Can someone help me identify the attached U87 schematics?

[grobaesthet]

Hello to all!
4 years ago - just before my son was born, which radically stopped all my DIY-projects - I was working on a U87 RevA microphone using my studio projects C1 donor body with the C1 caspule. (The U87 Rev A is my memory of this project, perhabs I am also wrong with that?)
All bookmarks and files to this project got lost last year and all I have now is a copy of the schematic and two halfway soldered PCBs that don't seem to work as they should.
Either I start completely fresh with a new design or someone of you remembers the attached schematic and can point me to the built and its thread or informations to it.
I am very thankful for any help!
Best
Simon

 

[Khron]

Some of that schematic, especially in the capsule area, doesn't look quite right.

http://cdn.recordinghacks.com/images//mic_extras/neumann/U87-schematic.png
There's the 470pF DC-blocking capacitor missing (C4 in the original), between "PAD2" and R7 / JFET gate.

SW2 is connected in a very weird way; or rather the 1G R6 should be connected between the other side of SW2 and ground.

R11 should ideally be a trimpot, and adjusted in place for the exact JFET you're using (because their parameters can vary quite a lot - wide/loose tolerances).

[Later edit]
The circuit likely doesn't work (also) because the JFET gate is pulled to possibly as high as the 40-something volts of the capsule bias voltage, so there's also a (good?) chance that got fried.

 

[kingkorg]

The circuit likely doesn't work (also) because the JFET gate is pulled to possibly as high as the 40-something volts of the capsule bias voltage, so there's also a (good?) chance that got fried.

Hm, sure? Seems the gate is isolated from the pol.vol by the capsule. No dc path to the gate besides 1g resistor to ground.

 

[Khron]

Hm, sure? Seems the gate is isolated from the pol.vol by the capsule. No dc path to the gate besides 1g resistor to ground.

It was 8am on a friday...

 

[grobaesthet]

Hello Khron, hello Kingkorg,
thank you for your input!
I am pretty sure that I found that schematic here in GroupDIY, when searching for an easy U87 schematic for my existing SP C1 and its 34mm k67 capsule.
I wondered that it did not have the typical DC-DC-converter but thought it just might be a clever stripped-down-circuit.
But after your post Khron, I think I better search for another circuit to spend my little free time with and get the parts out of the non-working PCB.
Do you have (or anyone else reading this) have an idea of a U87-like FET-mic with just cardoid pattern and no switches? I neither need a pad or a filter on the mic, just want to have it as simple as it can get. But of course good sounding!
Thank you all and best regards!
Simon

 

[doqmemory]

Do you have (or anyone else reading this) have an idea of a U87-like FET-mic with just cardoid pattern and no switches? I neither need a pad or a filter on the mic

Perhaps the Dachman Audio DA87AE? It includes @soliloqueen 's excellent capsule. (I guess not, as the next post shows)

 

[soliloqueen]

Perhaps the Dachman Audio DA87AE? It includes @soliloqueen 's excellent capsule.

The SE doesn't include my capsule. I consulted on it, but it's more related to the Warm AYM capsules. Good capsule tho

 

[grobaesthet]

Thank you doqmemory and soliloqueen!

I was not aware of Dachman Audio and the reviews in TapeOp sound promising.

But my hope was to get pointed to a schematic (and building instruction) to build the mic on my own.
I have all the parts here (body, capsule, transformer and stuff) and would be happy to build the mic myself. My only problem is - as most of you probably saw within my first post - I am not really understanding the rules of microphone-electronics and am only able to rebuild a given schematic, as long as it is not too complicated.

Thanks and all the best!
Simon

 

[doqmemory]

Thank you doqmemory and soliloqueen!

I was not aware of Dachman Audio and the reviews in TapeOp sound promising.

But my hope was to get pointed to a schematic (and building instruction) to build the mic on my own.
I have all the parts here (body, capsule, transformer and stuff) and would be happy to build the mic myself. My only problem is - as most of you probably saw within my first post - I am not really understanding the rules of microphone-electronics and am only able to rebuild a given schematic, as long as it is not too complicated.

Thanks and all the best!
Simon

I don't think Josh (Dachman Audio) sells kits any more.

If you want a full kit, the MicParts S-87 or T-67 seem to fit your criteria. If you just want to "upgrade" your C1, they sell a U87 conversion kit for the C1. MicParts always has good build documentation included.

Your desire to use your C1 for this purpose is going to place some large constraints on this project.

 

[grobaesthet]

Thank you for the fast reply!

I already did the U87 conversion from microphone-parts on one of my C1s.
I have 5 studio projects C1 and did different modifications on them. But for this next project I would really like to do something from scratch, just using the K67 capsule and the body of the C1. Or the body of a Behringer B1 which lies in my drawer. I also already have the transformer and dozens of NOS caps and resistors that should work.
So a schematic of a stripped down U87 with just a cardoid capsule would be perfect for my need.

Thanks!

 

[Drosselmeier]

https://groupdiy.com/threads/ta27-simplified-u87-with-rk12-or-rk47and-nte10-3.63896/

 

[grobaesthet]

Thank you Drosselmeier!
These two circuits look very interesting and seem to be exactly what I was searching for!
My first impression: I think I will go for the U87 FET Frontend.
Thank you and all the best!
Simon

 

[grobaesthet]

Hi to all the smart people in this thread that helped me!

I now started another microphone project that waited in my drawer for the last two or three years...
It seemed to be exactly what I wanted: simple and straightforward.
But also with this circuit I ran into difficulties! Maybe you can also help me here?
I opened an extra-thread for this:
https://groupdiy.com/threads/phaedrus-audio-spirit-tube-u47-circuit-need-help-please.83938/
Thanks in advance and all the best!
Simon