Neumann Vintage U87 Clone : Build Thread.

[andyfromdenver]

*sound of champagne bottles popping*
O.M.G.
I finished it and it sounds amaaaaaaazing!  I'm at a loss for words.
Heart felt thanks and pending buddy list requests to the posters who have helped:
Dany for the hard work designing the circuit/ compiling BOM and so many other details.
Matador for the (mostly over my head!) input on optimizing the microphone.
Chunger for the big pics.
Dave for clarification of the wiring.
Udo for the header clarification.
Evanmurphy for posting the t87 scheme.
Ralph who used the copper cap from the hardware store for an impromptu transformer housing.
And last but not least, John Peluso for the killer capsule and transformer.

Just too cool  8) 8) 8) 8) 8)

Sincerely,
Andy

 

[andyfromdenver]

PS.  Though I haven't put it through it's paces as it's late.
I used the 60M resistors.
The gain seems perfectly fine and great, I wouldn't say it's low gain at all if this has made some hesitant to take the plunge.
It's superbly quiet and seems to be grounded nicely.
The sound has a really nice (i'm horrible at describing these things) beef to it.  It's not bright/ harsh, and sounds like a very expensive microphone.  Crazy.....
Here's a pic of the copper cap. (for this body) I used a 1" copper cap, had to cut it down with the dremel and drill a hole in the top.  Used a rubber grommet for the hole and temporarily just electrical taped it to the rails/frame.  Also, I accidentally broke the little isolation pin for the source, so just ran the lead up through the hole and soldered direct and floating, no problem. 
The only things left to do are to screw the copper cap down and devise some switches.

 

[kante1603]

Congrats Andy and merry christmas!

Udo.

 

[atticmike]

Any chance someone might answer my questions during the holidays?

 

[tskguy]

Atticmike,

There is no need to change any capacitor values at all, simply build the circuit as is and like Dany said if you do not have a scope simply plug the microphone in to a phantom powered pre amp through the XLR connector. Then use your multimeter to measure the voltage at the drain of the fet. Use the potentiometer installed at r11 to adjust the voltage you see at the drain to be 11.5 volts. This will get you very close. In fact the last pair I built I set the drain voltage to be 11.5 and I scoped it and didn't need to change it at all. That's it! And just leave the potentiometer in place it's just fine. Don't change any capacitor values!!!!!! The ones Dany specked are perfect.
Eric

 

[3nity]

why dont use sockets on the 2n3819 legs??
as Poctop said you can dial a 11.5V drain and you pretty much are there...
that what i did.
Thank you.

 

[atticmike]

Thanks guys.

But for what is the "calibration cap" good for? I mean, it's included in the bom after all?

 

[kante1603]

Thanks guys.

But for what is the "calibration cap" good for? I mean, it's included in the bom after all?

Hi Mike,
the cap is just meant for temporarily use.It is there to complete the circuit instead of using the real capsule e.g. you must troubleshoot or measure something and don't want to be risky with it,it's the most expensive and sensitive part of the build.
The cap just simulates the capsule,remember a capsule is a capacitance,in this case it would be like some 50 pF or so if I remember correctly.
You don't need to build it in,it's for other purposes only.
You also mustn't attach anything to the capsule connection pads during biasing the unit,leave them open at this moment.
Put the signal generator to the junction of c4 & r6(it should be mounted reversed,at least it was on the old boards,easy to reach then) and measure at the fet's drain.You do the scope method?

Cheers,

Udo.

 

[atticmike]

Thanks guys.

But for what is the "calibration cap" good for? I mean, it's included in the bom after all?

Hi Mike,
the cap is just meant for temporarily use.It is there to complete the circuit instead of using the real capsule e.g. you must troubleshoot or measure something and don't want to be risky with it,it's the most expensive and sensitive part of the build.
The cap just simulates the capsule,remember a capsule is a capacitance,in this case it would be like some 50 pF or so if I remember correctly.
You don't need to build it in,it's for other purposes only.
You also mustn't attach anything to the capsule connection pads during biasing the unit,leave them open at this moment.
Put the signal generator to the junction of c4 & r6(it should be mounted reversed,at least it was on the old boards,easy to reach then) and measure at the fet's drain.You do the scope method?

Cheers,

Udo.

Alright, I was just wondering whether I needed the cap for calibration since the capsule has to be disconnected from the body.

 

[3nity]

in my mic i wired everything,
then plugged the mic to preamp, switched 48V and dialed 11.5V at drain....thats all i did and it works.
off couse i later switched from trimmer to resitor..

 

[poctop]

Big Thanks Trinity and Big Thanks To Andyfromdenver ,  nothing makes me happier than happy build people that is a real treat ,

Thanks
Sincerly
dan,

 

[atticmike]

Thanks guys.

But for what is the "calibration cap" good for? I mean, it's included in the bom after all?

