Beginner microphone building questions

[Duizels]

Hello,

The past weeks I've been lurking around here (and elsewhere) soaking up knowledge. I've been home recording for years and recently built a first DIY mic kit. It has gotten my super excited about the subject and I love to learn more, build more own mics.

But I'm blessed with a creative brain (I paint and design) and maths is like dyslexia for me. My knowledge of electricity is zero. I've started reading books like this but it quickly gets too complex or mathematical for me https://www.ibiblio.org/kuphaldt/electricCircuits/  I've read somewhere here that its never too late to learn so here goes. I like to understand this and learn...

I wanted to post some questions here, and get a thread going to give me a basic understanding of how everything works in a condenser microphone, so when I eventually build another mic (kit or self) that I can understand what I am doing, instead of "paint by numbers"... I appreciate your time for helping me come to grips with this materials!

My first questions are based around the T12 kit from microphone parts, based on the Neumann KM84 circuit. The signal path is described as JFET > Output Cap > Transformer.

So if I understand correctly, phantom power is sent from the XLR pins (which ones?) through the circuit, to put a constant charge on the capsule. Sound pressure makes the membrane move, causing a varying voltage sent out from the capsule. The first "station" now is the JFET correct? From what I have read the JFET sounds like being a "gate or valve" allowing more or less voltage to go through? But what is its function? Because the diaphragm already sends varying voltage out?

The next stage is the Output Cap. From what I read online this serves the purpose of "filtering", allowing sound? to move through but not DC?  I read it removes noise? My lack of electricity/audio understanding really makes this hard to grasp. This component also colors the sound? I read that depending on the material it gives clean or warm/thin/colored transfer of the sound.

The last in the signal chain is the Transformer. Is this simply to boost up the incoming signal to a "loud" enough source to record? Or is its function different? Again I also read that this part heavily influences the sound of a microphone?

Because of my lack of understanding of electricity, I am confused about what is Voltage, Current and DC? And which is of these is the "sound" and which is not?   When I read things like "this part blocks DC" to me it pictures in my mind like different streams of water, the electricity (DC?) is blocked but the sound is allowed to pass through ? Probably I am getting this TOTALLY wrong haha I feel such a n00b.

regards!

 

[Khron]

At least according to the industry standard, phantom-power is supplied through a pair of (ideally, matched) 6.8kohm resistors (within the preamp) to both pins 2 and 3, and using pin 1 as the ground return.

The role of the JFET is an impedance adapter. Yes, there's some voltage coming from the capsule, but it can only supply a reeeeeeeeeeeeally really tiny amount of current (nowhere near enough to drive the ~1-2kohm input impedance of most mic preamps). JFETs have really high input impedances (giga/teraohms), so the minute current the capsule can supply is more than enough to drive them.

A capacitor in series with a circuit forms, for the most part, a high-pass filter (as in, it only allows HIGH frequencies to PASS - get it? ). DC is basically 0Hz, so that gets blocked off from the definition. The audio signal is AC and, unless the value (nF/uF) of the cap is way lower than it should be, it passes right through. The lower the frequency though, the more it is attenuated. And yes, at least up to a point, various dielectric (insulating) materials used in cap constructions can affect the signal passing through.

Actually, in microphones, transformers are used to attenuate the signal and, in the process, adapt the high Kohm-range impedance of the signal coming out of the JFET or tube/valve to a lower tens/hundreds-of-ohms-range impedance. This is so the signal will be less affected by the (length of) cable and the preamp input impedance.

Voltage, at least by the book, is the difference of potential between two points ;D Current is the (amount of) flow of electrons. DC = direct current = most often than not, the supply voltage for a circuit, or any voltage that is, under normal circumstances, non-variable.

Actually, if you wanna go the route of the water analogy, voltage = pressure and current = flow rate.

Don't sweat it Noone was born fully-documented in this field, we all started SOMEwhere And as the old saying goes - the only stupid questions are the ones that remain unasked

 

[micaddict]

Welcome, Duizels!

Seems like new member week here. 
Where are you from if I may ask?

I like your first post and your honesty.
Hey, maybe this thread can become a sticky for future newbies who start from scratch.
With everything explained, step by step.

BTW, it's called dyscalculia and yes, some great creative minds or artistst have/had it.
And some think they have it, but eventually surprise themselves. 

 

[homero.leal]

Hi  Duizels,

I would recommend you to have a deep dive into Henry's Audioimprov.com site, at the mic section.

http://www.audioimprov.com/AudioImprov/Mics/Mics.html

He has a lot of great information on mics design, building, modifying and more. It was one of my favorite starting points on the DIY mic building world.

Take a look, you will love it!

HL

 

[Khron]

I've pointed people to that site myself a few times Although i'd rather add the link straight to the "archive" page, for the full list of his articles on the topic:

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

Hi  Duizels,

I would recommend you to have a deep dive into Henry's Audioimprov.com site, at the mic section.

http://www.audioimprov.com/AudioImprov/Mics/Mics.html

He has a lot of great information on mics design, building, modifying and more. It was one of my favorite starting points on the DIY mic building world.

Take a look, you will love it!

HL

 

[micaddict]

Yes, nice site. 

But would it hurt to have something like that in our own home? 
Like a dedicated thread for microphone build beginners.
This one could be it.

 

[ln76d]

From what i remeber it's called Microphone META

 

[Duizels]

Where are you from if I may ask?

I like your first post and your honesty.

I am also from the Netherlands, like you I see.
Thanks for the warm welcome.

