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adammurtomaa

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Mar 14, 2020
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2
Hey guys!

My name is Adam and I'm an audio engineering student at SAE Institute Berlin and I'm currently in my last semester of my Bachelor's Programme. I had made extensive plans for my Bachelor's project, which relied heavily on working with a bunch of other people, but thanks to the covid-19 epidemic, I was forced to change my Bachelor's project last minute to something more...isolated.

My new Bachelor's project is to build a microphone. Originally, I wanted to do just a straight forward clone and do some exact measurements and comparisons to originals, but I was informed that my project required some "creative" input or influence from me, so a 1:1 clone would not be "enough". I have to build something and mod it. The suggestions and ideas so far are to build:
- a U47 or C12 where I'd add something like a HPF or a pad to the PSU
- a U87 with some sort of customisation to the mic, like LPF or a simple tilt EQ
- a U87 in a completely different donor body, like a Røde Procaster and turn it into a top-address microphone

I wanted to post here and get some thoughts and opinions from this fantastic forum and see what you guys think of these ideas. I am brand new to the world of DIY microphones (but not brand new to DIY electronics), so I don't know which of these three is most easily accomplished or would be the most fun/interesting project. Maybe some of these ideas are silly and way too hard - I don't know! If anyone has any other fun ideas for me, I'd love to hear them.

Another factor that I feel is drastically important to factor into this is availability of parts and such. I've been looking around online for U87 kits and B.O.M.s and parts seem to be getting scarce. I'm hoping to have a solid idea ready within two weeks and hopefully start ordering parts as soon as possible.

I'd be immensely thankful if some of you geniuses here would be willing to help me out.

Note: anyone that contributes to the project  will absolutely get credit for doing so in my B.Sc. thesis.

Warmest regards,
Adam
 
You might like to take a look at my notes for this project :  www.amx.jp137.com  which came about as a result of a thread on this board ( see here:  https://groupdiy.com/index.php?topic=71586.0  )

Not perhaps exactly what you're looking for, but with only Sennheiser and Rode  using the concept commercially, there's plenty of scope for experimentation in this area ....
That might allow you to come up with something more original than a conventional mic 'clone' for your B.Sc thesis? 
 
+1 for the RF-microphone approach if you want to go a route less traveled. There are interesting possibilities in there, I think.

Alternatively, perhaps:

..what about looking into external mechano-acoustical equalizers / resonance chambers as physical "plug-in" equalization by bringing them close to the microphone membrane? Like a positive usage and control of  extended headbasket-induced influence on sound pickup

..looking into what known tube specifications or parameters you would suspect/estimate to have the highest correlation with the tube's chance of sounding subjectively good in a condenser microphone..

Is your direction theoretical/practical/electronic/mathematical..? At approximately what level?

/Jakob E.
 
If I may, are you actually interested in microphone design?  By that I mean, the testing, circuit design, capsule design, acoustical impact from headshell/screens, etc.

I see you're in audio engineering school.  I am a musician who gets better gear than I could afford by just buying by rolling my own.  So I only really care about microphone design in that it gets to the end goal of something usable.  I'm personally happy ordering good parts and building a clone, and know enough to get one working, biased up and in the mic closet.  Other people here don't even play or record and are just super into designing microphones and building better mousetraps - no judgement, those guys are the ones that give musicians our tools to make records, and design the stuff us copy guys end up copying!


If you fall into the former camp, I would suggest doing something that will teach you the skills that will be most useful to you in your engineering career, which I think would be building some kind of preamp, EQ or compressor.

You could, for example, "Design" a tube preamp by picking one of many commonly used audio tubes, and deciding which one works for your application. 6922, 12ax7, 12au7, ef86, etc.  All of these are used in preamps for different reasons, and you could learn all about that.  Then you have the choice of input and output transformers, and deciding why to use each and what these do to the sound.  You can learn about impedance loading and the impact on frequency response.  If you put an EQ in the circuit, you can learn how to adjust the Q and frequency centers of the EQ points.

