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

[elskardio]

They are very small: Style TLM102
For U87, TLM103 style ones would be more suitable

https://a.aliexpress.com/_EzN5r6n

with this stripped down circuit, I don’t see the point of a bigger mic body!

I like the compact size of the 102.

 

[micolas]

with this stripped down circuit, I don’t see the point of a bigger mic body!

I like the compact size of the 102.

It is about headbasket micro-acoustics
It will not provide the correct lows and low-mids (and not only) of the U87

 

[elskardio]

It is about headbasket micro-acoustics
It will not provide the correct lows and low-mids (and not only) of the U87

I already have a pair of U87…
I’ll be more than happy if the result is something a little different!

 

[micolas]

I already have a pair of U87…
I’ll be more than happy if the result is something a little different!

If it's ok for you then it's fine

 

[elskardio]

Just double checking here... Only the 1G / Gate / FD connection needs to be floating. The back plate can be soldered directly to a PCB pad?

 

[Khron]

Just double checking here... Only the 1G / Gate / FD connection needs to be floating. The back plate can be soldered directly to a PCB pad?

If it's cardioid-only, yes, very much so. You shouldn't even need a very-high-value resistor between the last filter capacitor and that capsule terminal.

 

[Wordsushi]

Ok, I have a question.
So, I'm experimenting with a twin output 87, made with two identical boards, two identical Neutrik 10/3 transformers, wired into a 5 pin jack and using a no name dual sided generic k87 with a shared backplate.

When I power on both sides, one side is out of phase. When I flip the phase on that side, the other side goes out of phase from it.

I've previously made dual-output mics with other circuits and capsules, but I believe those capsules had separated backplates. (Update: I checked one of my other dual-output mics that has an M7 style capsule with one shared backplate and polarity lead and both sides are in phase)

When I plug in my Townsend Sphere mic, both sides are in phase, yet it also has a dual sided capsule with a shared backplate (797 CY-002). I can confirm there is only one backplate wire going to the capsule on the Sphere.

What I can tell you is that both boards were working properly in separate mic bodies, perfectly in phase. Levels on both seemed to match which is why I decided to try them in a stereo prototype. Double checked and transformer and XLR are wired correctly.

The 5 pin jack is wired the same as the Sphere mic.

pin 1 - Ground

pin 2 - Front XLR 2

pin 3 - Front XLR 3

pin 4 - Rear XLR 2

pin 5 - Rear XLR 3

So, what is the fix for this to make both sides in phase? What am I missing here?

 

[OneRoomStudio]

You need a capsule with isolated backplates to do that (four connections). The only other way to do it would be to supply one side with twice the voltage that you have on the backplate. In other words, you either need:
FD: 0v
FBP: 48v
RBP: 0v
RD: 48v
(with isolated backplates)
Or
FD: 0v
(shared) BP: 48v
RD: 96v

You could also put 48v on the rear diaphragm and 24v on the backplate, but you’d lose 6dB of sensitivity.

 

[Wordsushi]

You need a capsule with isolated backplates to do that (four connections). The only other way to do it would be to supply one side with twice the voltage that you have on the backplate. In other words, you either need:
FD: 0v
FBP: 48v
RBP: 0v
RD: 48v
(with isolated backplates)
Or
FD: 0v
(shared) BP: 48v
RD: 96v

You could also put 48v on the rear diaphragm and 24v on the backplate, but you’d lose 6dB of sensitivity.

Thank you (yet again!). You saved me hours hunched over this thing looking at everything under a magnifying glass. I'll just put a pin in it for now and pencil in a capsule with isolated backplates for my shopping list on this project.

 

[Wordsushi]

This morning, someone asked me about using a 6.5:1 transformer with this circuit and I honestly wasn't sure what it would do, so I told them it would most likely explode, killing everyone within a one-block radius, which I now think is incorrect. But I thought I'd post that question here so that someone much smarter than me can give an accurate answer, but I'm keeping my flak jacket on until then.

 

[micolas]

This morning, someone asked me about using a 6.5:1 transformer with this circuit and I honestly wasn't sure what it would do, so I told them it would most likely explode, killing everyone within a one-block radius, which I now think is incorrect. But I thought I'd post that question here so that someone much smarter than me can give an accurate answer, but I'm keeping my flak jacket on until then.

Nothing will explode
Only the output impedance of the microphone will be higher
(some mic preamps won't like it, but it will work)
The output level will be higher.
In the KM84 circuit, the transformer has a ratio of 6.5:1 - 7:1 and is a U87 without de-emphasis
I tested a transformer with a 2:1 ratio in the U87 circuit and no smoke came out, it just narrowed my frequency band, it sounded less bassy and as if even less treble, more Lo-Fi, but I liked it , character from the 70s.
I reduced the jFET drain resistor below 10k (!) the absorbed current was higher, but nothing exploded
So for testing, until get a suitable transformer can experiment with 6.5:1.
The de-emphasis will probably be different and possibly decrease the polarization voltage of the capsule a little

@Wordsushi you can do the experiment yourself: you only need to replace the red wire with the blue one on the Neutrik nte10/3 transformer and you will have a ratio of 7:1
I did this a few years ago in the U87ai circuit and it sounded even more saturated, more exciting, with more emphasized mids/high-mids.

A little DIY adventure is always exciting

 

[Wordsushi]

Thank you. I still told him it was going to explode and he cried and cried. But he is six years old and he'll just hide in the basement for a few hours, and then I'll cheer him up by telling him we're going over to a buddy of mine's house where he just installed the 6.5:1, and instead I'm going to drive up to this old burned out warehouse in the next town over and say, "Oh no! The transformer exploded!" It'll be great. Thanks again.

