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

[OneRoomStudio]

Thank you so much for sharing this layout. are the components between the capsule and R7 housed in the head basket on a different board ?

No, in this case, there are no other components. The capsule wires directly to the two points, FD (front diaphragm) and BP (back plate). This circuit is based on a simplified version of the U87, with no PAD, HPF, or pattern-selection switches, and is cardioid-only, which is why R1-R6 and C1-C4 are not present (they're used in the original circuit for the PAD, HPF, and pattern-selection).

 

[ubxf]

Got it thank you so much

 

[Jarbcd]

2. The fake TLM103 has a headbasket with U87 dimensions. The capsule needs to be raised higher and ideally a dome or some foam (like Basotect) added below to deflect/dampen reflections from the metal bottom.

How far would you raise the capsule?

 

[micolas]

How far would you raise the capsule?

I liked it the most (a sound closer to the U87ai, with less highs and more mid-highs) when the edges of the capsule were about equal distances from the sides and the top of the interior headbasket.

 

[living sounds]

I liked it the most (a sound closer to the U87ai, with less highs and more mid-highs) when the edges of the capsule were about equal distances from the sides and the top of the interior headbasket.

Looks good, I raised the capsule to the same hight as in the U87.

 

[Jarbcd]

I liked it the most (a sound closer to the U87ai, with less highs and more mid-highs) when the edges of the capsule were about equal distances from the sides and the top of the interior headbasket.

Is that a dome I see to counter the flat metal base?

Looks good, I raised the capsule to the same hight as in the U87.

I'm not familiar with the physical specs of the u87, do you have a read on how high the capsule bottom is off the base-plate?

 

[living sounds]

I'm not familiar with the physical specs of the u87, do you have a read on how high the capsule bottom is off the base-plate?

No, but pictures online should get you in the ballpark. The important thing is to get some distance between the capsule and the reflecting base.

 

[Wordsushi]

I'll do you one better. Here's the layout:
View attachment 124217
"X1/P-" at the bottom means "XLR Pin 1 and transformer Primary -." You can figure out the rest. The blue line is just used to show that it doesn't intersect the gray lines it crosses. All touching gray lines do connect.

Here's the BOM. Part names somewhat match the original U87 schematic for reference. Tweak to taste:
R7: 1G
R8: 1M
R9: 7k3
R10: 25K Trimmer
R12: 47k
R13: 330k
R14: 10k
R15: 300k
R16: 56k (for 24V zener, try 47k for 33V zener)
R18 & R19: 2k2 (closely matched!)

C5: 33n (can go as big as 330n if you want more low-end)
C6: 220p (treble cap - smaller = more treble, bigger = darker)
C7: 1u (can tweak to taste. smaller = less bass)
C8: 20u 6v
C9: 470n
C10: 4u7 35V
C11: 4u7 63V
C12: 10u 63V
C13: 10n

Q1: 2N3819

GR1: 1N4749A (24V zener - can try 33V instead with smaller R16)

Tie the XLR Pin 1 to the ground tab on the XLR connector. Film caps should be at least 63V. Use teflon-insulated pins for the capsule connections and keep those junctions "in the air." The board needs to be about 38mmx80mm. Careful not to short to the rails (I used electrical tape to insulate behind the board). Any K67/K87 type capsule should work. Any 8:1 through 12:1 OT should work.

Experiment!

By any chance do you also have a schematic? I'm trying to troubleshoot one I had to layout differently to fit a smaller body.

 

[OneRoomStudio]

By any chance do you also have a schematic? I'm trying to troubleshoot one I had to layout differently to fit a smaller body.

It’s exactly the same as the U87i schematic, including the same part designators - I just removed the parts that aren’t needed. I can draw it out tomorrow though, if that’s helpful.

 

[Wordsushi]

It’s exactly the same as the U87i schematic, including the same part designators - I just removed the parts that aren’t needed. I can draw it out tomorrow though, if that’s helpful.

That is very generous of you to offer. Let me take another look at the 87i schematic and try to suss it out and if I still can't make heads or tails of it, I'll throw up a flare.

 

[OneRoomStudio]

Here you go. Just a simplified U87i.



One note - I just simulated it, and due to the lack of the rear capsule components (including C1/C3), C6 has a little more pronounced of an effect on the top end. Changing it to around 120pF instead of the stock 220pF seems to match the original curve fairly well. Feel free to experiment.

 

[Wordsushi]

Here you go. Just a simplified U87i.

View attachment 124983

One note - I just simulated it, and due to the lack of the rear capsule components (including C1/C3), C6 has a little more pronounced of an effect on the top end. Changing it to around 120pF instead of the stock 220pF seems to match the original curve fairly well. Feel free to experiment.

Oh wow! I can't thank you enough. This is really great of you.

 

[Jarbcd]

For some reason they use a 470p cap in parallel with the 1M resistor for the high frequency correction. Replacing that cap with a 220p cap (as in the U87i) corrected the problem. The polystyrene looking cap in the middle of the PCB has nothing to do with the audio circuit, it's a 470p PSU bypassing cap. Best to replace that with COG ceramic.

