Neumann Vintage U87 Clone : Build Thread.

[TillM]

Look at the orientation of the k170.
Don’t have it in mind, but maybe be drain, source and so on are on other pins than on 2n3819.

Edit: drain,gate and source are the same.
How is the voltage at your zener ?

 

[Haoxian]

My zener diode has a voltage of 23.3
I have carefully check sk170 and 2 n3819 their specification, G/D/S is right, I once again to adjust the R11, to increase the voltage again to 11.5 V, current 10 hours continuously, now found that it is broken, only 5.8 V, adjust the R11 has no effect, because it has a maximum.
I really want to solve it, because I have changed the FET five times, and I can't find the answer :'( :'( :'(

 

[TillM]

My zener diode has a voltage of 23.3
I have carefully check sk170 and 2 n3819 their specification, G/D/S is right, I once again to adjust the R11, to increase the voltage again to 11.5 V, current 10 hours continuously, now found that it is broken, only 5.8 V, adjust the R11 has no effect, because it has a maximum.
I really want to solve it, because I have changed the FET five times, and I can't find the answer :'( :'( :'(

Than change the trimmer.
The trimmer must hold the resistance, when you trim him to 11,5v.

 

[fsalter]

I have just finished a D87 with what i am sure is a rotten 2N3819 jfet.  Since Mouser does not carry them anymore, i bought a bunch off eBay, but i am sure they are off spec. Although i adjusted the trimmer to 11.5v ( had to turn the screw almost to the end), the output is very low and is very noisy. When trying to bias with an oscilloscope, i could'nt even flatten out the crest of the sine wave.
Do you know of any suitable substitute for the 2n3819?. I have some J305's, J113's ,PF5102's. Thanks for your help.

 

[Eitan25]

I'm having a similar issue  to Hoaxian and fsalter. Trying to bias the FET, but the maximum I'm getting with the trimmer maxed out is around 7.5V. I tried several FETs (I got a pack of 10) and also tried swapping out trimmers. I'm thinking something along the path has gone awry but I can't figure out what it could be. The solder joints all seem fine, wiring is all correct, zener voltage is reading 23.1V (does that even matter?).
Is there anything in particular I should check for that I'm missing? Did I just get some dud FETs? I got the FET's from ebay because mouser doesn't carry them.

Thanks in advance for any help you can offer.

 

[TillM]

I think j113 should also work, but it’s another pinout. 2sk170 could work.
Look for the same pinout like the 2n3819, cause it’s easier. Then look how it sounds.
Or take a BF244C, the specs are similar to the 2n3819. You just have to swap it 180 degrees.
Give it a try.
Mostly the China 2n3819 seams to have a problem, that’s my expirence.
That you can’t reach 11,5v is strange, did you check the other voltages ?
On the first page is a schematic with typical voltages.

 

[Eitan25]

Thank you for your most helpful reply, TillM! You've opened up some avenues to explore. You're awesome!

 

[jordan s]

I just wanted to say that I recently went through so much trouble with my KM84 build using a Chinese 2N3819 from ebay. I put the transistors on my tester and it didn't even test as a fet. I bought some new ones through Small Bear and the mic works perfectly now. Don't trust those Chinese ebay 2N3819's, they are something else that got the wrong part number printed on them.

 

[fsalter]

I'll second that. Bought some supposidly Fairchilds recently, and they did'nt test as JFET's either. If any one is interested, i found some legit NET312 2N3819's locally. I have a bunch to spare. Their Idss measure between 5 and 8.5 ma.PM me if interested.

 

[SparkleBear]

Hey all,

I've recently built a D87 into one of chunger's SY5 bodies using a t13 from AMI and a thiersh reskinned Neumann k87 capsule. I am having issues getting it functioning. I am not getting anything but strong white noise and very little source signal. I've checked and double checked all of the connections, resoldered all of the joints and cleaned meticulously. I tested with another capsule with the same results too...

Here are my voltages in cardioid switch position:

Front diaphragm 0 v
Front Backplate 40v
Rear diaphragm 5v
Rear Backplate 6.5v
AA - 44v
BB - 0v
CC - 40v
GG 4v
R3 - 6.5v
R1 -  0v
LowCut points 40v
Hot and cold at XLR 47v

transformer pad 1 - 4v and drops
transformer Pad2 - 0v
transformer pad 3 - 47v
transformer pad4 - 47v

At diode 23.24v

It sounds like there is a TINY amount of source signal coming through the circuit but even then there is only high end present, no bass or mids... Ive been banging my head against this project for days. Anyone have any clues?

