Neumann Vintage U87 Clone : Build Thread.

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But it should have been in phase if you wired the transformer in either way, so I'm still confused. Maybe the other mics are out of phase?
I was comparing with stock SM57s so I believe the wiring simply inverted the polarity since out of phase is relative
 
Just want to double check my ill/ tired brain has these right:

Used a wheatstone bridge this evening to match up the 2.2k resistors that need to be within 0.4%. Am I reading the schematic right that they're the ground reference/ virtual centre tap for the secondary side of the transformer? Presumably it's easier to get an accurate centre tap this way than by putting a centre tap inside the secondary itself coming out with a 5th wire from the transformer?

Main question:

So... four 2.2k 1% resistors go in the Wheatstone bridge "diamond". I had 20, so that means 17 to substitute. I record the mV difference across the two parallel pairs as I go. The two that give the closest value difference to each other are best matched.

The thing I don't understand is, the instructions I've found then say to make those matched resistors side A, and start subbing two different resistors into side B to find the value closest to 0mV, and then THOSE, on side B, are the match. But haven't you already found the match to populate side A? Why bother with the last step if you only need to find 2 matched resistors for the circuit? By the end of the instructions you've got two matched pairs - side A and side B, even if they differ from each other?

As it stands, I'm making two mics so I did want to find two pairs;

I put 4 random resistors in, measured the mV difference, cycled the other 16 resistors through that position recording the mV difference for each, popped the results into a spreadsheet to find the two nearest values (7.31 & 7.53 mV), those two resistors became my first matched pair, used the spreadsheet to find the *next* two nearest values (1.57 & 1.8mV), and those became the second pair. Double checked by putting the two matched pairs into the Wheatstone bridge, and the Multimeter read 0.00mV. So... Am I done? Have I made a terrible mistake? 🤣 I did a sanity check of just measuring the resistance of my pairs & got 2.204k for the first pair, and 2.199k for the second, so it seems like they're matched closer than 0.4%...
 
Hello! New member here. Hope I'm posting in the right place for troubleshooting...

I inherited a partially built U87 clone kit. Its the green taper board by Dany. The PCBs were already populated, so I just had to connect the 3 boards via jumper wires, and connect the transformer and XLR jack. Capsule is not installed yet. I'm having trouble calibrating the FET in order to determine the value of R11. I am not seeing a voltage anywhere near the 11v/12v target range. Spent last couple days reading threads on this forum but still stumped. Confirmed that all values/ orientation of components are correct. Hopefully someone can point me in the right direction. Here is what I have so far:

-R18 and R19 are matched
-Transformer is the CM 13113. With the following wire connections to the PCB: RT pad 1 to red wire/ SW pad 2 to brown wire/ BL pad 3 to orange wire/ WS pad 4 to yellow wire.
-The FET was already installed in the PCB. I am told the FET was purchased as part of the "kit" but I do not know the IDSS measurement. The gate (center pin) is connected to a floating pin labelled GG.
-Pads A, B, C and G on board 2 are all connected to their respective pads AA, BB, CC and GG on board 1.
-R6 is installed opposite the silk screen

When I place my DMM positive (red) probe on R6 and negative (black) probe on ground, the voltage I read is basically 0v regardless of the resistance value on the multiturn trim pot which I have temporarily patched into R11. The trim pot has one ear connected to the Drain pin of the FET, and the trimmer wiper is connected to ground. Why am I not seeing a voltage here anywhere near the 11v/12v target range?
A few additional questions:
-what is the pad labeled "GNDLINK" for? Should this be connected to something?
-should the two larger pads/holes labeled SW and RT be connected to something?

Thank you for any direction!
 

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Hello! New member here. Hope I'm posting in the right place for troubleshooting...

I inherited a partially built U87 clone kit. Its the green taper board by Dany. The PCBs were already populated, so I just had to connect the 3 boards via jumper wires, and connect the transformer and XLR jack. Capsule is not installed yet. I'm having trouble calibrating the FET in order to determine the value of R11. I am not seeing a voltage anywhere near the 11v/12v target range. Spent last couple days reading threads on this forum but still stumped. Confirmed that all values/ orientation of components are correct. Hopefully someone can point me in the right direction. Here is what I have so far:

-R18 and R19 are matched
-Transformer is the CM 13113. With the following wire connections to the PCB: RT pad 1 to red wire/ SW pad 2 to brown wire/ BL pad 3 to orange wire/ WS pad 4 to yellow wire.
-The FET was already installed in the PCB. I am told the FET was purchased as part of the "kit" but I do not know the IDSS measurement. The gate (center pin) is connected to a floating pin labelled GG.
-Pads A, B, C and G on board 2 are all connected to their respective pads AA, BB, CC and GG on board 1.
-R6 is installed opposite the silk screen

When I place my DMM positive (red) probe on R6 and negative (black) probe on ground, the voltage I read is basically 0v regardless of the resistance value on the multiturn trim pot which I have temporarily patched into R11. The trim pot has one ear connected to the Drain pin of the FET, and the trimmer wiper is connected to ground. Why am I not seeing a voltage here anywhere near the 11v/12v target range?
A few additional questions:
-what is the pad labeled "GNDLINK" for? Should this be connected to something?
-should the two larger pads/holes labeled SW and RT be connected to something?

