Neumann Vintage U87 Clone : Build Thread.

[Mickey Free]

Hello,

can't remember what board you are refering to.
But it's easy,the goal is just to get the switch pins ungrounded and not connected to each other while the front pins (those connecting to the swich housings etc.) must have a good ground connection.
Ohm them out and cut traces as needed.

Best,

Udo.

Thanks Udo. It is the Behringer B2 Pro switch from the newer model. I'll try to follow your advice, thanks!

 

[kante1603]

Thanks Udo. It is the Behringer B2 Pro switch from the newer model. I'll try to follow your advice, thanks!

You're welcome.
Remember there are quite a few models of this mic existing,even amongst newer ones.
You can compare your switchboard to mine if you want,I made a PDF on how to prepare it,look here:

http://groupdiy.com/index.php?action=dlattach;topic=48030.0;attach=12800

If you are unsure feel free to ask here.Some pics from both top and bottom might be useful then.
But at least remove all other parts,this makes it easier to work on the pcb.

Good luck and have fun,

Udo.

 

[Deepdark]

Hi guys

I got into trouble calibrating my d87. The max voltage I get when adjusting R11 is 6,7V. I test several point such as my phantom (45,6V) Zener (23,2V) the primary of the cinemag is 45,6V, and secondary is 0V, C15 (4,0V), FC is 4,0V and it should be 40V. The trafo and switches are connected but not the capsules. Is it that who can cause the low voltage?

 

[Deepdark]

Arghhh. The center pin of the fet is broken. Is that this that cause the voltage trouble?

 

[Deepdark]

Anyone else? Could it be the broken center pin of the fet causing the calibration trouble? 

Thanks for your time folks

 

[kante1603]

Anyone else? Could it be the broken center pin of the fet causing the calibration trouble? 

Thanks for your time folks

Hello,

a (mechanically) broken fet is causing trouble while calibrating it???Strange!!!
Once I had a mic without a capsule and it didn't work either!!!......................
..........(Sorry,couldn't resist ;D).

Seriously,swap that fet out first and try to calibrate it.
Phantom and divider voltages (top of zener) look correct so far.About the other readings I can't tell atm,but wasn't it something like 40 vdc at the front backplate capsule connection?Don't have the schematics handy here,but I think I remember it was not the fc connection as you describe.
Measuring there is not easy anyway because it is in the high impedance part.
So swap out the fet first and try.

Best,

Udo.

 

[eastwinds]

Hello folks.
i've just finished a Mod'n'Mic DIY U87 build. I will upload some sax sound samples soon comparing it with my AT4033. but first I'd like to solve the 'no figure of 8' problem that a few builders have been having with this kit. has anyone had this problem with the poctop circuit that's finished a non M'n'M build? There is no isolation between the front and rear back plates on my MK87 capsule, is this the problem?
i rewired the low cut and pattern selector switches, they are working fine now, and are not the problem.
thanks for any suggestions folks
apologies if this is already covered in the thread...it's a long read! 
Ian

M-87 body
PCB D-U87 by Poctop
capsule MK-87
transformer Cinemag CM-2480

 

[kante1603]

Hello and welcome to the forum.

Isolated backplates are imperative in this build when you want all patterns.

Best regards,

Udo.

 

[eastwinds]

Aha! thanks Udo. that explains it then. are there any other builders on this forum using the MK-87. is this normal for this capsule or do i have a dud?
Udo, do you know if there would be any other implications of using a non isolated back plate? would it effect the sound/frequency response/output level of the omni and cardiod settings?
many thanks, Ian

 

[kante1603]

Hello,

I don't know this MK87 capsule,but normally they do have isolated backplates.
Non-isolated would be more like a K67 which are used in an U87Ai (the newer) version.
Are there specs to read somewhere or can you ask your supplier about it?
Or look at the wires,are there three already attached or is there a provision to have a fourth on the capsule?
If the backplates are really not isolated you can run it in permanent cardioid mode of course.

Best,

Udo.

 

[eastwinds]

hi Udo
this is a new French company. Mic'n'Mod....we are very happy in Europe that we can now avoid paying import duty! 
there is some info on the Mic'n'Mod website. i can't copy and paste it so here's a link  :-[
http://micandmod.com/theshop/en/capsules/29-microphone-capsule-mk-87.html
according to their blurb it's designed for 3 wires yet as a k67/k87 backplate omni/cardioid/fig8a so all a little contradictory.
there were wires attached to the front and rear diaphram centres with two addditional wires for attaching to the backplates.
i've been in discussion with the supplier Yannick, he suggested i post on this forum to try and clear up these issues.

so it seems to me like there's been a mistake. these are indeed k67 style capsules and not K87. would you suggest i remove one of the 4 wires? my main concern is that i'm degrading the quality of the omni and cardiod response somehow, though they seem to work. do you think that is likely?
thanks for your help Ian

 

[Deepdark]

Haha kante, do the mic Will work without xlr cable hooked to it? joke seriously, yes it is supposed to be 40v. Hope that it's just the fet that causes that trouble

 

[kante1603]

Haha kante, do the mic Will work without xlr cable hooked to it? joke seriously, yes it is supposed to be 40v. Hope that it's just the fet that causes that trouble

Hi deepdark,

"...it is supposed to be 40v...",I don't get which connection you mean.
It should be the front capsule's backplate (or "body"),not the front capsule connection (or "fc" or the front capsule's diaphragm).

