6 years in the making

[MicDaddy]

This is not the first time hearing about different impedance coils.

Can anyone shed light on characteristics of coils regarding say a 60ohm version vs another?

There's not a lot of room in the air gap to make drastic changes to wire size or coil structure, or is there?

All of the dynamics I've worked on had only 1 type of coil and diaphragm. To deviate is to experiment and it sounds like AKG was ahead here making a product more versatile by which part was to be used in the structure of the capsule.

 

[ln76d]

D12, D20, D25 which i had were 200ohm and 60ohm.
Donor AKG microphones (even same model) had a lot of other impedances, 15ohm, 20ohm, 45ohm (if i remember correctly), 60ohm, 200ohm, 250ohm, 500ohm and probably something between.

 

[MicDaddy]

How much of this impedance change was handled at the transformer vs at the voice coil?

Are there visible differences between the coils, wire size, number of turns, etc?

 

[ln76d]

I only posted coils impednces, transformers are different pair of shoes.
D12 was availble also as 500ohm and Hi impedance via transformer.
Donors also had different transformers.
I didn't investigated coil wires thickness, all are pretty thin, looks like the same.
It looks like it's more wound wire for higher impedance.
You will not count number of turns, to thin.

 

[MicDaddy]

Counting the turns is the only way

 

[bryanday]

Actually, you can totally work it out with maths!

I created a spreadsheet that calculates the resistance (which will give you an idea of the impedance) of a coil, depending on the coil height (which, along with the wire thickness, will dictate the number of turns per layer) , wire thickness, number of layers, inner coil diameter (which then dictates the outer coil diameter and thus the clearance in the gap). The overall length of wire is derived from these figures and also used in the overall calculation.

The resistance of different wire thicknesses can easily be found on the web. I've measured the dimensions of the capsule magnets/gaps etc.

It's made using numbers on macOS, but I think it should load up into Xcel (does that even still exist?) or whatever you PC guys use.

Happy to share it if it's any use/interest to anyone. It's very easy to try different parameters and see how it affects the overall dimensions/impedance etc.  It shows that you can make an around 60ohm coil, 1.7mm high, using 4 layers (you need an even number in order for the tails to enter and leave the coil at the same side (top/bottom) of the coil.)  using 44awg (0.0508mm) wire, around 33.5 turns per layer. You can get around 0.15 mm clearance between the coil and the assembly using these parameters.

For around a 200ohm coil you need to use thinner wire - 47awg (0.03548mm). Still 4 layers, but you get around 50.7 turns per layer. You actually get more clearance between the coil and the capsule assemble using these parameters - around 0.2mm either side.

There are other factors to consider that I haven't yet incorporated (e.g. the extra thickness that might be added to the wire by the bonding layer on self-bonding magnet wire will slightly reduce the number of turns per layer and thus the overall length/resistance)

You get the idea, anyway... I'm waffling now..!

Bryan.

 

[MicDaddy]

Bryan can I try your spreadsheet on some known coils I have and see how close it comes?

We would still need to extract a lot of data from an existing coil(s)

If it works, seems it would save a loooooooot of time especially those dynamics which are direct coupled to the XLR sans transformer, many turns of frog hair.

 

[bryanday]

PM sent...

 

[bryanday]

Any thoughts on the spreadsheet? I'm so sick of trying to graft extension wires onto donor coils!!! Anyone got any tips on that front?

Bryan.

 

[bryanday]

Bump.

 

[Whoops]

Really interesting work, congrats in pursuing this challenge

 

[nashkato]

 

[Whoops]

Hello MicDaddy,
How is your quest for making D12 replacement Diaphragms?
Any progress lately?

I'm sure there will be a market for it since a lot of people have failed D12 mics in the mic locker and would love to use them again.

In writing "D12 repair" on google I was amazed by the number or threads and questions on the subject and by so many people trying to be able to resurrect their D12 mics.
Also the few D12 mics in the world that are still working properly will unfortunately  eventually fail also

 

[sr1200]

Hey i traded my D12 to a member a few years back. I would love to put something together that has a similar sound to it.  I recently got into 3D printing and have made a bunch of DIY parts (421 replacement clips, ribbon motor mounts, flanges, etc. ) if theres any plastic you need for proto purposes, let me know, be glad to help out.

 

[bryanday]

..... tumbleweed....    :'(

 

[Lucas Rosso]

Have been rolling coils for a few years now, was tough because we were starting with nothing much to go on. Luckily I had found a Renaissance man in a consulting-engineering/machinist who put me on the right path.

@ln76d, Are you looking into or maybe have it done 8) the shims for the D12?

Anyone know if Esa Tervala participates on this forum?

Dany Bouchard donated a D12 for me to try to copy. But I vaguely remember Esa telling me that the diaphragm had changed. I do not have any experience with these mics so I'm leaning on you guys for what to look for in an "ideal" dynamic.

i don't know if you already made it, but, if it's possible, i want to buy a membrane

i'm trying contact with chinese suppliers, waiting for the response

have a D12 with a torn membrane and smashed voice coil

 

[Whoops]

i don't know if you already made it, but, if it's possible, i want to buy a membrane

Last post of MicDaddy in this thread was 7 years ago...

He is still around in this forum, but by the lack of activity in this thread I think this idea was ditched in 2016

 

[MicDaddy]

CT scan the diaphragm(not cheap but if you can scale making them it can be economical,) send the SLDPRT to a capable machinist(super not cheap + good luck finding someone capable) to make a hot die clamshell and into the lab for time under temp and quenching science(yes this stuff matters(ha a pun!).) Have fun sourcing materials without ordering a semi-trailer full.
It's really that easy but I'm not pursuing it for the D12.
Stewart at Xaudiamics is the guy to ask, if anyone has made progress it'd be him or Esa Tervala. Oliver was rumor'd to have the tooling but I was never able to work with him in time.

Stewart is my best bet: Login • Instagram

I'm so backed up with RE20s I had to abandon this.

The voice coil is incredibly difficult until you know how, then it's really easy. I hired several PhD and highly capable engineers/machinists to tackle the tooling and it took many many attempts to get it right. In hindsight it now seems so simple but it took a lot of effort($$$) getting to that point.

If you do pursue this a helpful friend over there at Beyer Dynamic's service department is very open about helping with processes. BD voluntarily taught me more about the material science and processes of making diaphragms than the entirety of another unnamed engineering dept of which I have great respect for (and worked with for many years.)

If i can lend any help from my experience tooling up the RE20 coils and diaphragms I will to a point. It was tough finding people to help and I'm forever grateful to ALL who did in whatever role they played how large or small. If I can pass that forward I will, short of giving away the recipe for free(which I still may someday.....i kind of sprinkled a lot of it here already, it will still take much effort tho even with all the secret info )