Thank you for any direction!
So i made some progress troubleshooting and I have now adjusted the drain voltage on the FET to 11.3V. I had my xlr wires wired incorrectly (duh!).

However, there is some conflicting information as to the correct wiring for the CM-13113 transformer. I think what I listed above is incorrect according to the transformer datasheet. The mic schematic appears to show the secondary side (BL and WS) is connected to the XLR side and the primary side (RT and SW) connected to the capsule side of the circuit. That would make the CM-13113 connections as follows:
RT=brown
SW=red
BL=yellow
WS=orange
Can anyone verify my thinking is correct? And does the primary or secondary orientation even matter?
Thanks.
 
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Finally I’ve got mine. Used jfet with 8.17ma Idss. And after calibration drain voltage was about 7v. It’s quite lower than other diyers work but it sounds great to me.

I suffered from weird working figure 8(low output, works like cardioid) last night, so I swapped capsules from Arianne audio to 3u. But backplates of 3u were not isolated(or maybe I messed up that poor thing.) So cleaned the PCB and got back to Arianne one, now it’s fully functional microphone.

I still don’t know what was my problem… haha. Feel so good anyway. Thank you dan and solioqueen for providing great sources of diy.
 
It's definitely interesting working with such high impedances - I've only worked with guitar amps and pedals before, so dealing with a 1G resistor where just leaving sweaty fingerprints on it could conceivably be a more attractive path for current is new to me.

I'm building two, one of my capsules has no continuity between backplates but the other is around 5 meg, so might need changing if Fig8 doesn't work right. 5M seems so high that probably giving it a stern look would add a few more meg on... I wonder if just removing and returning the capsule might have been enough to physically move the backplates relative to each other and restore their isolation?
 
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Finally I’ve got mine. Used jfet with 8.17ma Idss. And after calibration drain voltage was about 7v. It’s quite lower than other diyers work but it sounds great to me.
I initially biased mine to whatever that number was that has been posted here, but one day I decided to get motivated and do a scope biasing, and mine both biased up at about 8.5 volts.

My 3819s are vintage Fairchild, and the Idss was mid 5's for both IIRC.

Also, there should be a post somewhere in this thread where someone said Neumann's number was different than the number posted here. Don't remember much more than that.

I do want to build 2 more of these with Moby's trafos.
 
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Mine pair are 3.6 & 4.8ma, I think they're old Texas Instruments ones but don't know enough to be sure - they came from a big parts box that someone I know found in a car boot sale. I should be in a position to bias them later this week, will report back with where they land.
 
Right, my pair ended up with a bias voltage of 9.3 & 10.45v. I'm sorry to say I lost track of which IDSS fet was which, but looking at the numbers on this page I'm kind of guessing that the 10.45v one is the 3.6ma and the 9.3v is the 4.8ma one.

Very gratifying process, doing test tone biasing. It's really nice to be able to dial in the last bit by ear - was way easier to hear the 2nd harmonic creep in audibly vs looking at the scope.
 
I ordered some 2N3819s from ebay. It has marking '2N3819 TIP512' and was painted like TI ones on another side. I don't know it's a real one, but it works. I used one that has 3.59mA IDSS and when calibration ended with a scope, drain voltage was 9.7v. I think I should stop now because I'm satisfied with the result and Jfet pad is almost ripped🥲
 
In a distant past, there were transistor sockets. I don't know if they still exist, though.
EDIT: Mill-Max still makes them, they are available from Mouser.
I have a socket strip. But I know I won’t stop till those get loose…
 
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Can you use the Studio Projects C1 body as a donor body for this u87 build? I have 2 sitting around... If so, which version of the PCB's do I need? Thanks!

Matt
 
Hey guys, does anybody use Moby's Bv.13 in the D-87M blue?
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Maybe someone can help me with wiring.

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This is from Moby's Site.

is it correct that i have to solder the 2 white one in the PRI together and in the SEC green and yellow?

Then connect it to the PCB:

black --> P+
red --> P-
white --> S+
blue --> S-

is that correct?
@Moby ? :cool:
Thanks in Advance!

Damian
 
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