I think from what I've read so far I mostly understand what certain components do because of experience with recording/mixing gear. I mean LPF, HPF, roll off, thresholds etc. that  is stuff I understand fine. I think I struggle the most with the low level of how electricity works, and how "audio" is transported/or "a part of" electricity. That's why the whole AC and DC confuses me. Are there "2" things happening at once in 1 electric current? Or is it one and the same thing? I can't find a good explanation anywhere that explains this. They all sort of jump to the assumption that you "know" that part.

 

[Duizels]

I would recommend you to have a deep dive into Henry's Audioimprov.com site, at the mic section.

http://www.audioimprov.com/AudioImprov/Mics/Mics.html

Ok thank you that will make a perfect evening read. Thanks!

 

[ln76d]

The best way to learn theory is the practice.
Find the final circuit which you want to build and then would be easier to explain things
You can for the start find some microphone to mod - it's gret for start

 

[micaddict]

I am also from the Netherlands, like you I see.

Ik had al zo'n vermoeden, Duizels. 



Henk

 

[Duizels]

The role of the JFET is an impedance adapter. Yes, there's some voltage coming from the capsule, but it can only supply a reeeeeeeeeeeeally really tiny amount of current (nowhere near enough to drive the ~1-2kohm input impedance of most mic preamps). JFETs have really high input impedances (giga/teraohms), so the minute current the capsule can supply is more than enough to drive them.

Ok, so the JFET is super "easy" to trigger by tiny currents, so that is the reason it is used in combination with a diaphragm capsule? Because the tiny signal coming from that would not be enough for other amps to work with? But if this is the case, how are there also large diaphragm mics that do not use JFET ?  How do they translate the signal coming from the capsule into a "boosted" signal?  Also is a JEFT making the signal louder? if so how does it do this? Because from the videos I watched on JFET it looked more like it was "squeezing/limiting" its interior channel, suggesting "less" gets through?

A capacitor in series with a circuit forms, for the most part, a high-pass filter (as in, it only allows HIGH frequencies to PASS - get it? ). DC is basically 0Hz, so that gets blocked off from the definition. The audio signal is AC and, unless the value (nF/uF) of the cap is way lower than it should be, it passes right through. The lower the frequency though, the more it is attenuated. And yes, at least up to a point, various dielectric (insulating) materials used in cap constructions can affect the signal passing through.

Ok so it blocks the 0Hz DC current, but why? Why is it necessary that this part is removed? And why at this point and not earlier? I guess the DC is needed to keep the circuit working continuously, but if after the Cap and Transformer the direct current is removed, what happens there? Is the electricity gone or is AC also electricity? I feel such a n00b

Actually, in microphones, transformers are used to attenuate the signal and, in the process, adapt the high Kohm-range impedance of the signal coming out of the JFET or tube/valve to a lower tens/hundreds-of-ohms-range impedance. This is so the signal will be less affected by the (length of) cable and the preamp input impedance.

So, its not needed to have a transformer there, using modern pre amps/audio interfaces?
Or is it just an allround smarter choice to do it?  Also, in what amount does this "color" or "detail" the sound? I've read TONS of talk about Cinemag, Telefunken, BV-8's and what not suggesting (and guessing by price-tag) that this is critical to the sound. A friend told me poor quality laminated transformers have a sort of internal "bleed" or "jumping over" of electrons causing noise or a less clear sound. Is that how it works? 

 

[Duizels]

The best way to learn theory is the practice.
Find the final circuit which you want to build and then would be easier to explain things
You can for the start find some microphone to mod - it's gret for start

I will for sure. I can't wait to build a microphone from one of the classic schematics in one of old bodies I have lying around.
But having never worked with electronics before, never soldered and I have none of the equipment yet, I don't want to short circuit myself and found dead next to my desk in the morning I might try and start with some absolute beginner stuff to familiarize myself.

 

[ln76d]

Fet microphones don't kill people - tube microphoens kill people - try to rap this ;D

It's nothing complicated - look for "kit" threads - some people there build their microphones like  a monkeys with the blocks.
Some have no idea what they are doing but "it work". There's also o dozen of question - "which capacitor should go there... " and a lot of things which keeps me mostly away of reading these topics.
You are in better position

What you need for a start is:

-soldering station
-tin (PB - not any sh*tty rohs lead free)
-solder sucker
-clean isopropyl alcohol (no, not for celebration of finished project) - for cleaning PCB.
-brush to clean boards
-open mind
-at least multimeter

 

[Duizels]

I am also from the Netherlands, like you I see.

Ik had al zo'n vermoeden, Duizels. 

Not many people know Duizel, its about as small a town as it gets. Less than 1.000 inhabitants

 

[homero.leal]

Another suggestion, try Scott Helmke's Alice Microphone first

http://www.scotthelmke.com/alice-mic.html

with the original design and components as suggested by Scott.  It's a  very simple and straightforward design.

Will be a great and rewarding experience having a bunch of electronic components transformed into a nice sounding mic.  That was my case...

After that, you could move to more fancy and complex designs.

Regards!

 

[Potato Cakes]

The kits from microphone-parts are great and have very clear instructions. Even if you don't exactly get what is going on electronically, you should, with some patience and double checking, be able to build a microphone that will sound really nice. If it's your first mic build, I would recommend this route.


Thanks!

Paul

 

[ln76d]

Good idea, but i think it would be even better to know how it work. Or maybe not? Maybe is better to be monkey - blocks - kit builder?

 

[Potato Cakes]

Absolutely, I agree it is best to know how these things we build work. If one has some success early on in this great DIY adventure, it would create motivation to keep learning.

Thanks!

Paul

 

[ding]

http://groupdiy.com/index.php?topic=61057.0

Cheap and easy except the biasing part but whatever, biasing is not the end of the world.