DIY / "fake" C414 or CM414

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Khron

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A while ago, i was fortunate enough to discover that Advanced Audio Microphones actually had offices within Europe, and a whole dedicated website.

I was considering seriously getting into mic modding and capsule replacements, but with all the other "3rd party" capsule manufacturers being US-based, the whole idea of having to pay customs and/or VAT on top of 100-200$ capsules was a real downer.

And here's where AAM came into play - quality-looking capsules, for pretty reasonable prices (~100eu), without the worry of customs. As an extra bonus, i could even buy products from them ex.VAT  ;D So i went for a pair of their AK12 capsules, which ran me up a total of 177.60eu - NOT BAD  8)

Then came the stage of looking for as-cheap-as-possible donor mics. I wanted multipattern ones, and the most affordable ones i managed to find were a pair of Devine BM600's from Bax-Shop. My hunch is they're some re-branded iSK BM600's, perhaps? Either way, for about 75e per piece (ex.VAT, 89e incl.VAT), it was all i could've asked for. Hey, they even come with a shockmount, windguard and suitcase!  ;) Unlike Chunger though, i was fortunate enough to have caught two properly-assembled saddle mounts, so no worries there  :)

You can find some lovely-looking internal photos of the stock mic (better than i can ever hope of pulling off) over here: http://groupdiy.com/index.php?topic=49389.0 - just scroll past the U87's.

To be honest, i was almost shocked to see so many film caps(!) in what would otherwise be a bit of a "bottom of the barrel" mic  :) The circuitry seems to be identical to the one in the AKG Perception 200 / 220 - you can find a (partial) lifted schematic over here: http://www.audioimprov.com/AudioImprov/Mics/Entries/2013/2/26_AKG_Perception_220.html

Full U87-type EQ circuitry, 2SK30A-Y JFET, and a 2SA1015 PNP driving the actual transformer. Not bad, all in all, if i may say so myself.

Now on to the mods - ripped out nearly ALL the components from the input board and the output board. The only stock components left were (or are) the transformer, and the inductors & ceramic caps right at the output pins.

I wanted to go all out, and match all the replacement components between the two mics, as close as i possibly could, in the attempt of being left with something i could call a "stereo pair". You can see the stock schematic in the first attached photo, while the final schematic (including new component values, in some cases) is in the 2nd one.

I had a few headaches with the DC-DC converter, though (see the U87A schematic). Out of the factory, the voltages it put out were in the region of +/-45v or 50v, can't recall exactly right now. Several LTspice simulations later, i stuck a pair of 5.6V Zener diodes in anti-series with the 1N4148 (which was in the D7 position seen here: http://recordinghacks.com/images/mic_extras/neumann/u87ai-schematic.gif ), and dropped the values of the two input resistors, while increasing the values of the filter caps. Stock, the circuit had 7.5k - 330n - 5.1k - 10u. Post-mods, that turned into 2.2k - 330n+470n - 1.1k - 47u. This resulted in output voltages in the 68-70v range - muuuuuch better  ;D
 

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Khron

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Modded / final schematic (signal-path only, no DC-DC)
 

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Khron

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Modded input board (200pF styroflex cap for the pad, J305 JFET)
 

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Khron

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Modded output board (2SA970 output transistor)
 

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ln76d

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You posted K67-copy pictures, and the schematic is not readable for me.
Did you used quasi u87 perception/mxl/many chinese mics topology with emitter follower and 2:1 transformer?
Is there deemphasis feedback path?
BTW. chinese "CK12" have much more common with k67 than with real CK12 - you can look on it like the edge terminated k67 copy.
 

Khron

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If you'll read the description more carefully, that K67-copy picture is of the stock mic. And what exactly isn't readable, in the schematics? :)

No, i removed the U87-like de-emphasis circuit (the missing components from the post-mod output board), which DID exist in the stock circuit (see post #1).

The capsules i used were these: http://advancedaudio-europe.com/Mics-Parts-DIY/AK12-Capsule
 

ln76d

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Khron said:
If you'll read the description more carefully, that K67-copy picture is of the stock mic. And what exactly isn't readable, in the schematics? :)

Sorry, i didn't read carefully  :)

The shematic ;D

Khron said:
No, i removed the U87-like de-emphasis circuit (the missing components from the post-mod output board), which DID exist in the stock circuit (see post #1).