I went pretty deep into it a couple years ago until I had the response very close to my Andreas Grosser modded U87ai:

1. Replace the tiny trafo with a UTM0587.

2. The fake TLM103 has a headbasket with U87 dimensions. The capsule needs to be raised higher and ideally a dome or some foam (like Basotect) added below to deflect/dampen reflections from the metal bottom.

3.1. Remove the two 2.2k resistors, replace them with through hole components of the same value mounted upright and summed together. From there take a 56k resistor (I used 47k, which is fine, you need to isolate the stage otherwise there can be oscillation on the outputs) to cathode of a 24V zener, which should be in parallel with the cap filtering the drain voltage. I added an additional filtering stage with a 10k resistor + ca 5uf cap, this is all per the v16 U87 schematic (you can find it online). From there it goes through a 100k resistor, which also needs to be taken out and replaced with 47k (I used through-hole again). Now you have a clean voltage feeding the drain side of the FET.

3.2. Remove the source resistor and replace it with a 10k variable resistor (trimpot). Set the bias per the instructions (availible online) via the Messeingang (6.8k and 560 ohm resistor were flipped on all of my mics, so exchange them).

I've attached a photo of the fully modded PCB with the parts named as in the old Neumann schematic also attached.

3.3. A simple pad (as in the U87) can be achieved by adding a cap in parallel with the capsule. Neumann used 560pf.


Much of the secret lies in being very diligent with the fet bias setting. I used a 256B transistor, like Andreas Grosser.

Ultimately this mic sounds very close to the real thing, but lacking some of the detail sonic sophistication. This would be down to the capsule (which is much better on that mic already than the average cheap chinese mic) and maybe the mesh structure, which is a little different on the Neumann mic.

Do you have any pics of the trafo swap that you did? I've got a UTM87 here and I'd love to do the same, but I think I'd need some guidance before I went on that adventure (tips are welcome!)

 

[living sounds]

Do you have any pics of the trafo swap that you did? I've got a UTM87 here and I'd love to do the same, but I think I'd need some guidance before I went on that adventure (tips are welcome!)

No, but measure the DC resistance of the transformer that is in there to determine primary and secondary, and then solder in the UTM trafo accordingly. You can download a spec sheet from their website.

 

[Wordsushi]

Here you go. Just a simplified U87i.

View attachment 124983

One note - I just simulated it, and due to the lack of the rear capsule components (including C1/C3), C6 has a little more pronounced of an effect on the top end. Changing it to around 120pF instead of the stock 220pF seems to match the original curve fairly well. Feel free to experiment.

SUCCESS!!
I just wanted to thank you again, profusely.
Got it working and I love it. I've tried a few times before over the years, just trying to build out a circuit on a prototype board and it's never worked. Not once. LOL. So this is a huge deal for me personally in my DIY journey.

Swapped out a 22uf 25v cap for the 20uf, because I had only bought 2 of the 20uf's and used them on a couple of builds that didn't work out. It's hard to find, so I may stick with the 22uf.
C6 is a 220nf and C5 is 150pf and I'm looking forward to building a few more of these and trying out some different components. This project is so cool. Thank you again. This is much better than my original idea of buying an Ali TLM193 to goof around with.

 

[OneRoomStudio]

Nice work! It’s a pretty fun circuit to play with. Glad my notes and diagrams were helpful. Prototyping a mic like this can be very empowering and open up more opportunities for experimenting with components. True DIY

 

[Khron]

Swapped out a 22uf 25v cap for the 20uf

Does anybody even make 20uF's anymore? Not that they're not (at the very least) +/-20% tolerance to begin with, anyway...

Not trying to be snarky, but how else will anyone take notice and consider trying to cure themselves of "vintage blindness"?..

 

[OneRoomStudio]

Does anybody even make 20uF's anymore? Not that they're not (at the very least) +/-20% tolerance to begin with, anyway...

Not trying to be snarky, but how else will anyone take notice and consider trying to cure themselves of "vintage blindness"?..

Not only that, but technically speaking, once you increase c6 all the way to 220nF, the cathode bypass cap actually becomes the limiting factor for the low end. The slight increase from 20uF to 22uF actually just allows a little more to pass below 60Hz (not a huge difference though)!

In all seriousness though, I wrote 20uF out of habit and to copy the original schematic, but 22uF is 100% fine there. That what I use.

 

[RuudNL]

Talking about Neumann and 'Ali' (Express): today I received this message.
It seems they now really have a problem with Neumann!

Dear Customer,

We hope this message finds you well.

Your satisfaction is of the utmost importance to us, and we strive to ensure that the products available on our platform meet corresponding standards.

We have identified a potential non-compliance issue with a recent product you have purchased.
Product Name:"U87AI studio microphone U87AI U67 M149 TLM103 TLM107 professional condenser mic pc gaming recording micro, u87ai with logo"
Cause for the potential problem: Intellectual Property Infringements
We take your safety and satisfaction very seriously, and we want to bring this matter to your attention promptly to ensure your shopping experience with us is in compliance with applicable laws and your expectations.

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If however there is actually no issue with the product, please disregard this message. If you have any concerns about the product or have any further related questions, you shall contact the seller directly. We regret any inconvenience this may cause.

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Best regards,
AliExpress

 

[Barry Hufker]

I'm surprised they have been able to skirt intellectual property laws for this long.