Neumann Vintage U87 Clone : Build Thread.

[atticmike]

U fellas know european vendors that sell mounts for the capsule?

 

[tskguy]

http://www.thiersch-mic.de/en/estm_produkte.html

 

[poctop]

if you do a lot of close miking and have external preamps that have tons of gain to spare

I can confirm absolutely correct levels now,my readings have been a 35dB and 46dB of gain pot positions which equal -11db difference to an U87Ai!!!This is exactly what i wanted to see all the time-SPOT ON!

that should not be more than about 10db 
Dan,

 

[firfe]

hello
i've just a little question about transformer.
i'm looking for the better sound
and what 's the best Xtransformer between peluso , ami T13 or cm 2480...
closer than the original.
because there is a big price difference
75 dollars ...peluso
95 dollars ...ami T13
43 dollars....CM 2480
(all without shipping)

thanx in advance

sorry for english.

 

[Marc Duchesne]

Seems like I have the same T13 transfo. issue with black wires at 420ohms. I will do the switch and confirm levels... Glad you found it... Thanks !

 

[Tommy Radonicus]

Thanks Matador. An Interesting and Informative Post. Re : The differences between 2N3819 and 2SK170BL JFET's in the U87 clone circuit.

 

[Matador]

Now it's my turn to posit a question. 

Trying to deduce the polarization scheme of the U87 and how it get's the figure-8 pattern.  If my reading of the schematic is correct, here are the various combinations:

(first off, the front of the capsule diaphragm is always sitting at DC 0V via the pulldown of R6).

Mode	Front Diaphragm |	Front Backplate |	Rear Backplate |	Rear Diaphragm
Cardioid	0V	47V	47V	47V
Omni	0V	47V	47V	0V
Figure-8	0V	47V	0V	47V

So if this is correct, figure-8 is constructed by simply facing two cardioid capsules back to back.  Or translated to how tube condensers work, I could also get Figure-8 to work by raising the read backplate to 47V, and then raise the rear diaphragm up to 94V (which doesn't exist in a U87).

Does this all look correct?

 

[Marc Duchesne]

Yep, effectively there seems to be T13 transformers with reversed color code (compared to http://www.tab-funkenwerk.com/id133.html)  for primary and secondary. I switches the wiring in mine and gained at least 10db on the output, which is enormous. It now behaves like my other good mic's... Excellent !!!

 

[Biasrocks]

Yep, effectively there seems to be T13 transformers with reversed color code (compared to http://www.tab-funkenwerk.com/id133.html)  for primary and secondary. I switches the wiring in mine and gained at least 10db on the output, which is enormous. It now behaves like my other good mic's... Excellent !!!

But not anything like a U87i.

You don't want 10db gain, that would mean the transformer is reversed. You want the 200r ohm side on the output.

The color code may be wrong, measure it to be sure.

See this

http://www.groupdiy.com/index.php?topic=49389.msg641094#msg641094

Regards,
Mark

 

[Marc Duchesne]

@Biasrocks
But not anything like a U87i.

You don't want 10db gain, that would mean the transformer is reversed. You want the 200r ohm side on the output.

The color code may be wrong, measure it to be sure.


Yes, I double checked and I really had 420 ohms on the black wires, making it a 1:10 ratio transformer instead of a 10:1.
How I ended up getting less level as 1:10 config. I don't know. But it is now wired ok.

 

[Hank Dussen]

As I stated before the original transformer measures 58R between the primaries (capsule side) and 1k2 at the secondaries.
With the AMI transformer that's 22R and 435R. (all of these measured in the circuit)

I wonder why that is, and whether it makes a difference...

 

[mukole]

Yes, I double checked and I really had 420 ohms on the black wires, making it a 1:10 ratio transformer instead of a 10:1.
How I ended up getting less level as 1:10 config. I don't know. But it is now wired ok.

I'm not sure if i'm on the right track here,
but could it be that with the transformer reversed we are suffering a loss of signal due to running a high impedance output into a low impedance input?
I'm not sure of how reversing the transformer would affect the overall impedance of the circuit as well as the output impedance of the mic,
would it end up being a higher impedance at the xlr than most mic pre inputs?

 

[Matador]

Reversing the primary and secondary makes a 600Ohm mike preamp input look like a 6 ohm load on the JFET drain.  This is almost the same as grounding the microphone primary, with around 99.1% signal loss.  However this tiny signal then get's amplified
by a factor of 10 through the transformer.  In other words, a 1V signal becomes about 1mV, then 10mV at the XLR connector.

Like I said previously, I'm shocked the microphones were usable at all.

 

[Marc Duchesne]

I effectively had to crank up the pre level pretty high to get some level at all... Output impedance problem yes. I really though I was wired up properly from the AMI color code so I did not suspect this part of the circuit. I am really glad it is fixed now.

 

[kante1603]

Like I said previously, I'm shocked the microphones were usable at all.

Yes,for me it was totally unusable for standard vocal stuff,so I didn't use it and wanted to take care later.....now it's working same as the originals- really!

And because of this I have bought a bunch of B2Pros now here in germany,they're on sale now for only 99 Euros including everything!Have received them yesterday and can confirm that they are the latest generation having enough usefull inside space,same as my first one. ;D

Cheers,

Udo

 

[spudstyle]

Hi everybody,

I just finish my project, everything seems to be ok but i got a big hum (50Hz) noise and i find the output level too smaller. I'm not electronician so it's very hard to find the problem :/
First, i verify all solders and looks good, verify the ground wire, ok... So i decided to disconnect all switch and caps, The same noise ! The noise disappear when I disconnect CM2480 or the B2 pcb (still here but very very low). Cinemag is correctly wired i think: RT = Red, SW = Brown, BL = Orange and WS = Yellow. The noise still present even without the body

Any idea to help me ?

 

[mukole]

Did you get this noise with the Mic body assembled, I had this problem until I installed the outer casing,
I also experienced this when I removed the headbasket. disconnecting the transformer is stopping the noise because your disconnecting the output.

 

[spudstyle]

No, I will try this tomorrow. It's a behringer b2 pro if that can help (not the same version as kante1603).

 

[kante1603]

No, I will try this tomorrow. It's a behringer b2 pro if that can help (not the same version as kante1603).

Hello,

the type of mic housing is not too important as long as it is made of metal.
You should check back if all of  its' parts have a very good contact among each other and pin 1 on the xlr.That means including the basket.
Also the ground connection inside from pcb to the rail is very important.
These measurements should all end up close to zero ohms.
If the problem still exists after that it might be helpful if you can post some pics of your build?

Good luck,

Udo.

 

[spudstyle]

Et voilà, problem solved ! As mukole says, the body must be full assembled to work.
The microphone sound very good but output level is very low compared to the bluebird. That's normal or it's a problem like bad wired transformer ? (see my precedents posts for my transformer wiring)