Searching for "generic" microphone electronics, how to switch patterns etc.

[KarenColumbo]

I guess this is a bit OT, because it does not touch the "Stompbox" area completely (except in moments of complete frustration).

I recently got hold of an original (new) AKG C414 XLS capsule and a few panasonic WM-61s.

The 61s are pretty straightforward, I'll try and make omnidirectional "lipsticks".

An entirely different beast is the double membrane CK12 capsule. Rather than "clone" the classic C414 (which I think is bound to fail, I'd never be able to get near the original quality) I would like to build a "learning mike" where I can learn all there is to learn about polar pattern switching, hi and lo cut and dampening etc. 

Now some googling brought up the oringal AKG service manuals with schematics that I'll have to redraw to make them readable to myself. Than there's the seemingly ubiquitous "Schoeps style circuit" which doesn't apply here because it lacks the pattern switcherooity -> omni.

Do some of you gents have one or another schematic in your archives of electronic wonderland that would work with said large diaphragm capsule?

Is there a book or several that specializes in microphone internal electronics?

[Rob Strand]

few panasonic WM-61s.

Those panasonic elements are great.  Not expensive either.

Is there a book or several that specializes in microphone internal electronics?

IMHO, the electronics largely falls back onto designing preamps.    The next layer would be filter by electronics.   This filtering is no different than what you find in a filter book, other than it is applied to microphones.

The overall behaviour of the microphone is combination of the acoustics and the electronics.      The acoustics is about propagation delay due to different distances of the acoustic paths and damping of certain frequencies.   You also get transmission-line effects up tubes.   Tubes are used as delays and you tune the frequencies that get through with damping.   An acoustic engineer deals with all this stuff using circuits but they aren't circuits of electronic parts they are circuits which have the same behaviour as the acoustics.   So electronics uses voltages and currents and acoustics uses pressures and velocities (or volume velocities).    The parts of the acoustic circuits involve diaphragm areas, masses, springs, damping instead of capacitors inductors and resistors.   The electronics kind of helps the acoustic part along.  Some things are best done acoustically and some are best done in electronics.

I'm not aware of any simplified descriptions other than various magazine articles.   More professional stuff is like general acoustics books, which aren't easy to read at all, and a few specialized books.  Some that come to mind are "Acoustics" by Beranek, and "The Microphone Handbook" by Eargle.    Some microphone manufacturers produced nice handbooks which are fairly easy to read and don't have a lot of maths;  maybe Shure and JBL?

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Here's some info on preamp circuits, (and other music industry related stuff),

http://www.thatcorp.com/datashts/AES129_Designing_Mic_Preamps.pdf

[Nasse]

Elektor magazine had some simplish projects or schematics years ago, like https://www.elektormagazine.com/magazine/elektor-200311/17589/ and others. But basically mostly they were based on sum and difference circuits together how capsules are pointed and situated.

I got few low noise sensitive electret capsules and made diy "SASS" mic from scrap plywood and sponge, and dummy head from old headphones and my head, also prototyped jecklin disc

[amz-fx]

Microphones:  https://groupdiy.com/index.php?board=29.0

regards, Jack

[Ripthorn]

I'm an acoustic physicist and routinely work with equivalent circuits as mentioned earlier. All of your directivity patterns are based on the equation a+b cos(theta), if I recall off the top of my healthy properly. Basically it is a linear combination of two diaphragms with a phase. Figure eight is a=0, b=1. Omni is a=1, b=0. Cardioid is a=0.5, b=0.5.

Best resource is Acoustics by Beranek, but expect plenty of math.

Filtering will be done electronically. AKG C414 is my second favorite mic ever.

[Rob Strand]

Is there a book or several that specializes in microphone internal electronics?

Were you going to use a DC converter like the original to generate the capsule voltage?  I suspect AKG  put some effort into making that thing quiet.

[KarenColumbo]

Is there a book or several that specializes in microphone internal electronics?

Were you going to use a DC converter like the original to generate the capsule voltage?  I suspect AKG  put some effort into making that thing quiet.

Yah, that's one of the many hurdles I'd have to jump if I went that way. Not sure at all what to do at this point. But this'd be something where I'd take away a lot for eventual future amplifyer building knowledge, I'd say. Godd friend of mine inherited a matched pair of 414s from his dad - I guess he'd let me take a peek inside and take pics and measurements. AND I got all the AKG service docs from the guy who sold me the capsule - he's an official service technician for this kind of microphones here in Austria. So at least I'd have the chance to have a real close look at the original to formulate a plan

[KarenColumbo]

Beautiful blog
http://audioimprov.com/AudioImprov/Mics/Archive.html

[Rob Strand]

Beautiful blog

Good find.

