Making some mics - Beginner suggestions

Hey all,

Its been almost a year since I last was active here. I had a lot of personal stuff that kept me offline for long.
Hoping most of it is behind me now, I am looking to get back into the swing of things.

I'm still very much a beginner, with little to no experience, but I want to get into making my own mics. I have several (cheaper) unused capsules and a ton of components and donor bodies lying around, so I just want to get in there and make some mics out of it. I like to stress that my goal (right now) is to learn, makes lots of mistakes, mess things up - I just want to end up with a working mic. I am not looking for top of the bill audio perfection in any way at this moment.


So my first question to you: What would be one or two great mics to build for me, preferably designs that have ready-made PCBs available and where I could use one of my existing capsules. It could be transformer output, or transformerless (I have those components). I assume I will need to still buy some missing components, that's alright.

Second question: I posted pics of my unused capsules below. Ordered well over a year ago I honestly can't remember what is what. One of them is a cheap Ali Express purchase, the other might be one from an Alctron mic. How can I tell what type of capsules they are? The one with the black tape is from my first build: a Microphone-Parts.com kit and its listed as a "double-backplate" capsule. Judging from looks, the others are also double backplate? Other differences I see is that the MP is edge terminated, the others are center terminated, with one having a screw on both sides, the other is missing a screw on one side? Or is this intentional? I am not sure yet how to interpret a capsule design.

Ali Express Capsule?


Alctron Capsule?



MP kit T12

Maybe something based loosely on a U47 or Tele Elam 251, there both fairly basic circuits ,no need to get too hung up on trying to replicate things exactly ,most likely a tube suitable for this class of service properly biased and you'll  end up with something better than you have already. You could try a wire ended sub mini tube and its easy to get good insulation resistance across the input, or a noval 9 pin (maybe EF86 triode connected ) and a ptfe base .

Picture 1 is no doubt a generic Chinese capsule.
Picture 2 and 3 look like an Alctron capsule to me.
Picture 4 is also a Chinese capsule, but with 'Quality Control' (which makes it a couple of times more expensive...)
It is normal to have no screw on the back of a single sided (cardiod) capsule, because there is simply nothing to connect to...

Ok thanks Guys for the great answers. I ordered a U87 circuit from vintagemics Dan so I think I will start with that. Since its my first time I dont mind blowing a few things up in the process

The chances that you will 'blow up' something, are very low.
If something is wrong, a circuit usually won't work at all, or it won't work as expected.
But to really  'blow up' something, you have to put in a lot of effort! 

I know Ruud I was only joking

As a side question while I wait for parts to arrive: what is an inexpensive tone generator for fet biasing? Maybe a diy kit out there that gives me some more practice soldering? My scope diy kit failed but at $8 its not a problem haha

A computer / laptop, a cheapo USB interface and something like Audacity?

Hi Krohn

I have all of that, but how can I feed a tone from the interface To the mic circuit? Unfamiliar with that

Thanks!

A connector (depending on what outputs the interface has - 1/4" jack, RCA etc), a piece of wire, possibly a pad (resistive divider / attenuator), and maybe a coupling (ie. DC-blocking) cap. Not exactly what one might call "rocket surgery"

Hey everyone,

So life happened. And another year passed where I had to set aside my mic project.
I'm gonna try and pick up where I left off lol. Hoping for better luck now.

So to recap, I first built a microphoneparts.com T12 with a friend who's experienced in electronics. I loved doing it and want to try it myself and learn along the way. I can fall back on him, for when things get hairy.

I have several parts already, but I realize now that they may not go together.

• I have the U87 green tapered pcb from VintageMicrophonePCBs
• I have a G47 6.5:1 Transformer from 3Uaudio
• I have various capsules and several mic donor bodies

So, my plan was to try and build the U87 clone and ordered the PCB's. I ordered the transformer over a year ago, and I now realize this may not be the right one for the U87, but rather for another mic build?  Since I have not ordered my BOM materials yet, I could potentially order a set of different PCB's for a different mic build, given that one of my capsules works with that.  You can see what capsules I have, from the photo's posted earlier.  I am a beginner, but I *think* I have:

• a alctron, single sided capsule?
  
• a chinese, double-sided capsule, double backplate? center terminated.
• the last one posted was the Microphoneparts build and capsule

I think the capsule with the white plastic rim might be the most suitable of the bunch? For purposes of learning, I don't want to invest in more expensive capsules right now. Unless really needed.

Some issues questions:

• What would be the easiest build given what I have right now?
• I fear my current donor bodies might not fit the PCBs + The transformer + Switches PCB. Is there a European friendly mic body kit I can get? the Studio939 shipping is $60 to where I live
• How can I see what is a single backplate and double backplate capsule?
• Does it matter if one is center or edge terminated? Only sound difference or also requires a different schematic/electronics?
• I don't understand the difference between a single/double diaphragm and single/double backplate? And why don't I read about a double "front" plate? I am really not grasping this

God help me. And maybe you guys

Thanks!

Chris

Hey Chris,

I know what it feels like to have a project sit for a year! Im glad you're getting back to it!

