MXL 603 -> KM84 Replacement PCB

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GraemeWoller

Well-known member
Joined
Mar 5, 2017
Messages
124
Location
New Plymouth, New Zealand
Good morning everyone.

I'm sorry about the long quiet stretch, there's been a bit going on, but I'm above water now and I have new stock of the MXL KM84 PCBs ready to go. It's a wonderfully simple circuit to DIY, and a great way to add a little extra spunk to any 603s you have around. (Plus it's fun).

Those who have already PM'd me have received messages directly letting you know what's going on.

Hit me up if you're keen on getting a board or two.

Rock On!

G
 

GraemeWoller

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Joined
Mar 5, 2017
Messages
124
Location
New Plymouth, New Zealand
Hey everyone,

I hope you're all keeping safe and healthy where ever you are in the world. This thing's having such a huge impact all over, and I hope you're all ok.

I just wanted to say a big thanks to everyone who's been interested in the PCBs so far, I really appreciate it and it's been a wonderful vote of confidence in my little project. Thanks!!  :D

Stay safe everyone!!

xx

G
 

GraemeWoller

Well-known member
Joined
Mar 5, 2017
Messages
124
Location
New Plymouth, New Zealand
Gidday folks,

Life is returning back to normal here in New Zealand, (our people have done a really great job of keeping us safe over the last month and a bit), and the post office has opened up for service again. If anyone is interested in getting one of these KM84 MXL 603 replacement boards I can finally start getting them out to people.

I hope everyone is in the safest of situations, I know there's so much weight on everyone's lives right now, but stay safe in whatever space you're in. Keep well!

xx

G
 

GraemeWoller

Well-known member
Joined
Mar 5, 2017
Messages
124
Location
New Plymouth, New Zealand
"Graeme, any reason why you changed C4 from 1uf to 4.7uf?"
Hi Jerry, yeah the reason I originally changed C4 is because I had a bunch of 4.7s and no 1uf on hand when I was testing this circuit out. I poked the 4.7uf in there as a stop gap in the early days and found no audible difference so it's stayed that way.

"These were draw mistakes, C4 and R4 drain resistor, hopefully corrected to original schematics."
Nope, C4 wasn't a mistake, it was a choice for the reason above. BUT, I'd encourage anyone who wants to change it out with the original value to give it a go. It's no extra effort, or confusion, and I'm always super-happy to hear about what other people have noticed and heard. Please post up your observations if you have any.

I'm not sure what you mean about R4 though. That hasn't changed from the Neumann schematic. Could you flesh out your thoughts on R4 for me, please?
 

Leslie 123

Member
Joined
Jan 21, 2019
Messages
21
Yes, not so mistake,  C4 must be large enough to hold the voltage across itself constant at audio frequencies so the signal passes on to the transformer primary.
 

JerryPbury

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Joined
Jun 6, 2004
Messages
73
Location
Charlotte, NC
rockinrob86 said:
I got a couple of these from Graeme and they have become foundational mics for my studio.

In the us, you can buy mxl 603/991 for $30 really easily.  I ended up with 6 or 7 of them and did the “gus” mods that were popular years ago.  All of the capsules are different, and some of them are much better than others.

The gus mod sounds pretty good.  The km84 pcb with a cinemag sounds noticeably better. 

I ordered 4 capsules from 3u audio, and those sound way better!  In fact, a head to head comparison with my real km84 revealed that on some sources they were indistinguishable, and on others they had a different flavor, but were still really good sounding.

I’ve been using the 603 with graeme’s boards, cinemag transformer and 3 u capsule on toms and acoustic guitars, and they are really awesome on both.  On toms I love how the leakage is natural and not that crappy dynamic kind of annoying leakage you have to worry about.

What did you have to do to the 603 to get the 3U capsules to work?
 

kato

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Joined
Aug 16, 2004
Messages
1,575
Location
Indianapolis, USA
What did you have to do to the 603 to get the 3U capsules to work?
I think they're a match, no modification needed. (Not entirely sure, but one of Banzai's posts in the Lulu thread seems to indicate that the threads are a Chinese standard shared between MXL, 3U, Lulu, and several other brand rebadges.)
 

kato

Well-known member
Joined
Aug 16, 2004
Messages
1,575
Location
Indianapolis, USA
Do you guys mind sharing what FET you're using in place of the 2N3819?

I'm feeling adventurous. And the original Neumann schematic looks "simple" (relatively speaking) enough to breadboard. And I'm afraid the 2N3819's for sale out there are probably fake. Thanks for any FET advice you might have.

Erp. Nevermind. Mouser sells 'em for a buck. I mistakenly thought they'd been deleted.
 
Last edited:

Migs 31

Well-known member
Joined
Mar 29, 2010
Messages
63
Thank you, thank you, thank you!!! A thousand times.

To Graeme for this project.
I got two of his PCB's and built them during the second lock down in Europe.
I could not source all the parts I wanted, so I had to improvise with parts I could find. But the two mics sounded very very good to me. I used two APEX 180 as donors, slightly different insides to the MXL 603, but with a file and a bit of patience Graeme's PCB's fitted just fine.

The result was day and night compared to the originals.

I have been recording a Kiwi (New-Zelander) artist, John McClean in London over the past month & the MXL 603-KM-84's have been used over Guitars, Percs, Drums O.H. and even SNARE!!! (more on that a bit later).

And yes I had to compare with a pair of Neumann's and other SDC's we had in studio.
Result, Graeme's versions of the MXL603 KM-84 won (to my ears) most of the time.

I'm a very satisfied sound engineer/musician with these.
:0)
M
 

Attachments

  • MXL KM-84 PCB-1.jpeg
    MXL KM-84 PCB-1.jpeg
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  • MXL KM-84 PCB-4.png
    MXL KM-84 PCB-4.png
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  • MXL KM-84 DOBRO GT.jpeg
    MXL KM-84 DOBRO GT.jpeg
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  • MXL KM-84 SNARE.jpeg
    MXL KM-84 SNARE.jpeg
    81.3 KB · Views: 34
  • MXL KM-84 CONGAS.jpeg
    MXL KM-84 CONGAS.jpeg
    107.7 KB · Views: 32

GraemeWoller

Well-known member
Joined
Mar 5, 2017
Messages
124
Location
New Plymouth, New Zealand
That's awesome to hear, Migs! And doubly-awesome to hear you were using it on a Kiwi artist. It's amazing how versatile these wee mics are after the mod. (well done on the file and patience, btw! 😁)

When the project is finished I'd love to hear the results!!

xx

G

Thank you, thank you, thank you!!! A thousand times.

To Graeme for this project.
I got two of his PCB's and built them during the second lock down in Europe.
I could not source all the parts I wanted, so I had to improvise with parts I could find. But the two mics sounded very very good to me. I used two APEX 180 as donors, slightly different insides to the MXL 603, but with a file and a bit of patience Graeme's PCB's fitted just fine.

The result was day and night compared to the originals.

I have been recording a Kiwi (New-Zelander) artist, John McClean in London over the past month & the MXL 603-KM-84's have been used over Guitars, Percs, Drums O.H. and even SNARE!!! (more on that a bit later).

And yes I had to compare with a pair of Neumann's and other SDC's we had in studio.
Result, Graeme's versions of the MXL603 KM-84 won (to my ears) most of the time.

I'm a very satisfied sound engineer/musician with these.
:0)
M
 
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