MXL 603 -> KM84 Replacement PCB

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GraemeWoller

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Just putting a feeler out for a drop-in replacement for the stock MXL 603 series PCB.

The MXL 603 is boring. It sounds boring and it is boring. It's a overly boring bright/brittle version of boring. It’s cheap for a reason.
The Neumann KM84 is not boring. It's awesome. It's got thickness. It's got iron. It's got thick iron. It's basically the opposite of the MXL, which doesn't have iron. It doesn't even have lead in it's pencil.
The MXL 603 KM84 replacement board takes the circuit from the KM84 and uses your old MXL as a donor body, capsule and XLR connector.

You're building a MXL 603 with mojo.

What I'm thinking is: I'll provide the PCB, the schematic, BOM, and a build guide, inc. postage to wherever you are for US$30 each. You get the parts and put it together, and BLAM! you've got a better sounding mic than you started with.
It's an easy DIY, and if you have the mics around you might as well make them better.

nb. This ain't going to work if you want to chuck it in a Banzai style body. The PCB is a different length, and the mounting is different at the XLR end. It's for MXL mojo, not other mic mojo.

Let me know if you’re interested, we'll need a few to make it worthwhile. :)

Graeme
 

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Khron

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Attachment doesn't work(?).

And just how much will the new electronics alter the sound of the capsule, actually?
 

GraemeWoller

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Yeah, you're quite right about the attachment, I'm having no luck with that.

re: the electronics altering the capsule, it doesn't. The signal path sounds nicer though. I certainly didn't mean to insinuate that it would change the capsule.
 

Khron

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"BLAM! you've got a much better sounding mic than you started with."

Eeeeehrm...? :D
Khron said:
And just how much will the new electronics alter the sound of the capsule, actually?
 

Khron

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I didn't mean to say it was worthless - it's always nice to have options :)

It's just that the claims didn't exactly "compute" :D But then again, i'm possibly a bit more pragmatic / cynical / [something else] than many / most other people involved in this sort of area :p

For what it's worth, a while ago i also drew up a KM84-ish circuit and board (with the Neutrik NTE10/3) for my t.Bone SC140's (which are, i think, Rode NT55 knock-offs), just for kicks. Still haven't gotten around to making any physical prototypes though ;D
I did physically make a pair of Oktava circuits for the same mics years ago, just to avoid all the MLCC's in the stock signal path (a bit of a pet peeve of mine), but reusing the DC/DC converter. One did get installed into a mic, but the sensitivity was somewhat lower than stock. Haven't bothered inspecting it any further yet, though :p
 

GraemeWoller

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Yeah, I thought if nothing else it's a fun thing for folks to build, it's not exactly for high-end DIY gurus. ;)

From my listening tests changing out the board, using the different circuit with better components, seems to reign a bunch of the top end nastiness in the stock capsule. It's not pretending to be a Slate Digital emulating mic of course. ;) No harm in being pragmatic though.

I'd love to hear what that circuit would sound like in your t.bone. I've never had one up on a source, so I have no idea what they sound like stock. I've found the NT55s a little bright, but generally not too bad though.

There's no doubt about it, the biggest change is going to come from the quality of the capsule, but I do boards not capsules so this is my part of the chain. :)
 

Khron

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I think / hope i'll get around this summer to running some measurements on my SC140's. I "Joly-modded" three of the four capsules (ie. cut out the "bar" in the middle of the vents, thereby widening them, which should tone down the mid-highs by a couple dB, and bring up the high-highs).

But i plan to run sweeps of all four combinations (100% stock, stock capsule w/ Oktava circuit, modded capsule w/ stock electronics, and modded capsule w/ Oktava circuit). Only bad thing is i don't have a Rode NT55 to compare :D

GraemeWoller said:
I'd love to hear what that circuit would sound like in your t.bone. I've never had one up on a source, so I have no idea what they sound like stock. I've found the NT55s a little bright, but generally not too bad though.
 

rockinrob86

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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.
 

Icantthinkofaname

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Would high frequency attenuation help the capsule? I know Mic-Parts sells a replacement circuit that includes it and claims it'll make the mic sound a lot better. I just don't know if Neumann's SDC capsules were intended to have the high frequencies rolled off.
 

rodaffleck

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I'd be interested, especially if someone with better logistics skills than myself were to organise a capsule and transformer group buy from 3U or some other equally affordable company.
 

rockinrob86

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You guys are going to make me end up with 8 of these things!  I'm going to be drowning in KM84's!

I posted these in other threads, but since we're here...

This one has a bunch of SDCs on an acoustic guitar for a song.  Same verse looped, one of the mics is the 3/u capsule and graeme's km84 guts with a cinemag.
https://www.youtube.com/watch?v=vJ9Rz-SbjLs

This one is a real KM84 vs the "clone" on a different acoustic guitar/vocal thing and then a drumset as a mono OH.

https://www.youtube.com/watch?v=nVJxx7YM-6I


the drums are really the only place I hear a difference.  Real KM84 is a little softer on the highs/transients.  But the point is, the "clone" sounds great and is usable and awesome for the price.  I've been using these on toms and think they are awesome in that role, and I don't have to worry that much about them like you would with the real deal

 

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