AKG C480B to Neumann KM84 - Done!

Hi Everyone,

I had a pair of C480B mics that were defective and refused to pay the minimum $250 fee that AKG quoted me to repair them.  So, I contacted Russell Technologies and asked if I could get a KM84 circuit designed onto an AKG board layout.  I created the pcb outer contour in AutoCAD with all hole sizes and positions, and I found exact replacement switches on the Mouser website.  To start, the mics looked very much like the ones in this photo:

http://cdn.recordinghacks.com/images//mic_extras/akg/C480B-cutaway.jpg

I removed the plastic capsule connector and the XLR connector from the original pcb and reused them on the new board.  This is my first total mic rebuild and I'm so happy with it that I thought I'd post a pic here.

However, after trying several times, I could not upload a jpeg to my message; I kept getting errors.  If anyone can tell me how to get my picture up, I'll do so.

Cheers!
Gord

Try to rename images

Are they jpg?
Best,
Bruno2000

Finally, the pic is attached and it works.  Let me know what you think!

Are the capsules good?  You should see around 40 pf and no resistance across each capsule using a low voltage capacitor checker.  Look up the capsule capacitance in the manual to be sure of the correct value.

I don't think that AKG publishes the capacitance.  I looked up the owner's manual and the service manual and it was in neither.  I imagine that my capsules are all in good shape; Richard Land of Land Audio serviced them about two years ago and they all came back to me as good as new.

that's pretty cool.. I'm impressed.  How does it affect the general sound signature ?

It sounds nothing like the original mic.  The C480B was open and clear sounding, while this new one has a character to it that's hard to describe.  I actually think it has a vintagey vibe to it.

I can try to make a recording with it, as well as with one of my transformerless-modded C460B mics and post here for comparison.

Very nice! I´m wondering how it sounds as well. The comparison you mentioned would be very much appreciated.

Have you thought about offering this as a DIY kit?

Here's the link to the comparison files:
https://soundcloud.com/user-804555278/sets/akg-mic-comparison

C480B modded to KM84 versus C460B with Jim Williams mods.  Go ahead and make fun of my guitar playing, I deserve it!  I swear I used to be a lot better! 

Robert from Russell Technologies designed the board and I can post my bill of materials here.  Other than the jfet from Linear Systems and the transformer from AMI, everything was ordered from Mouser.

Let me know what you think!  How do you think they compare?  I hear a hair more lower-midrange from the 84 and a touch more air from the JW.  Both excellent and kudos to Robert for designing the board.

Thanks for uploading!

I listened to it on my consumer stereo system so far.
I think both have their qualities. I do like the charakter and midrange clarity of the 84ish circuit.
What was the overall cost of the modification?

How does the modded C460 compare to a stock C460? I have a couple of those but never felt that there´s anything wrong with them. Nice clean amp with little coloration and good linearity. For more character and softness there´s the C451.

With capsule was used?

That was the CK61 cardioid capsule on both.
Once I have a pair, I'll post a proper recording in a good ambient space.

When I have some time, I'll tally up the cost of this project ... it might take a few days but I'll do it.