Neumann Vintage U87 Clone : Build Thread.

[poctop]

No output issue here ,

i can do a quick test with my original and clone so you can hear a look,
Dan,

Just a side note the AI version the reissue of the mic has about 10db higher output ,
i will try sending a message to odbfs he has built tons of them ,
dan,

 

[Hank Dussen]

I have you checked all the test voltage including the 40V polarization voltage to the capsule it is supposed to be 48V but with non high-Z probe you would get about 40V wich is what you should read  , is your pad shorted ,  how did you bias the FET,
have you checked the FET idss as Matador sugessted before putting it in the mic , 
what is your final drain voltage,  please make sure you have no error on mounting component to pcb ,
i know some of the builder had this problem that would be interestting to know what it ended up beeing the issue ,
so if anyone can chime in as per their mic output situation that would be nice , do you have a scope to bias the FET,
Hope this helps,

Dan,

Kante was so kind to send me 2 FET's. The idss were around 9,5.
I did the biassing with a scope and setting the drain at about 8,5v gave me the best and most symmetrical distortion results.
Setting it higher didn't give a lot more gain.
All the numbers seemed to be OK. The microphone works. Just with a low output.
The pad is not shorted.
i didn't check the 40V polarisation tough. How do i do that?
I'll also re-check the components.

 

[Hank Dussen]

I'm measuring 17,5v between ground and the backplate of the front capsule.
That's probably too low?
What could cause this?

 

[poctop]

HAve you check the basic xlr input conf and tested transformer and orientation. 9.5:1 and also all ref voltage as posted .,
something is definitely wrong here ,  that kills your output , are you in cardiod mode, i would check back the pattern config or remove it and the capsule and check back roll off part of the circuit style , it seems the circuit is driving a lot a current and droping your pol voltage wandering about the Fet remove it and check back voltage at drain if you can get it up to half rail voltage ,
might be a leaky cap , check your zener voltage , you have baised with capsule off right or no cap,
really hope to get in the bottom of this and that will probably help others with the same issue,
Keep me posted,
Dan,

 

[poctop]

Here is what my Clone sounds like the clip is very raw ( No pop filter to have an idea of the proximity effect ) but at same gain setting
D.
https://cdn.groupbuilder.com/groupdiy/u/39511/58d0281993963.wav

Edit : when i say it is very very flat i am tlaking about the extra sweetness with the original capsule.
Got the year october 1979 
Dan,

 

[0dbfs]

The ones I have put together are all consistent with regard to sound and output level. When I first put them together I just set the bias with the (10.5V?) drain voltage method. This was fine and they sounded good. I did end up recording some louder sources (horns and toms) which resulted in asymmetrical waveforms and some distortion which I had not observed with quieter sources. I then went back and revised with the scope method and they no longer do that. I didn't sort any of the fet's but I do have spares and extra's which I ordered from different sources. These do have lower output than some other mic's I have but I consider that an attribute to use in my gain staging and mic selection. For instance, I often mic up acoustic guitars with km184's and may typically use a gain setting of 21-24db on the pre. The u1621's get something in the range of 39-42db of gain on the pre for similar output levels and placement.

I haven't made "scientific" comparisons of sonics or levels. Rather use them and gather my empirical observations by working on the tracks, mixing, and taking a more zen approach to what the final results are on that particular recording/project.

All that said, I do really like having these in my kit and consider them to be high quality tools based on empirical assessments.

I did order a bunch of extra pcb's and intend on making more

Cheers,
jb

 

[0dbfs]

You know, come to think about it I did hook up my output tx wrong on the first mic. It may have had low output and the patterns were not working as expected but it did pass signal. I think I ended up following the pcb traces and comparing against the schematic to confirm proper pinout and that sorted the issue quickly. The way I had it hooked up caused the phantom voltage to be routed improperly and the voltages in circuit were not as expected as a result.

One thing to check as well as the Xlr hookup like Dan mentioned since that could also affect powering the fet and capsule.

From the Xlr trace the phantom through the circuit and confirm the voltages as well as your 48v supply.

Cheers,
jb

 

[firfe]

hello
i've buy 3 U87 pcb.
i've paid with paypal...
should i do something else?
best
jf

sorry for my perfect english....

 

[wave]

Hello gents (and any ladies if present)
Dany can you tell me what the capsule voltages should be if I measure in cardioid, figure 8 and omni?

I'm getting very different sounds from front to back capsule in figure 8 especially. The back side sounds like it has a low pass filter and seems to be a little louder than the front.
I would like to rule out any odd behavior in the circuit before I pull the capsule and have Eric test it (God forbid a reskin)

Thanks,
Dave

 

[poctop]

hello
i've buy 3 U87 pcb.
i've paid with paypal...
should i do something else?
best
jf

sorry for my perfect english....