 

[Geariatric]

Thank you. I still told him it was going to explode and he cried and cried. But he is six years old and he'll just hide in the basement for a few hours, and then I'll cheer him up by telling him we're going over to a buddy of mine's house where he just installed the 6.5:1, and instead I'm going to drive up to this old burned out warehouse in the next town over and say, "Oh no! The transformer exploded!" It'll be great. Thanks again.

Man, this post sure brings back memories.

 

[Wordsushi]

Man, this post sure brings back memories.

Hahahahaha!!!

 

[Wordsushi]

I just wanted to report back two things:
I've been building Homero's board with the updated (Khron's) BOM and overall, I can't hear any difference between it and mics built with the original BOM. I haven't done any measurements if it's quieter or cleaner, but I can say for certain that it does not alter the tone or intent of the original circuit. And it's easier since there are fewer different parts. Just really confirms what has been said here before about this being a very forgiving circuit you can pretty much build without sticking to the same list of parts.

Second: I'm starting to like that $18 Ali T-13 transformer. I'm noticing the two I've built with these transformers sound the most alike to my u87, despite having different capsules and being in different sized bodies. I had written this one off initially, but now I'm re-evaluating.

 

[micolas]

I just wanted to report back two things:
I've been building Homero's board with the updated (Khron's) BOM and overall, I can't hear any difference between it and mics built with the original BOM. I haven't done any measurements if it's quieter or cleaner, but I can say for certain that it does not alter the tone or intent of the original circuit. And it's easier since there are fewer different parts. Just really confirms what has been said here before about this being a very forgiving circuit you can pretty much build without sticking to the same list of parts.

Second: I'm starting to like that $18 Ali T-13 transformer. I'm noticing the two I've built with these transformers sound the most alike to my u87, despite having different capsules and being in different sized bodies. I had written this one off initially, but now I'm re-evaluating.

Can you post a picture of the circuit?
What capsule did you use?
Arienne K87v1 or v2, CY-002, TSC-2 ?
I'm just about to place an order with Mouser and I don't know if I should order more 2N3819 or try the LSK189 as well. You didn't talk much about this jFET, even if it is more expensive, if it has lower noise and a good sound in this circuit it would be worth it. In the posted test you left the fan in the vocal booth on, which did not help me in evaluating the microphone's self-noise with the LSK189.

 

[micolas]

I'm starting to like that $18 Ali T-13 transformer. I'm noticing the two I've built with these transformers sound the most alike to my u87, despite having different capsules and being in different sized bodies. I had written this one off initially, but now I'm re-evaluating.

From an online store in my country, I bought several Neutrik nte10/3 for 9 euros, shipping included, a few years ago, I installed them in different microphones. I really like them, they have a special coloration. I just noticed that they have again in stock for 8 euros, cheaper than Mouser or Thomann and I can receive it in 2 days.
Your reviews of Ali T-13 are a bit confusing for me. I haven't tested it, but it has a bigger magnetic core (like Ami T-13) that means it saturates harder, I would try it with a bigger signal in the U87ai.
On the other hand, it is more expensive and I have to wait a long time to receive it. (An Ali order placed more than 2 months ago has not arrived even now)
So which do you like better:
Neutrik 10/3 or Ali T-13 ASTDS?
(I have repeatedly noticed that you have preferences regarding the sound, the character of the microphones very close to mine)

 

[Wordsushi]

There's a couple of photos of the Homero board build in the thread, one here:
https://groupdiy.com/threads/open-source-diy-mic-project-ors-87-stripped-down-u87.86814/post-1147018

I've my other builds up side by side with the one with the LSK-189 and I didn't hear enough of a difference from my NOS batch of 2n3819's I'm starting to run out of. I have one more 189 that I'm going to insert into yet another build before I really attempt to see if I can hear any difference, but practically, I didn't hear anything that made me think it will be a huge improvement at 4x the price of a new 2n3819. Is there more consistency between 189's than 3819's? I don't know yet. It's on my list of things to try and explore. I left the fan on in my test because I work with the fan on and it helps me better understand what my working environment noise levels are.

The capsules used in the mics with the Ali T-13 are a 797 audio one sided K87 from a Studio Projects C1, not sure what the product number is on that, and then also a generic capsule pulled from a cheap BaiFei Li mic. As I continue my tinkering, it'll be interesting to see what happens if I put better capsules on these.

Also to be noted, the two items I listed in my post are not necessarily related as the mics I had built with the Ali T-13 predates receiving the Homero boards so those two were built with the original BOM. Compared to my other mics built with the same BOM, seen here (https://groupdiy.com/threads/open-source-diy-mic-project-ors-87-stripped-down-u87.86814/post-1146886) these do sound more like a real 87 than the others I have built with the GZT-87t and the Neutrik. But as this is an evolving set of tests happening, this isn't my final conclusion, but rather me signaling that I was wrong to dismiss the Ali T-13 as an option I like.

As for which I like better? Still too early to tell. I like the Neutrik and had written the T-13 off, but my views on these are evolving. I changed the capsule on one with a T-13 to the 797 and it really just came together, so it's really more likely not whether one is better than the other, but dependent upon what goes with what, so it's a larger data set to evaluate than I had first thought when it comes to these transformers. Finding the right recipe.

 

[micolas]

The capsules used in the mics with the Ali T-13 are a 797 audio one sided K87 from a Studio Projects C1, not sure what the product number is on that

Is capsule 797 in Studio Projects C1 white or pink?
The white one appears to be the same one used in the Behringer B-1 old model with trough hole components
The pink one looks like the one used in Studio Projects B1 (but this one has a 3 micron diaphragm)

 

[Wordsushi]

Pink one from a gen 2 C1.