Neumann Vintage U87 Clone : Build Thread.

[HosaMogami]

Hi all,

I seem to have a problem with the polar patterns on my u87 build, particularly the figure 8 pattern. When I measure voltage at the front and rear backplate, I get around 40V when set to cardioid or omni and measure around 6V when set to figure 8. I double checked all the wires from the switch pcb and seems to check out. Has anyone else had this problem? Cardioid sounds fine, Omni sounds like it's not fully utilizing the rear diaphragm and figure 8 just gives a very low signal, also not really utilizing the rear diaphragm.

Thanks in advance for any help!

I have this same issue... getting around 7v on the each backplate when in figure 8. Everything else works well. Any idea's?

 

[Ricardus]

I have this same issue... getting around 7v on the each backplate when in figure 8. Everything else works well. Any idea's?

Looks like I'm getting the same thing. I built 2 of these and one worked perfectly out of the box, and the 2nd one seems to be having this issue also. Omni and cardioid seem to be fine. Figure 8 is quiet on the front capsule and very quiet on the rear capsule.

Has anyone solved this issue?

 

[Ricardus]

I am a recording guy and an enthusiastic builder, but I am not a good diagnostic tech. I have a friend who is, and he gave me a few things to check, and to my eye everything on the mic with the figure 8 problem seems to be fine. This is super frustrating. The first mic worked right out of the box, the 2nd mic, which  I actually assembled 2nd, after the learning curve of the first one was behind me, and with as much patience and care as the first one, I would not have expected to be the one with issues. Oy.

 

[wave]

Hello everyone,

I am new here and just started building a u87 kit. 

I have a few questions and if you guys could help, that would be awesome! 

1.  The BOM part numbers 538-22-28-4030 qty of 2 connector vertical 3 position // 538-22-28-4020 connector vertical 2 position qty of  4 // 151-8010-E Mini Jumper GF 6mm qty of 3;  According to the information I have been able to find in this thread, I can see diyer's have made use of them on the PAD, OMN CRD and LC sections of the pcb.  That equates to two 2 positions and one 3 position connectors.  Where are the rest being used??  Also, why do we need the mini jumpers (151-8010-E)??  I don't see the use or need for them?  Can someone please enlighten me here? loll

2.  The second question I have is regarding "R11CAL" on pcb version 1.2 green tapered.  There are two parts on the BOM...mouser p/n 72-T93YA-25K trimmer and 81-PV37X253C01B00 trimmer.  I believe 81-PV37X253C01B00 trimmer is just meant as an option cause it's smaller?  I intend to use  the 72-T93YA-25K trimmer.  Can you guys confirm this?  So the next question regarding the trimmer is on the R11 pad section where am I inserting this part?  As I understand it, on this particular board, I should insert the trimmer's three pins right in the middle so that I can see the two holes on either end of the trimmer?  Also, from what I can see, the pcb is only using two pins on the pcb trace, correct?  Can someone just verify which of the holes from the trace lines in R11 are actually doing something with the trimmer.

3.  By now, its clear that the Fairchild 2N3819 is obsolete...loll.  So it seems like the NTE-312 is the replacement.  Has anyone experienced any problems when using this transistor?

4.  Also, can anyone recommend a particular style or brand of hookup wire?  I am trying to use the highest quality components on this mic and want to minimize the noise where ever possible. 

5.  When receiving my capsule, how would one go about checking the capsule for tuning?

6.  I noticed guys testing their mic's and generating these really cool graphs!  Where do I get my hands on that software so I can perform these tests as well?

Happy New Year everyone!

Welcome!
Here are some answers for you:
1. You don't need to use the jumpers/headers if you have the pad/pattern/lo-cut switches and just wire to the pcb. I think the other headers are for the transformer and XLR positions?
2. Yes the 72-T93YA-25K is the choice here. The other part has the screw on the side and the pins are staggered.
      I tried to upload a narked up pic of the trimmer  but the site gave me an error. The trimmer goes into the 3 middle holes, of the 5 holes associated with the R11CAL position
3. You should be ok with the NTE-312 but NTE has a 2N3819 as well...
      https://www.ntepartsdirect.com/ENG/PRODUCT/2N3819
4. Wire choice may be a bit subjective. I like this stuff as it's cheap and the jacket can take some iron heat..
      https://www.amazon.com/dp/B01KQ2LHFI/ref=twister_B07CPWCGML?_encoding=UTF8&psc=1
5. You can measure the capacitance of the capsule with a capacitance or LCR meter that can measure in picofarads. As far as the diaphragm tuning, you won't be able to.
6. Some people use R.E.W. (Room EQ Wizard) to do sweeps. You can also use some of the software that comes with measurement mics.

Hope these help!
Dave

 

[wave]

I have this same issue... getting around 7v on the each backplate when in figure 8. Everything else works well. Any idea's?

What kind of meter are you using to measure the polarization voltage? A normal DMM will load down the circuit there.

-Dave

 

[newmod]

Thanks so much Dave!

I really appreciate this as it does help!