Nop, i will take care of the rest , Thanks for your order
got your payment will be shipping tommorow
Dan,

 

[poctop]

Hello gents (and any ladies if present)
Dany can you tell me what the capsule voltages should be if I measure in cardioid, figure 8 and omni?

I'm getting very different sounds from front to back capsule in figure 8 especially. The back side sounds like it has a low pass filter and seems to be a little louder than the front.
I would like to rule out any odd behavior in the circuit before I pull the capsule and have Eric test it (God forbid a reskin)

Thanks,
Dave

I checked my specimen over here for the voltage as the pattern are consistent in the 3 modes ,  keep mind that the backside reading are funky because they are not taken with a HZ meter and they are 60M and 1G resistor involved measuring them before those HZ resistor will help but not help troublshooting as the pattern switching is ahead ,but with a normal meter they should look alike when normal , let me know if you find the problem as this might help others as well,

Measurement taken with Fluke 175

 

[wave]

Thanks Dany,
We did trace the problem to a difference in the capacitance between the 2 capsule halves. Eric fixed it and now the mic sounds like hot oiled *******.
Oh Yeah!

Dave

 

[HellfireStudios]

Thanks Dany,
We did trace the problem to a difference in the capacitance between the 2 capsule halves. Eric fixed it and now the mic sounds like hot oiled *******.
Oh Yeah!

Dave

What do hot oiled ******* sound like?

-James-

 

[rmaier]

Slick?

 

[wave]

Slick?

Haha!

 

[scottmichal]

I have a stupid Noobie question.

How do you install the isolation pin? The plastic part doesn't quite fit in the hole. Do I solder it in? That seems like it would defeat the purpose of isolation. Also, I have a single sided capsule and no pads. Should I go ahead and install the headers anyway, or do I need to do anything to disable those circuits?

Other than that, I am having a ball! Got all of the components soldered on, now waiting anxiously for the transformer to come in the mail.

 

[wave]

You just push the turret pin into the hole. No solder! I had to shave a tiny bit of plastic to get it in the 2nd one I built.
As far as the capsule what kind is it? Why is it only one sided? Dany should chime in but you might need to put in a 50pf ceramic between the rear diaphragm and back plate pads (again I'm not 100% sure)
I would put the headers in anyway as it makes it easier to unsolder leads for any troubleshooting you might have to do.

Dave

 

[poctop]

I have a stupid Noobie question.

How do you install the isolation pin? The plastic part doesn't quite fit in the hole. Do I solder it in? That seems like it would defeat the purpose of isolation. Also, I have a single sided capsule and no pads. Should I go ahead and install the headers anyway, or do I need to do anything to disable those circuits?

Other than that, I am having a ball! Got all of the components soldered on, now waiting anxiously for the transformer to come in the mail.

Those pin are pressed fit, normally this is the first part i get on the board first , the trick is to stick the pin in the middle and then push the board hard square onto a hard surface and it will pop in , as per the capsule just leave the Back (diaphrame and backplate) pad as is ,
that will do the trick ,
Hope this helps,
Dan,

 

[Hank Dussen]

OK, I did some more tests.
I did have 40v on the backplate of the capsule after all. There was just something wrong with my DDM.
After double (triple) checking all the components I started comparing my mic to the vintage U87 I borrowed.
This lead me to the transformer. I was pretty sure I hooked it up correct, yellow wires on the cap side, black wires on the XLR side.
Just as on the AMI site. http://www.tab-funkenwerk.com/id133.html
Nevertheless I decided to reverse it and, bang, there was my 15dB of gain!
It should be black wires on the capsule side and yellow on the XLR side!
(at least with my transformer)

My mic levels perfectly together with the vintage U87 now!

But what's more I compared all the components and it appeared there are some small differences between mine and the vintage U87:

The vintage one does not have the caps (C16 and 17) nor the inductors at the XLR. (as in the U87i?) Why were these there anyway?
C6 has the marking 820 on it. But 820pF seems way too high! Maybe it's 82pF?
R9 is 1k2 instead of 6k8
C5 is 0,015uF instead of 0,01uF
R2 is 330k instead of 150k
R11 is 4k7 and there 6,85v @ FET drain, 1,25v @ FET source

In the circuit I measure 58R between the primaries (capsule side) of the transformer and 1k2 at the secondaries.
With the AMI transformer that's 22R and 435R, which seems quite a difference.

Does anyone have some toughts on these differences? They don't seem to be that important but nevertheless they must have done it for a reason.
They do seem to be original. Not something that was altered later.


Pieter

 

[dandeurloo]

I've been using my 87 on a number of things lately and they sound wonderful.  Do what ever it takes to get your builds working.  I used vintage capsules and transformers.  Now I can't wait to get the 67's going!