OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87

[micolas]

Cheap capsules produce harsh high frequencies that cannot be leveled with a transformer, and some capsules even remove the high frequencies altogether.

Not all cheap capsules have the same FR. On the contrary, there is a large dispersion of parameters. So we don't generalize, some cheap capsules have a pretty good FR shape in the 3-5kHz area where sibilance, harsh etc. are produced more frequently (which depend on the sound sources, voices), but they only have exaggerations in the higher highs. Let's just mention the 797 and Takstar capsules, which have more air than the Neumann.
I use with good results some Chinese transformers in the 87 topology, through a steeper Deemphasis only in the upper trebles.
Example: cts-2 from p420
@kingkorg 's research confirms the ATK measurements I have high confidence in.

 

[Juan Vargas]

Recently received the boards that I ordered from Chinese comrades here:
https://aliexpress.ru/item/10050075...l.0.0.1ace4aa66dWHla&sku_id=12000041381203745
Excellent quality of manufacture! This is not an advertisement.
And once again many thanks to comrade Juan Vargas for providing the Gerber files!
Now I will wait for a scattering of separately ordered parts to begin assembly. I will definitely report the results here.

amazing Korablev hey the pads for the transformer wires I just notice that on my PCB might be a little small is ok I also order one more time the boards for the other mic body I place temporally the PCB to the other body with zip ties and it doesn't look that bad at all

 

[Juan Vargas]

hi guys is about R7 the 1GΩ I was reading throughout this section ORS 87 and OneRoomStudio mention that R7 doesn't need to be exactly 1GΩ one just of a hundred of MΩ, a 500MΩ will do?

 

[Voyager10]

It will work, the main difference will be more low-frequency noise from the circuit.

 

[micolas]

@Juan Vargas
Why don't you try to find out for yourself? Test different values. Put 2Gogm or other values.
If experiments don't make you happy, then it's cheaper just to read different threads.

 

[Juan Vargas]

@Juan Vargas
Why don't you try to find out for yourself? Test different values. Put 2Gogm or other values.
If experiments don't make you happy, then it's cheaper just to read different threads.

thanks micolas I will do just that, experiment using this resistor is a 1 G Ohms

 

[micolas]

thanks micolas I will do just that, experiment using this resistor is a 1 G Ohms

¡Sí, señor!
That's the DIY spirit. Experiment as much as you can and enjoy!

 

[Khron]

thanks micolas I will do just that, experiment using this resistor is a 1 G Ohms

I just hope those humongous things fit inside that mic body...

 

[micolas]

@Khron the observation is good
That Murata resistor is a bit big physically: 23.5x9x2[mm], 1.6watts, 10kV.
But if it's the only one you have on hand quickly, it will work fine.A solution will be found
I bought 1G resistors of very low power, cheap and they work well.

 

[Khron]

TE Connectivity RGP0207 series are also half the price (or less?) of those big Murata ones

 

[micolas]

TE Connectivity RGP0207 series are also half the price (or less?) of those big Murata ones

+1
These are exactly what I use with excellent results! 0.25w
They have a small physical footprint, are cheap and readily available.

 

[Juan Vargas]

¡Sí, señor!
That's the DIY spirit. Experiment as much as you can and enjoy!

como sabias que hablo Español? = how did you know that I speak Spanish buen dia = good day

 

[micolas]

como sabias que hablo Español? = how did you know that I speak Spanish buen dia = good day

@Juan Vargas your username in GDIY is purely Asian
(I'm sorry, I couldn't help myself, I'm in an overly humorous mood sometimes!)
Well, I lived 4 years in Spain, in the south, in Puerto Lumbreras, on the border between Murcia and Almeria. I have many musician friends, I was a sound and technical engineer and sometimes a musician, live and in the studio.
Extraordinary, friendly, hospitable people who love life, good music, food, fun. We are Latinos
(Bueno, viví 4 años en España, en el sur, en Puerto Lumbreras, en la frontera entre Murcia y Almería. Tengo muchos amigos músicos, fui ingeniero de sonido y técnico y, a veces, músico. En vivo y en el estudio.
Gente extraordinaria, amable, hospitalaria, que ama la vida, la buena música, la comida, la diversión.
Somos latinos)

 

[Juan Vargas]

wepa! me alegra eso hermanito = I'm glad brother que bien! soy de Puerto Rico = I'm from Puerto Rico hey if you need any help with PCB design I can help maybe you already knows more than I do but I can help with ideas here cuidate hermanito = take care

 

[jp8]

+1
These are exactly what I use with excellent results! 0.25w
They have a small physical footprint, are cheap and readily available.

And for even more small, affordable 1G, 2G, 3G, 5G or even 10G resistors:

https://a.aliexpress.com/_Ez5ovqC

https://a.aliexpress.com/_Ey2mk9w

I use the first one for prototyping. The 2nd one is a potted version, which I assume is better and is the one I use for mics that will see some real use.

Jan

 

[mrchapp]

And for even more small, affordable 1G, 2G, 3G, 5G or even 10G resistors:

https://a.aliexpress.com/_Ez5ovqC

https://a.aliexpress.com/_Ey2mk9w

I use the first one for prototyping. The 2nd one is a potted version, which I assume is better and is the one I use for mics that will see some real use.

Jan

I'm intrigued -- Are those two options better than more typical resistors such as this (more expensive) one?: https://www.aliexpress.com/item/1005005953357537.html

 

[micolas]

wepa! me alegra eso hermanito = I'm glad brother que bien! soy de Puerto Rico = I'm from Puerto Rico hey if you need any help with PCB design I can help maybe you already knows more than I do but I can help with ideas here cuidate hermanito = take care

Ok bro! For now send me some warmth, in your country the temperature is 28° and here in Romania it is 7° below zero.
(¡Vale tio! Por ahora envíame un poco de calor, en tu tierra la temperatura es de 28° y aquí en Rumania es de 7° bajo cero.)

If I need help with pcbs I'll ask you, I'm an old DIY wolf who has no patience to make pcbs anymore, so I quickly experiment point-to-point in old school style, like I used to build when I was a teenager
And don't forget to have fun! I think that during this period you have festivals, fiestas

 

[micolas]

And for even more small, affordable 1G, 2G, 3G, 5G or even 10G resistors:

https://a.aliexpress.com/_Ez5ovqC

https://a.aliexpress.com/_Ey2mk9w

I use the first one for prototyping. The 2nd one is a potted version, which I assume is better and is the one I use for mics that will see some real use.

Jan

Many thanks Jan!
You are a gold mine!

 

[jp8]

I'm intrigued -- Are those two options better than more typical resistors such as this (more expensive) one?: https://www.aliexpress.com/item/1005005953357537.html

Good find! Didn't know those. So I haven't used them and have no clue whether they are any better. At least they are smaller, which can be beneficial in SDCs when mounted close to the board edge. Unfortunately, no 2G or 3G available, which are my preferred values to use in SDCs.

Talking about "better": how should we define "better" in the context of these GOhm resistors? They don't need to be accurate. Maybe low excess noise? Does anyone know? I was able to find references to excess noise measurements of other types of resistors, but not GOhm resistors.

Jan