The capsules i used were these: http://advancedaudio-europe.com/Mics-Parts-DIY/AK12-Capsule

Isn't microphone too bright for you?
I even tested this type capsule (same factory) in C414 circuit and it was too bright for me.
Not big difference when testing in the same circuit in comparision with k67 copy.
In my opinion, for this capsules,  deemphasis path makes great job and there is also possibility to tweak low fequencies response.
 

Khron

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"Unreadable" = you can't see the screenshot, or you don't understand what's in the schematic? :)

I've yet to actually use them in a recording scenario, but my band and i ARE preparing to record our new album in the near future, and i'll very likely be using these as overheads, so... I guess time will tell :D

But before that, a live-sound-guy friend of mine said he'd like to take them out to a gig, to compare them at least to his pair of C214's (yes, i know, they're different-sounding AND they're electrets ;) ).
 

ln76d

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I see the screenshot, but it's like gymnastic to my eyes  ;D

It's good to compare with C214, becuase it also has HF bump, try to record them on live gig or just take crash cymbal and record it.
AK12 should be brighter than C214.

Here's frequency response for cordioid of Dave CM12 (there's no chart for CM414)
http://advancedaudio-europe.com/image/cache/data/mics/CM12_SE_Cardiod_large-800x800.jpg

I don't know what sits inside CM12, is there any hf filtering?!? I assume that there's no filter, so HF response is not so bad, but still boosted.

Response of C412/C414 (brass CK12) cardioid attached.
You could get much closer response with AK12 using deemphasis filter :)
Did you biased FET?
 

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Khron

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I'm starting to wonder in what way would the various headbasket shapes affect the sound...

Frequency plots of C12 and ELA-M251 (both using the "vintage" CK12) seem to have quite a bump in the 10kHz area, BUT also both of them have cylindrical headbaskets. The C414's have that well-known flat-faced headbasket, and for example the C414EB seems to have a pretty flat response.
 

ln76d

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It always affect somehow - shape, the number of mesh layer,  mesh density etc.
Bigger symetrical headbasket should be much more transparent.
Don't forget that many circuits aren't flat ;)
C12 had circa 3dB hf bump and fall after 15kHz. Still less.
Every chart for C414EB which i have found is for "teflon" capsule (which i really like), and it had different response than "brass"CK12.
That's why i attached C412/C414 response - it's for sure "brass" CK12.
 

ln76d

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Shame that they didn't wrote which C414 it is...
I like comparision samples  where is only one source to compare.
I hear the (little bit nasal) high-mid and high frequency boosted.
It sounds more edgy, somewhat you can find in many chinese microphones,  but probably it's better than many chinese microphones :D 
I believe that Dave knows what he's doing.

If I had to compare to other microphones, it sounds much more like quasi u87 copy than C414 (maybe a little bit like later version of c414 with boosted highs).
I would need to compare it on my recordings to have an true opinion.
Unfortunatelyy samples don't show even 50% of microphone possibility.
Important is to match microphone to the source!

Before you will try to record with your band, try it first on some cymbals and you will see what is really worth :)
The most important thing is that you should like how it sounds ;)

You know why many samples of manufacturers (especially chinese) are made mostly with vocals and acoustic guitars?
Because many of shitty microphones will work with acoustic guitar in pleasant way, but put same microphone on drums (OH for examples) or sax, violins and they sounds crappy.
This was not about the AA microphones or stillwaterstudios  sample of course ;)
Only a clue!
 

Khron

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I guess you make some fair points (about sound examples etc), but there's something to be said about the fine details in vocals + acoustic guitar as well - if all you needed was SPL tolerance, you'd go with dynamics :D But indeed, the right mic for the right sources is the only ("right") starting point :)

About recording - ironically enough, drums is what we'll start with anyway, and it's gonna be real interesting to both engineer AND track / play the drums as well ;D But fortunately, after i get everything miked up and set up, i'll have the guitarist as an assistant :) (at least for "pushing the buttons") And i've got some reasonably nice cymbals too, so... hoping for the best, really.

It DEFINITELY can't sound worse than the first album the band recorded themselves, not long before we got in touch and i joined them, in march of last year :D And for what it's worth, i managed to successfully pull of my first engineering gig this summer, tracking drums for my guitarist's other band, and they were real happy with the resuly, so... I guess i can't be TOO horrible at it :)
 

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