Welcome!
Here are some answers for you:
1. You don't need to use the jumpers/headers if you have the pad/pattern/lo-cut switches and just wire to the pcb. I think the other headers are for the transformer and XLR positions?
2. Yes the 72-T93YA-25K is the choice here. The other part has the screw on the side and the pins are staggered.
      I tried to upload a narked up pic of the trimmer  but the site gave me an error. The trimmer goes into the 3 middle holes, of the 5 holes associated with the R11CAL position
3. You should be ok with the NTE-312 but NTE has a 2N3819 as well...
      https://www.ntepartsdirect.com/ENG/PRODUCT/2N3819
4. Wire choice may be a bit subjective. I like this stuff as it's cheap and the jacket can take some iron heat..
      https://www.amazon.com/dp/B01KQ2LHFI/ref=twister_B07CPWCGML?_encoding=UTF8&psc=1
5. You can measure the capacitance of the capsule with a capacitance or LCR meter that can measure in picofarads. As far as the diaphragm tuning, you won't be able to.
6. Some people use R.E.W. (Room EQ Wizard) to do sweeps. You can also use some of the software that comes with measurement mics.

Hope these help!
Dave

 

[Parabola]

Please help. I am having an issue calibrating the FET. I can hear my mic through Logic Pro and it sounds okay but at an extremely low volume.  I have to turn my pre all the up to max gain to hear it at a low-moderate level.

When I am measuring the voltage on the FET it reads 1.7 and I cannot make it go higher than that no matter how much I turn the trim at R11. I have my multimeter at R11-CAL and CGND.  Arn't I measuring the correct points on the PCB?


Any insight into what went wrong? Could my transformer wiring be flipped?

Thanks!

 

[TillM]

Sounds like a bad trimpot to me, when you can’t turn it up higher.
Had the same issue with one of my builds some years ago.
Can’t get a higher voltage on the drain then 5,6v. After changing the Trimpot everything worked well.

 

[wave]

Please help. I am having an issue calibrating the FET. I can hear my mic through Logic Pro and it sounds okay but at an extremely low volume.  I have to turn my pre all the up to max gain to hear it at a low-moderate level.

When I am measuring the voltage on the FET it reads 1.7 and I cannot make it go higher than that no matter how much I turn the trim at R11. I have my multimeter at R11-CAL and CGND.  Arn't I measuring the correct points on the PCB?


Any insight into what went wrong? Could my transformer wiring be flipped?

Thanks!

You need to measure the drain of the FET.  R11CAL is connected to the source pin of the FET.

-Dave

 

[Ricardus]

I have to say, the working D87 sounds amazing. Definitely the quality of a high-end condenser. We have an similar vintage U87 at the analog studio where I work and I plan to make some A/B recordings, but I just found out it doesn't work at the moment. So we need to get the actual Neumann working so I can compare.

Still no joy with my figure 8 issue on the other mic. I have a friend who is an excellent mic tech but he lives out of town, and he gave me some things to check, but no joy at the moment.

 

[HosaMogami]

What kind of meter are you using to measure the polarization voltage? A normal DMM will load down the circuit there.

-Dave

Thanks Dave,

  I am using a Fluke 73 III.  Seems strange, Ive got 4 of them that all show me only 7v when in figure 8 mode at this point. Its a bummer. I didn't cut one of the legs off of the set bias trim pots on these (because Ive done it that way before and had the build fully working) I never found clarification in this thread as to why one would need to do that. Not sure if that can contribute to my problem? But as I said Ive had success installing all 3 legs on previous D87 builds. Just spitballing the few ideas I have left at this point... Wish someone could help me wrap my head around this.

 

[Ricardus]

Is there any chance the figure 8 problem a few people are experiencing is from a bad capsule?

If I unhook the capsule from the circuit boards is it safe to test continuity between the backplates to make sure they're not shorted in any way?

 

[PG_Sax]

Is there any chance the figure 8 problem a few people are experiencing is from a bad capsule?

If I unhook the capsule from the circuit boards is it safe to test continuity between the backplates to make sure they're not shorted in any way?

You could try swapping the capsule / wiring - so the current front becomes the back and the back becomes the front. If you suspect the rear diaphragm is not working.

I'm guessing you have already checked the switch wiring and been over the circuit?

 

[Ricardus]

You could try swapping the capsule / wiring - so the current front becomes the back and the back becomes the front. If you suspect the rear diaphragm is not working.

I'm guessing you have already checked the switch wiring and been over the circuit?

I've been over everything as best I can. Swapping the front/rear is a great idea. I'll do that tomorrow....

I have a friend who is a great tech. He's a former radio station maintenance engineer, so this will be on his bench next week if I can't figure it out.

I just think it's interesting that two other people are having the same problem as me right now. 

 

[Ricardus]

I might have found the issue with figure 8 mode in my mic. Looks like I have continuity between the backplates, and I'm pretty sure there isn't supposed to be any on the 87 capsule.

 

[fsalter]

Bingo!..you found the problem, there definitely is not supposed to be continuity. Happened to me a couple of times.

 

[HosaMogami]

I might have found the issue with figure 8 mode in my mic. Looks like I have continuity between the backplates, and I'm pretty sure there isn't supposed to be any on the 87 capsule.

Did this fix your issue?

 

[Ricardus]

Did this fix your issue?

I won't know until I get the new capsule, but if I had to guess, I would say this is the answer... in my case anyway.

 

[useme2305]

did you even try to clean the space between the backplates?

 

[Ricardus]

did you even try to clean the space between the backplates?

You mean like take it apart or something? I can't tell if you're being serious.

What I did was get with John from Peluso Microphone Labs, who is an acquaintance, and sent it back to him.