Anyone mod a MXL with the KM84 output?

I busted open my new MXL 990, and was thinking of replacing some of the caps, however I came across the schematic for the KM84 (very simple layout)
http://www.gyraf.dk/schematics/Neumann_KM83-84-85.GIF
And was gonna grab a 15K : 200 CT (8.7 : 1) transformer from cinemag.
And try to cram this all in the case...
The 2N3819 is available through mouser actually all parts are rediliy available...

Anyone done this before?
Any pitfalls?

Thanks!
~Andrew

Did you search?

yes, I have searched, I know people mod the 990's all the time, I was wondering if anyone has Spesifically replaced it with the KM84 guts, and putt a transformer on it?

From the meta meta

I have and a few others have

http://www.groupdiy.com/index.php?topic=234

has one

search for KM84

Also go to neumanns site and look for the PDF "microphones"

I walked past an MXL at GC yesrterday for 129 out the door.
Worth the price just for the body and screen me thinks.
We were ready to close the deal when I asked for the extended warranty-on the house. I figure after I barf it all up trying to DIY a decent mic, and it ends up ready for the dumpster, that I can trundle on back and demand a full refund and start over, right?
I mean, this is the American Dream in action. Put it all on the card.
Thats when things started to get ugly. First off, here comes some punk-azz manager, wanting to know what all the fuss is about.
So I tell him that his crony here, the geek with the flat top haircut and the clip-on tie, that I'm comin back with my strap, and my crew, to clean the place out.
So him and his friend start pullin the tag team on me, tellin me to take it down the street, otherwise it's gonna be the cops.

So I start talkin bout how I have their address, but they don't have mine, making it very easy for me to burn down the whole store, which puts them out on the street, ready to wander off and die behind some pruno drippin dumpster in a dimly lit alley somewhere, seven blocks south of Market, in their sneakers and bathrobe, with an empty bottle of ripple.
So they start talkin bout how They make the rules, and how White Boy #1 is about to bounce.
Even with my deaf ears, I could hear the sirens, so I had to bail.
Musician's Friend, I guess.
:twisted:

hmm, interesting story CJ, not very helpfull, but funny nonetheless..

Gus, I saw those links, and those are the larger diaphram MXL's and they are TUBE designs, I'm wondering if anyone has re-created the KM84 circut on a less than 1" diaphram mic... I searched KM84, lots of talk, but cant find a link where somone has actually done it... so I guess I"ll boldly go!

Maybe we could talk Dale into doing a small run of small diaphragm capsules for us.. I'd be in for sure

A real km84 is built in a 3D way inside the body.

I agree finding a transformer that would fit is a issue.

I put a KM84 type circuit in a v67 and a piece of fence post

[quote author="CJ"]with an empty bottle of ripple.
So they start talkin bout how They make the rules, and how White Boy #1 is about to bounce.
:twisted:[/quote]

Good stuff man. you got me laughing pretty good. anyone else think this story sounds like it could be a K-fedderline rap song?

I've got a KM-84 here (I keep one on my bench to test new mic preamp designs)., I could be convinced to pop it open and take a picture if one isn't already available on the web somewhere. it is indeed a 3-D construction, and is a little bit hard to describe with words.

mike

I ripped that from 40 yr Old Virgin.

anyway, Stephen Paul, wasnt he the man on those 84's?
I remember a lot of people saying he made thos things sound like God, matched stero poairsa for overheads, etc.

Hmm. looking at that km84 circuit got me thinking. I bet this DI circuit I designed, with a little optimization, would make an ok mic head amp.

No commercial use without permission!!

I didnt try to simulate, this is an as-built drawing. I found that by trimming the gain of the first FET (R6), you can cancel out some of the distortion products. it also changes the balance between odd and even harmonics, so you could also try to tweak it by ear. it sounded good as a DI, clean and pure at low levels, a little bright and foreward when pushed, but in a good way. I don't mess with mics much, but maybe someone else will want to try this?

mike p

That's clever Mike. I've never seen anyone differentially drive a transformer with an all FET circuit. So you've got a common source amp feeding the top of the transformer primary. A source follower with constant current source into a common gate feeding the bottom of the primary. Cool.

EDIT: I'm an idiot, no inversion through source follower and common gate.

[quote author="Gus"]
I agree finding a transformer that would fit is a issue.[/quote]

Maybe try the Beyer models - that's what's used in my Beyer 720 SDCs and I really like them. I could check which model they used in case it is not a mic-input model.

I put a KM84 type circuit in a v67 and a piece of fence post

Click to expand...

How did that sound? I'm not familiar with how circuits are optimised for SDC or LDC capsules and whether this would make much difference....


CJ - that story was hilarious.

I did make up one SDC capsule. It was a lot harder than LDC's. After I recover my sanity from the last M7 run, I might do some side-address smaller capsules - kinda like the ATM450 or a single-sided version of the CM7156. I don't like doing double-sided capsules that much any more.

I've made the KM84 circuit and used it on an AKG CK61-ULS capsule. Sounds nice. I used a Beyer transformer. Those capsules are reasonably priced (around $300) considering how good they sound. On my recommended capsule list. Gus, have you tried them?

-Dale

Mike, why do you need that diffamp and harmonic balance change at all?

[quote author="Wavebourn"]Mike, why do you need that diffamp and harmonic balance change at all?[/quote]

I wanted to try parallel FETs for lower noise. and to try something different, take the outputs different places. it is push-pull but is asymetrical, with the intent of keeping some even products in the residual. in practice you can trim it like I noted. so why not? it sounds different, try it.

mike

[quote author="mikep"] it sounds different, try it.
[/quote]

Sure it is.
Couple of paralleled diodes in series with output may give you more difference.

[quote author="Wavebourn"]
Couple of paralleled diodes in series with output may give you more difference. [/quote]

you must LOVE the sound of diode clipping, you mention it in almost every thread.