musix2000

ELA M250e clone, an experimental prototype ... New
« on: July 23, 2020, 11:40:42 PM »
Hi ....
In the last years I`ve got a lot of information out of this forum and now I think it`s time to show you my experimental prototype. I`ve finished the build in the last month. The body and some parts of the psu came from a t.bone SCT-2000.
To find out what differences in sound various kinds of resistors and capacitors bring: I used switches for 3 different plate resistors and dip-switches for 5 cathode resistors and 5 bypass capacitors. Also there is a switch for two 100pf capacitors, one on or both off. One is an old ceramic tube capacitor, same kind as in the original M250e, the other a KP.
Outside is a switch for omni and cardioid. All switches are slider-switches with very low resistance.
The components inside are the best I`d found (my opinion): CT12 capsule by Tim Campbell, CM13114 transformer by cinemag, microphone graded GE 6072a tube from the 70ies and the best available resistors and capacitors, some NOS (Siemens karbowid), some modern (Vishay foil RS92NA, Welwyn RC55Y, and others). All grounded to one point.
Because nobody produces a suitable 8M resistor I`d asked vishay and they made some probes of the 7M96 cmf55-143 non magnetic for me (all=8M, less than 0,5%).
The components don`t touch the pcb or each other. The transformer lies on felt and is held by a thick wire with small silicon-dampers on it. The tube hangs on two rubber-dampers. Only the big 1uf partly touches the pcb.
The capsule is mounted on a rubber-damper which is mounted on a thick piece of plastic that is hold by four silicon-dampers (these once held the original SCT-2000 capsule). 

Maybe someone likes my prototype.
Here you can find some pics:
https://drive.google.com/drive/folders/1jJ0XkZHOZco51QeiIv9Ixl3MyO3B_nmv?usp=sharing

With a click on one of the tumpnails you can open the photos (= better quality).
PS: My english is not the best, please ignore faults I possibly made in the script!
« Last Edit: July 28, 2020, 11:49:24 PM by musix2000 »


Khron

Re: ELA M250e clone, an experimental prototype ...
« Reply #1 on: July 24, 2020, 09:20:46 AM »
And the exact value of that 8meg resistor was important because..?  ???
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ubxf

Re: ELA M250e clone, an experimental prototype ...
« Reply #2 on: July 24, 2020, 02:13:40 PM »
Nice work, did you find a setting you liked better ?

Re: ELA M250e clone, an experimental prototype ...
« Reply #3 on: July 24, 2020, 07:07:06 PM »
Congrats! However i have to do a bit of party breaking. Headbasket is largest contributor to a certain sound after the capsule. It affects the sound way more than most switchable components you have in there. This body has that bar right in front of the capsule, and both larger and further surfaces inside that cause ripples at different frequencies compared to the original. I have measured this, as i tried Tim's capsule inside that body. I don't doubt it sounds great though.
« Last Edit: July 24, 2020, 07:34:59 PM by kingkorg »

musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #4 on: July 25, 2020, 03:14:42 AM »
And the exact value of that 8meg resistor was important because..?  ???
Because it`s in the original schematics.

musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #5 on: July 25, 2020, 03:24:51 AM »
Nice work, did you find a setting you liked better ?
I`ve just finished it and can`t say much about differences. Some will be very subtile, others good to hear. I will find it out in the next month.

musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #6 on: July 25, 2020, 04:28:50 AM »
Congrats! However i have to do a bit of party breaking. Headbasket is largest contributor to a certain sound after the capsule. It affects the sound way more than most switchable components you have in there. This body has that bar right in front of the capsule, and both larger and further surfaces inside that cause ripples at different frequencies compared to the original. I have measured this, as i tried Tim's capsule inside that body. I don't doubt it sounds great though.
<"However i have to do a bit of party breaking"> Criticism is always welcome, I`m not an expert and still (for the rest of my life) in the process of learning.
I`m sure it`s right what you say. The headbasket plays an important role and each body with it`s inside has an effect to the sound. This microphone is only a prototype for me to learn, it`s not a final version. I`ve bought different sorts of mesh to find the best combination for this headbasket, but still haven`t done. I would prefer to use no mesh, each mesh is a filter for the incoming signal. I think most of the the C12 sound "airy" because there is only a minimum of mesh. But the capsule needs a shield, so the mesh is a must.
To minimize reflections I`ve put some cottontape inside the wall of the body. I don`t know if this mike will ever sound the same as the originals, but I try to come to their level as close as possible. Next step is a psu with Rosenthal carbon precision resistors from the 50/60ies. When I´m experienced enought I will build a final version of this mike.
<"This body has that bar right in front of the capsule>  In front of the capsule is no bar. Do you mean the horizontal bar on the upper side of the headbasket?? It`s some millimeters above the capsule.
« Last Edit: July 25, 2020, 06:30:35 AM by musix2000 »

Re: ELA M250e clone, an experimental prototype ...
« Reply #7 on: July 25, 2020, 07:08:12 PM »
Yes, that is the bar i am talking about. I have made a lot of ''custom'' headbaskets to avoid reflections, and made some truly transparent ones, but all of them were ugly looking at the end. I experimented with some conductive fabric which acted as pop filters at the same time, so there's an idea.

I even thought about building Faraday cage around my iso booth, but i never got that far. However i don't think it would make world of a difference in a real world situation.

You can also build a fet mic, with fet close to the capsule, inside the headbasket, this way you can run longer wires from the capsule (actually the fet) to the body, which will create less reflections and remain quiet. Something like AKG C1000 which has fet inside the capsule. It can be a SMD variant too.


musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #8 on: July 25, 2020, 08:01:01 PM »
Kingkorg, can you post a photo of one of your favorite "custom" headbaskets? Maybe we can find a way to make them looking good. I can learn from it and it would shorten the time of my experiments with different sorts of mesh and headbaskets (without a bar in the front ;)).
« Last Edit: July 25, 2020, 08:05:44 PM by musix2000 »

Re: ELA M250e clone, an experimental prototype ...
« Reply #9 on: July 26, 2020, 06:21:36 PM »
This is one of the options.


musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #10 on: July 26, 2020, 06:48:34 PM »
This is one of the options.
Thank you!!
Looks like 8 Mesh outside and 20 Mesh inside. Is this right?

Re: ELA M250e clone, an experimental prototype ...
« Reply #11 on: July 26, 2020, 08:41:26 PM »
I have no idea to be honest. Just tested until it worked. The foam under the capsule is like the foam used for 3M's yellow earplugs.

Or if you want to go crazy, it can be done without any headbasket. Capsule backplate has to be grounded, and diaphragm polarized. Cardioid only. Shielded cable from capsule to fet.
I wouldn't recommend Tim's capsule for this though.  ;D
« Last Edit: July 26, 2020, 11:13:49 PM by kingkorg »

musix2000

Re: ELA M250e clone, an experimental prototype ...
« Reply #12 on: July 28, 2020, 07:12:31 PM »
Or if you want to go crazy, it can be done without any headbasket. Capsule backplate has to be grounded, and diaphragm polarized. Cardioid only. Shielded cable from capsule to fet.
I wouldn't recommend Tim's capsule for this though.  ;D
Crazy, but I think it`s a good idea. With a little modification: the 2nd layer as a small cage very close to the capsule but isolated from it (and grounded), and the first layer of strong mesh mounted as usual (without a bar on front and backside ...).
« Last Edit: July 28, 2020, 07:20:14 PM by musix2000 »


 

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