Well here's my review of a C12type microphone I built. First time I have tried to build a mic and it wasn't without some growing pains. The first one took me about 2 weeks of basically staring at a schematic wondering where I went wrong and why the bottom end was weak and no reach on the mic. Basically 4 hours of building and a hundred hours of staring. It turns out I had a faulty xformer and I had built the mic correctly from the get go!
Capsule: CT12 by Tim Cambell
Valve: GE 6072 5 star
Xformer: Tab Funkenwerk Hiller Type 14:1
PSU: Tab Funkenwerk
Cable: Gotham Audio GAC 7
Resistors: NOS as per original, except for the shunts which were ohmite's
Capacitors: NOS polystyrene as per original. Coupling cap: V-Cap - (Oil Impregnated Metalized Polypropylene) 1.0uf as opposed to .5uf as called for in schematic.
Note on coupling cap. Originally I went with a Solen SM series .5uf cap because I couldn't find a suitable PIO cap (I still wouldn't mind trying) but when I was having the bottom end troubles I spent too much money on a V-CAP with a 1.0uf value in hopes of squeezing some more low end. At that time I didn't know the issue was with the xformer. I should mention that TAB replaced the xformer no questions asked, nor requesting the old one back or charging for shipping, and in a timely manner.
And speaking of vendors, Tim Cambpell had phoned me months after I bought the capsules from him wondering how I liked them and offered tuning changes if I had any different preferences. He also mentioned that he tunes them on the side of bright as opposed to dark as that is his preference, and as it turns out it was my preference as well. According to Tim, his capsule uses the original NOS gold sputterrd membrane that AKG used to skin his CT12's that he had acquired. My only complaint would be that the tab on the side of the capsule protrudes a little too much to fit in the headbasket comfortably. I mentioned it to him and he offered to rectify it, but I was able to do that myself without much trouble. But in fairness for an honest review, it should be mentioned.
The mechanical kit from flea is nice piece of work. I'm not sure about the headbasket. It seems a little too square at the top corners, more like an Ela m 251 and a little higher. In my research in how to build this mic, it seemed to me in pictures that the head basket was slightly rounded on the corners and not as tall. Perhaps someone could share some light on the subject for me?
One thing about the kit. It was designed to use a Haufe T14 xformer. Because I chose the Hiller, the screws to hold the xformer in place were not long enough and you would have to buy longer screws.
The PSU seems to be very well built, fat traces, historical look, and built to historical specifications so that I could bias the mic using the original methods.
So far I have used the mics on about 2 dozen session, from acoustic guitars, drum overheads, male and female voice, piano rooms, drum rooms, and back ground vocals. It has always worked well, and has always returned very good results. I should mention that the two mics are close in sound, very consistent with eachother although if you critically listen, one has slightly more in the high frequencies. So not perfect.
I've included 3 wav files. Keri Latimer ("Nathan") was kind enough to give me permission to post these here. 2 of these files are from a mic shootout with absolutely no processing. The chain was mic->Helios type 69->UA2192->PT 44.1/24. Unfortunately there was noise in the stuido when we did the shootout and the gain was low on the preamplifier. I have included the final track used on the record to get a better quality recording here, but the caveat is that it was going through an LA3A compressor hitting at the most 2-3dB GR at peaks - but still premix no eq or effects. IIRC, the demo's might have been sung 18" - 20" inches from the mic where I believe I had Keri move up a bit to 12" - 18" from the mic. All patterns were cardioid.
I've included the mic we shot my C12 against for interest sake. It was a Telefunken U47AE made in USA using the identical chain.
Okay the wavs:
C12 Demo: http://empirerecording.ca/review/c12
U47 Demo: http://empirerecording.ca/review/u47.wav
C12 Final: http://empirerecording.ca/review/c12