Thanks a ton for the help!

Eric

 

[TillM]

Sounds like a bad FET to me.

 

[SparkleBear]

Hey all,

So, it was definitely a bad FET. I got it all sorted out with buying FETs from Jameco Electronics. Thankful it was just a simple fix like that... I have about 9 more FETs if anyone else needs one.  PM me...

So, cardioid works perfectly... but seems that in any of the pattern positions I get a cardioid response. The rear capsule does not seem to be injecting any signal into the headamp... Not sure why, I tested continuity with the backplates/diaphragms and the pads on the PCB and all is connected.

The voltage on the rear backplate is measuring at about 6.5v where the front backplate is 40v. Is that correct because of the voltage dividers in the circuit? Im not totally certain about anything here...

Any ideas?

ALSO, I've seen two different FET bias points spoken of here. One at 10.5v and another at 11.5v. Which is the correct point?

Thanks!

 

[TreyDay]

Hello,

A few years ago I bought a U87 diy mod from mic&mod located in France and been using it ever since. (still a total newbie!)

I'm thinking of upgrading the capsule to a higher quality, any one got some suggestions (max 200e)
I found Maiku k87, any one got experience with this capsule?

My mod u87 has a CM-2480 transformer, is it recommended to swap this to a CM13113?

I'd be best if the re seller is located in Europe.

 

[Eitan25]

I want to thank everyone who responded to my questions and helped me out. I ended up finding legit FETs and was able to bias the FET to 11.5V. Now the mics work (I built a matched pair). I was concerned with the low output at first, but I read through the thread and then had an opportunity to A/B test my mics up against an actual 30+ year-old vintage U87, and the output level was the same. So I am relieved and grateful for your help.

Now I still have 2 questions:
1. I know the output is meant to be this low, but if I wanted to modify it to increase the output level, how would I go about it? Is it the transformer? Increasing/decreasing the FET drain voltage? Swapping another component?

2. I did not remove pin 3 of the potentiometer. I just forgot to do that. But my readings were fine and the mic works. So my question is, what kind of difference would cutting the pin vs. leaving it in make? Is my FET bias reading lying to me because the pin is in? Is it necessary or advantageous to go back in and cut it?

Thanks again!! Cheers!
Eitan

 

[HosaMogami]

Does anyone have a Mouser Part# for the 3 switches used on the Switch PCB. I forgot to order mine with the PCBs from Danny, and I have some other stuff to order on Mouser anyway so I was wondering. Any info would be helpful! Thanks!

 

[Colorblind]

Does anyone have a Mouser Part# for the 3 switches used on the Switch PCB. I forgot to order mine with the PCBs from Danny, and I have some other stuff to order on Mouser anyway so I was wondering. Any info would be helpful! Thanks!

Did you order a body yet?  Chunger's SYT-5 bodies come with the switches IIRC. 

 

[HosaMogami]

Did you order a body yet?  Chunger's SYT-5 bodies come with the switches IIRC.

I initially had planned on getting the bodies from him, but he's been out of stock for so long. I found the same bodies from a seller in the UK and got them but they did not come with switches.

 

[SparkleBear]

Dany sells a switch kit on his website... I believe it's for the same pieces.

www.vintagemicrophonepcbkit.com/orders.html

Drop down the d87 menu and it's on the bottom...


Also,  going back to my last post... did anyone else have problems getting the back diaphragm working with their build? Front sounds amazing but the other patterns don't seem to sound at all different from cardioid..

Cheers!

 

[hansen]

I initially had planned on getting the bodies from him, but he's been out of stock for so long. I found the same bodies from a seller in the UK and got them but they did not come with switches.

Me too! I am waiting for ages. I am asking for a shop here in town, that is able to lazer the mic patterns, but If you have an alternative seller in the UK, that has the exact same SYT-5 gen 3  bodies, I'm interested. Could you give the link maybe?

 

[mhelin]

The 2N3819 orientation on the D-87 (L&T) PCBs is incorrect, or at least opposite to the one on U87 schematics (SOLDER SIDE VIEW!) and on some datasheets other than Fairchild's (at least Onsemi, Vishay and Temic agree with Neumann, Fairchild and Central not). How can you test it? Does it matter?