Transformer Build with The Twelve Twist

I recently bought yet another cheap MXL 910 on ebay. As I was considering what flavor to make it, I noticed a box of long-forgotten CK12 style capsules on the parts shelf. Earlier on, I was working on a CK12-ish flavor of my transformerless mics. I quickly ran into quality issues with these capsules. They sounded great – when they worked. But at one point, I had only two out of a batch of five that were useable. They are made at the same factory which makes my extremely high quality k47 style capsules, so it was a disappointment. Anyway, I sort of abandoned the “12 flavor” – maybe until now.

MXL 910 mic mod with c12 capsule
The Finished mic (with fancy sharpie c-12 label)

The key thing that sets the CK12 apart from the k47 is that it is edge terminated. As you can see below, there is no wire coming off the center of the diaphragm. Instead the white diaphragm wire is attached to the edge of the capsule. The classic AKG-ish sound of these capsules is an extended smooth and silky top-end.

c12 style capsule
Edge Terminated C12-style Capsule

CK12 style capsules do not always fit that well in some BM800 style headbaskets because of the height of the stand-offs for the backplate wires. The MXL910, however, has a nice big headbasket which easily accommodates a CK12.

Transformer or Non?

But, should it be a transformerless mic? Or should I go transformer-coupled? While pondering that decision, I thought about the results I’ve had with the Tab-Funkenwerk transformer I’ve been using. They have a very fat low and low-midrange and can tend to sound a little “dark” overall. But a CK12 is a brighter capsule! So maybe a CK12-style capsule in a transformer coupled mic with the Tab-funk tranny could be pretty cool!

building a ck12 mic into a mxl910 body
The Creation on the Bench

What we have here is a mic with a CK12-style capsule, a KM84 style circuit and a T12-style transformer. Will it be an abomination of nature or maybe something special?

These Go to Eleven

As soon as I plugged this in to my test mixer at my workbench, I knew I was onto something. The fatness and fullness in the lows and low mids of the Tab-Funkenwerk tranny combined with silky bright top end of the C-12 is pretty amazing. After one quick test on acoustic guitar in the studio, I’m pretty excited. It has lots of everything. Full lows without being boomy. Silky highs without being harsh. And a nice bit of transformer crunch/compression that I expect from the AMI transformer. The mic output is hot! I might experiment with a fixed 3 or 6db Pad. On the other hand, that strong signal is probably contributing to the extra crunchy saturation of the transformer so maybe I’d opt to pad these at the preamp on loud sources. As always with my test recordings, this is straight into a CAPI vp312 preamp with no EQ or other processing at all. The Guitar is mic’d from about 20 inches away with the CAPI preamp gain on the 2nd from lowest setting.

A Worthy Addition

This is not the most versatile mic I make. I’d say my good ol’ transformerless mics with the k47 style capsules take that prize – they work great on anything. But this mic would be beautiful on vocals, acoustic guitar (and other stringed instruments) and percussion. I would probably not reach for it to use on a guitar or bass amp or kick drum. For sure, it’s another fantastic flavor and this particular one will find a home in my personal collection.

Not sure yet if I will add any CK12 flavor mics to my list of standard offerings in the store. Although this particular capsule is working fine, I’ve had a bad experience with them in the past. Maybe I had a bad run of them. Maybe not. I want to see how this one works over the long term for a while and maybe try another build or two before I start offering them to non beta-testing customers.

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