19 on: March 17, 2006, 10:32:51 AM »
Just opened a 990 yesterday. It's a semi upgraded 603. This one had 1Gohm resisters comming off the capsule @ r1 and r2. No longer had a trim pot like the 603 but otherwise identidcal. PLus at the moment GC is selling that along side a 991 for 99.00 without negotiations.  NOt too bad for 2 mics that can be modded. MY buddy got 2 sets 4 mics total for 216.00. Going to mod them out. Hell maybe even scrap the 991 capsule. Will post pics as events warrent.
Every mic has a purpose it might be a door stop or a hammer, but every mic has a purpose.