Hi Mike,
the cap is just meant for temporarily use.It is there to complete the circuit instead of using the real capsule e.g. you must troubleshoot or measure something and don't want to be risky with it,it's the most expensive and sensitive part of the build.
The cap just simulates the capsule,remember a capsule is a capacitance,in this case it would be like some 50 pF or so if I remember correctly.
You don't need to build it in,it's for other purposes only.
You also mustn't attach anything to the capsule connection pads during biasing the unit,leave them open at this moment.
Put the signal generator to the junction of c4 & r6(it should be mounted reversed,at least it was on the old boards,easy to reach then) and measure at the fet's drain.You do the scope method?

Cheers,

Udo.

But I thought the capsule has to be disconnected during calibration as it's mentioned on the first page? So I rather think they're needed if the built's already done and you need to troubleshoot it?

in my mic i wired everything,
then plugged the mic to preamp, switched 48V and dialed 11.5V at drain....thats all i did and it works.
off couse i later switched from trimmer to resitor..

Alright, but you still left the capsule disconnected during calibration and connected it afterwards right?

 

[kante1603]

That's what I wrote.......

You also mustn't attach anything to the capsule connection pads during biasing the unit,leave them open at this moment.
Put the signal generator to the junction of c4 & r6(it should be mounted reversed,at least it was on the old boards,easy to reach then) and measure at the fet's drain.You do the scope method?

....and I asked if you do the scope method........

Udo.

 

[atticmike]

That's what I wrote.......

You also mustn't attach anything to the capsule connection pads during biasing the unit,leave them open at this moment.
Put the signal generator to the junction of c4 & r6(it should be mounted reversed,at least it was on the old boards,easy to reach then) and measure at the fet's drain.You do the scope method?

....and I asked if you do the scope method........

Udo.

scope method... but would it matter?

 

[HellfireStudios]

The scope method tends to get the optimal setting for headroom and overall gain.

-James-

 

[tskguy]

Atticmike,

Ok here is the deal, The scope question is an important one. Here is why, if you dont plan on using a scope to bias you can build the microphone completly transformer capsule and all!! You simply complete the mic and then use yur DMM to set the voltage at the drain. This can be done with everthing installed. Cool? If you use the scope its key to not have the capsule and transformer installed...Everything else is installed. The 50pf cap leave it off. Save it for another project! I have never used them. 

Good luck!!

 

[joeman7890]

I am almost finished with the circuit boards but I just need some help finishing them up and starting to bias the FET. I attached some hi-res pictures so it's easy to see.

My first question is whether the R11 pot is in the correct place. I have pin 1 on the left and haven't soldered it yet.

My next question is whether the middle FET leg is correct. I had installed it wrong at first but I was wondering if this is right.

When biasing the FET once I have everything connected except the Capsule. What do I set my DMM to look for? I want to just do the method that measure 11.5 at the drain. Can someone please write out how to do that or point to where it is documented?

Any help is greatly appreciated as I am so close and have loved the community help so far on this thread.

PICTURES:

http://blog.joeclarmusic.com/images/U87_End/R11_Pot
http://blog.joeclarmusic.com/images/U87_End/R11_Nothing
http://blog.joeclarmusic.com/images/U87_End/B2

 

[poctop]

I am almost finished with the circuit boards but I just need some help finishing them up and starting to bias the FET. I attached some hi-res pictures so it's easy to see.

My first question is whether the R11 pot is in the correct place. I have pin 1 on the left and haven't soldered it yet.

My next question is whether the middle FET leg is correct. I had installed it wrong at first but I was wondering if this is right.

When biasing the FET once I have everything connected except the Capsule. What do I set my DMM to look for? I want to just do the method that measure 11.5 at the drain. Can someone please write out how to do that or point to where it is documented?

Any help is greatly appreciated as I am so close and have loved the community help so far on this thread.

PICTURES:

http://blog.joeclarmusic.com/images/U87_End/R11_Pot
http://blog.joeclarmusic.com/images/U87_End/R11_Nothing
http://blog.joeclarmusic.com/images/U87_End/B2

From Here , you pot is properly installed and the FET transistor also ,  you need to connect the mike to a preamp with the phantom power on and then set your DMM to look for DC voltage then stick the red probe on the drain pin of the fet and the black probe to ground or mic rail  and then set 11.5VDC t this point ,
hope this helps,
Dan,

 

[wave]

Also,
If you do this method (no scope) you should have everything connected capsule and all (if you don't want to connect the capsule then you would use the (2) 50pf ceramics in place of the capsule. At least that's how I did it.

Dave

 

[andyfromdenver]

Hi guys!
  Had a chance to AB the mic at a friends studio.
did a few scenarios.  For vocal work we set it up as close as physically possible to a Pelusso 2247.
The mics were very very close in sound.  Eerily close and could have been a useable overdub substitutes in a pinch.  I felt like a proud father with my self made mic; we were both stunned with the nice results.
  One observation was that the polarities were opposite.
Do I need to go in and flip either the primary or secondary sides?  Or leave it?
  Also, a purely cosmetic concern, I wired in switches, but am tempted to take em out and put the molex headers back in.  It's no biggie to open the mic to make connections, and I was unable to show the guts off to friends!  If I do this, I'll have to make some fancy badge to cover the holes.