Yah, that's one of the many hurdles I'd have to jump if I went that way. Not sure at all what to do at this point. But this'd be something where I'd take away a lot for eventual future amplifyer building knowledge, I'd say. Godd friend of mine inherited a matched pair of 414s from his dad - I guess he'd let me take a peek inside and take pics and measurements. AND I got all the AKG service docs from the guy who sold me the capsule - he's an official service technician for this kind of microphones here in Austria. So at least I'd have the chance to have a real close look at the original to formulate a plan

Page 2 about 1/3rd the way down you can see the transformer used in the DC/DC converter.   This one seems to use litz wire although it could be wires tightly twisted.
https://www.gearslutz.com/board/high-end/30334-akg-c414-eb-vs-c414-xls-xlii-2.html

Here's the modern version.   The pot-core has been replaced with an RM core.   Can't see the circuit but it's quite possible it uses a similar circuit, 
https://www.akg.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dwe954f273/pdfs/C414b_xls_xlII_folder.pdf

Similar DC/DC converter on the Sony,
http://coutant.org/sonyc55p/

The AKG seems to 'weakly' regulate the supply but the Sony does not.

These simple converter circuit are deceptively simple.   The transformers take a bit of tweaking to work exactly right.   It's easy to get some working but you can get quite angry supply noise.   The surrounding caps might help smooth out the waveform.  I don't know exactly how smooth the *AC* waveforms are around the DC/DC transformer on the AKG.   You could prod around on an original but man you would want to be careful!


FYI, some more beam plots and there's some info about the filters,
https://proaudiosales.hibino.co.jp/akg/49.html

[Gus]

Another link Another site along with the Royer Tape OP that seem to get the web DIY microphone stuff going in the 2000s IIRC
http://www.gyraf.dk/gy_pd/g7/gic.htm

Groupdiy microphone metas have links to schematics and articles some DIY microphone build article. Look at the metas for links
There is a microphone section. This site also has links and threads for building different circuits. IMO they are not clones unless they have the correct capsule grill and acoustic environment as well as other parts.

There was a Yahoo group that had good information. I believe it exists at another web site now

Neumann had a good PDF "Microphones" you could download, not sure if it is still available.

Then there is the Tape Op Royer DIY tube circuits into a MXL2001 and MXL603 like bodies

You can search the web for microphone schematics, kits, bodies etc. There is a lot of information you can find with a web search. There is good information and some not so good information. You can now find parts that were hard to purchase in the 2000s when I started building/adjusting tube and solid state microphones.

[Gus]

I'm an acoustic physicist and routinely work with equivalent circuits as mentioned earlier. All of your directivity patterns are based on the equation a+b cos(theta), if I recall off the top of my healthy properly. Basically it is a linear combination of two diaphragms with a phase. Figure eight is a=0, b=1. Omni is a=1, b=0. Cardioid is a=0.5, b=0.5.

Best resource is Acoustics by Beranek, but expect plenty of math.

Filtering will be done electronically. AKG C414 is my second favorite mic ever.

Shure has a good paper about capsule patterns I am looking for the link.

EDIT found the link https://www.shure.com/damfiles/default/global/documents/publications/en/performance-production/us_pro_dual_diaphragm_paper_ea.pdf-ff7e23c323c72be3deac4ffd742c1d26.pdf

good link https://groups.io/g/MicBuilders

another Shure link https://service.shure.com/s/article/how-to-test-phantom-power-voltage-and-current?language=en_US

[Jhalvers]

EEVBlog did a series with Doug Ford you may be interested in:
https://www.youtube.com/watch?v=ihAG6cMpUlY

[amptramp]

I have a Conneaut Audio Devices E-200 studio microphone that I picked up years ago at a garage sale for $10.  It has omnidirectional, cardioid and figure 8 patterns selectable by a switch.  There are two microphone (probably electret) capsules inside facing in the opposite direction.  With the back capsule output disconnected, you get a cardioid pattern.  With the two outputs added together in phase, you get omni.  With the rear element in opposite phase to the front, you get the figure 8 pattern.

I was told this microphone would have been $250 new and it is operated from internal 9 VDC Ni Cd batteries that can be charged by phantom power.

[Rob Strand]

There are two microphone (probably electret) capsules inside facing in the opposite direction.  With the back capsule output disconnected, you get a cardioid pattern.  With the two outputs added together in phase, you get omni.  With the rear element in opposite phase to the front, you get the figure 8 pattern.

For that to work each element must be a cardioid  (won't work with an omni electret.)


Those CAD mics use a simple charge pump for the capsule supply, see bottom right,

http://recordinghacks.com/images/mic_extras/cad/E300-schematic.png

I guess that could be an easier-to-build alternative to the transformer based converter.