Anyways, I don't personally feel that you will learn that much, and the end result won't be as useful if you just try to hack a filter onto a u47 circuit.  Those circuits are classics for a reason - they work!  If you don't have the test gear and the interest in learning how to do those measurements...

The world needs another tube preamp design like it needs another (insert metaphor here) but at least with this, the knowledge will help your recording abilities.  Specifically the input and output impedance stuff, and how to build simple tube circuits.

Just a thought
 
Thanks for your feedback, guys! Very interesting points from you all.

rogs said:
You might like to take a look at my notes for this project :  www.amx.jp137.com  which came about as a result of a thread on this board ( see here:  https://groupdiy.com/index.php?topic=71586.0  )

That RF mic looks really interesting. I've gone through the entire website and it looks like a fun project. I've bookmarked it and will possibly do that as a final project, since it is definitely a road less travelled.

gyraf said:
..what about looking into external mechano-acoustical equalizers / resonance chambers as physical "plug-in" equalization by bringing them close to the microphone membrane? Like a positive usage and control of  extended headbasket-induced influence on sound pickup

That's a really nice idea. That allows me to make mods to the microphone without having to delve into electronics that I'm unfamiliar with. This sort of plays into my idea of looking into doing a top-address U87 (or similar).

Does anyone know where I could dig up specifications on the internal dimensions of something like a Røde Procaster? I've been Googling away, but get seem to find anything.

rockinrob86 said:
If I may, are you actually interested in microphone design?  By that I mean, the testing, circuit design, capsule design, acoustical impact from headshell/screens, etc.

In all honesty - I don't really know enough to be fully enamoured by the idea of circuit design, capsule design etc., but I am really interested in microphones and other recording technology. I'm a very "learn-by-doing" type of person, and a huge part of why I want to build a microphone is to learn/teach myself the internal workings of microphone parts. Learning this would also be a huge benefit for my career, as I'd love to be able to fix microphones and other gear in the future.

rockinrob86 said:
...I would suggest doing something that will teach you the skills that will be most useful to you in your engineering career, which I think would be building some kind of preamp, EQ or compressor.

You could, for example, "Design" a tube preamp by picking one of many commonly used audio tubes, and deciding which one works for your application. 6922, 12ax7, 12au7, ef86, etc.  All of these are used in preamps for different reasons, and you could learn all about that.  Then you have the choice of input and output transformers, and deciding why to use each and what these do to the sound.  You can learn about impedance loading and the impact on frequency response.  If you put an EQ in the circuit, you can learn how to adjust the Q and frequency centers of the EQ points.

Another really good idea. I've given some thought into possibly building something else, like an EQ, compressor or a pre-amp. Maybe I'd be better off with building a pre. The only thing with building a pre that has me a bit hesitant is the fact that I doubt it'll be a good investment, since I don't really foresee I can design and build a tube pre that's going to be good enough to out-perform or even compete with store-bought pre's. You know what I mean?

I greatly appreciate the input from you guys. It's highly valuable to me. Thank you for taking the time.

- Adam
 
I've built a bunch of mics, and still don't really know how they work.  I get it generally, but if you're building a kit...It's not like you're plotting out, measuring and testing stuff when you build a "U47".  You look at the schematic, build it, and it works.

A tube preamp (maybe this is to me because I've worked on tube guitar amps and stereos a bunch) is an easier thing to get your head around designing, and then you have a way better understanding of gear in general.

preamps have an input transformer, an amplifier stage, the volume pot, usually another amplifier stage, or maybe an eq stage, and then maybe a final amplification stage that feeds an output transformer.  The whole thing needs a power supply. 

What is great, is all of these circuits are easy to find online, if you look for the normal tubes and define the application for it.  You can compare differences between RCA BA pres, EMI Redd47 and something modern like the G9.  Very interesting!
 
The mic build I learned the most from is an M49b. It's a challenging build for a first timer though.

A vari-mu comp would be another project that you could learn a lot from. Especially if you play with time constants; mod a classic design to add faster or slower time constants.
 

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