I think the easiest build you could do right now with the parts you have is Dany's u87 build. You can use the double sided isolated backplate capsule you have. The transformer you have will work but is not the ratio that the u87 calls for (9 or 10:1) as the one you have is 6.5 to 1. It will change the output gain of the mic but it will still pass signal and if you want to replace it in the future it will not be too difficult to swap them out. And you can swap the capsule with out much issue either if you want to in the future.

As for the mic body kit in europe... i have no idea as i am in the USA. You could try getting a behringer B2 off of ebay. I think the tapered kit fits in that microphone AND it has the switch slots (maybe you can even use that switch assembly)... not sure if those are readily available in the UK. ..but its a start

A double sided capsule means that the front and back of the capsule have diaphragms that are sputtered with gold and both sides can be used as a transducer for your mic circuit. Single sided capsules sometimes still have two diaphragms but the back side is usually an acoustic damper that gives you the sound of just cardioid of a double sided capsule... the back side of these still has the machined holes and the diaphragm but no gold sputtering and usually no wire as this is not useful in the circuit, just as an acoustic part of the capsule.

A double backplate capsule such as the ck12, k87 and k67 have two isolated backplates machined from different pieces of brass and separated by some insulating material. If you put a multi meter on each of the backplates you would not find continuity. If doubleThese will have 4 wires, one for each of the two backplates, and one of each of the two diaphragms. Example of double backplate capsule: (https://cdn.shopify.com/s/files/1/0867/8438/products/a_rk87_turn.jpg)

In single backplate capsules such as the M7 and K47 you can see a single machined brass piece behind the diaphragms. On these capsules you will find Example of an m7 style capsule from the side: (https://cdn.shopify.com/s/files/1/0867/8438/products/RK7LE-side.jpg)

As far as I understand, a center terminated capsule will function in a circuit designed for edge terminated capsules and visa-versa. I use a cheap single sided center terminated capsule I got off of eBay to test fresh mic circuits before putting in a fancy capsule. The mic still sounds pleasant and useful even with the cheap capsule.

I just did a D-u87 build with a genuine Neumann capsule. Sounds amazing... One tip with that build: make sure to get a good FET from a trusted source. I banged my head against the wall many times trying to troubleshoot my "faulty" circuit right after the build... turned out the FETs i got off of eBay were convincingly faked chinese FETs that were repainted with the fairchild logo and part number. Gahhh whyyyy!!!!!???? So, just get the good ones and you'll thank yourself later.

Oh, and wear gloves when handling the capsule and the HiZ section components. For good measure i just always wear gloves as i'm working on the insides of the mic.  Another tip is to get some no-clean solder for at least the high Z section of the mic... Keep it clean and it would be noise free!

If you want to try your hand at a tube microphone in the future I would suggest the DEF47 with the ef800 tube. It was a pretty straight forward build and you could get the microphone body from Aputis who has plating reject bodies that are mechanically perfect. He is in Europe... Latvia i think. I used a genuine Neumann capsule. If you buy a kk47fet capsule you can save hundreds of dollars. It is mechanically identical to the k49 capsule but the front and back capsules were too far out of tolerance for neumann's standards. But they are such tight QC standards that it really doesn't make too much of a difference. Just put a wire on the back capsule and you essentially have a k49 capsule for hundreds of dollars less. Tangent..... Anyway, that microphone sounds amazing.

Hope some of that was helpful. Happy Building!

Best,
Eric

hi Eric,

Thanks SO much for the great in-depth answers. That is very helpful, I appreciate it.

If I understand correctly, could I say if the brass part has the "screw holes" in it (whether or not it comes with a wire already attached or not) it counts as a "plate"? Aside from seeing a seam where two brass parts join, I am looking for other ways to visually tell them apart.

Now I like to think I understand how a capsule works, the vibrations on the diaphragm are converted to an electric signal that travels down the wire. That signal is boosted/amplified to make it audible/consistent. Right? So what is the function of having two backplates? Does this mean there are also two diaphragms? Three diaphragms in total with the front included? Or does a double backplate only have one diaphragm? I am not really clear what the double-backplate does instead of a single one, and why the same function would not be used on the front. 

Ok so based on your reply I am pretty much settling on doing the u87 build. Looks like a lot of fun. I understand that the trafo will result in a lower gain, and maybe a different sound because of the way it "drives" the circuit?  Im fine with ordering a diff. transformer if needed. I will also look for that Behringer mic/body. If all fails, Im gonna order the Studio939 stuff and just eat that $60 in shipping.

I've soldered a few Chinese mic DIY things to practice and those worked. I think I might struggle a bit with the tiniest of solder joints, but otherwise, I think I'm gonna be ok in this department.  What I don't know how to use is a multi-meter, this is black magic for me at this stage. Reading about things like biasing FETs is kinda worrying to me, but Im gonna cross that bridge when I get there.

Lastly, wearing gloves; sure gotcha. But what is the HiZ area?

Cheers!

Chris

Also, I was trying to order this BOM http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=1AD602D54E
But the website gives me an error with the 610-2N3819 RF JFET Transistors N-CH -25V 10mA
Is there a comparable component I can get that is not the 2.500 bulk pack? Im having a hard time figuring out which one is the correct one to order, since there are so many Fets.

I also have some Fets myself already, that look to be the same spec?
Would they do?

Cheers!

Chris