Let's see how your new fet works,o.k.?

Good luck,

Udo. 

 

[kante1603]

@eastwind

Hi Ian,

yes,have found their homepage meanwhile.
From their k87's specs at the bottom of page I can read that it should have insulated backplates.
So it should be the right capsule to get all three patterns.
Their page is a bit confusing,seems they mix up k67 with k87 and the corresponding microphones.
To clear this up a bit:Neumann first introduced the k67 capsule with connected backplates (e.g. For the U67).Later they introduced the U87 which had a k87 capsule with isolated backplates,so four wires.Finding that there's no practical advantage with the isolation Neumann then followed up with the current U87Ai version in (if my brain serves me well ;D) 1987 or so.They use the k67 capsule again,so just three wires because of the connected backplates.This (current) mic has a bit more output level due to some changes in circuit,especially by implementing a dc/dc converter.
Technically a k87 and a k67 are identical,the isolation is the only difference.
Btw.,therefore it's easy to turn a k87 into a k67:Just connect the plates-done.

But what we have here is the vintage circuit that needs this isolation.
Are you sure your capsule's backplates are connected?How did you measure it (continuity check or resistance in ohms)?
I also wonder why your supplier has put in two additional wires.
Do you have access to a capacitance meter?Each front (diaphragm) measured to its' backplate should give you a reading of roughly 50pF.

If the plates are really connected then you can only use one side of the capsule in permanent cardioid mode,so only two wires going to fc and body(backplate).
A little advantage is that you can test which side works or sounds best for you,most of times they're not perfectly the same so will have a slight difference soundwise.

Hope to have helped,let us know,

best,

Udo.

Addendum:

Found this some minutes ago:
http://groupdiy.com/index.php?topic=53177.msg687708#msg687708
Can somebody tell me what's going on here?
Why must I jump between two threads although it seems to be a known issue?
Don't get it.......anyway,what I can say is that I have built four of these mics already.
I used pk87 capsules and must state clearly that in figure eight mode the side rejection is absolutely outstanding!
This leads me to a mk87 capsule related issue,not Dan's pcb design.
Really curious now how this works out!
So I'm sorry,but it seems you will have to wait until this is cleared up Ian,as said I don't know this capsule.

 

[eastwinds]

thanks Udo, that's very interesting. i did a continuity check and have also made a capacitance check now at your suggestion. 400pF on the reverse and 490pF on the front (0.4nF and 0.5nF)...wierd. no isolation yet omni works OK...
i'm going to contact Yannick again about this, i'm not sure why there's two threads going on this...you've made it clear to me this is a capsule issue, not the circuit.
thanks very much for your help, Ian

 

[kante1603]

thanks Udo, that's very interesting. i did a continuity check and have also made a capacitance check now at your suggestion. 400pF on the reverse and 490pF on the front (0.4nF and 0.5nF)...wierd. no isolation yet omni works OK...
i'm going to contact Yannick again about this, i'm not sure why there's two threads going on this...you've made it clear to me this is a capsule issue, not the circuit.
thanks very much for your help, Ian

O.k.,

the values don't seem correct for in this application,maybe in others....
One last check you can do is to measure capsule backplate isoltion in ohms,not with a continuity checker.Just to be safe if there is an isolation or not.Omni might work somehow,but figure eight won't then.

Best,

Udo.

 

[mica]

I just finish assembling my U87, but didnt do the FET adjustment as described here. Can i do it with everything attached, or do i have to remove connections to the capsule and the trafo?

 

[kante1603]

Hello,

best to lift the capsule connections,transformer can be left attached.

Best,

Udo.

 

[eastwinds]

thanks Udo, i did indeed do this test also.
Yannick at Mic'n;Mod has just informed me there was a mistake, his capsule is in fact a K67 type. this explains the anomalies. so i'll live without fig8 for now. anyway he's hoping to get an isolated version made....
This is looking quite good for us European based builders - lot's of capsule choices 
thanks again for the advise Ian

 

[Deepdark]

Just to be sure, I install the 72-T93XA pot on my taper pbc (v1.2). I cut the pin number A (the one opposite to the trimmer) and keep pin B and C. Is it allright or do I cut the wrong pin? I wanna know too if I install it in the right direction. Thanks folks