Neumann Vintage U87 Clone : Build Thread.

[wthrelfall]

I've got the use of a 'scope so decided to calibrate the FET according to Matador's post.  Problem is, when I measure the signal on the drain of the FET, the waveform doesn't really resemble a sine wave anymore, and doesn't respond to R11 calibration the way it should (ie. with the waveform flattening out as amplitude is increased).  I checked my sine wave source on the scope and it's perfectly symmetrical and normal.  Attached is a photo of the waveform I get at the FET drain.

and another one with the time zoomed out.

 

[bezen4uk]

Hi,
There is oscillation.
You need probe with compensation.
Or  measure at transformer out

 

[poctop]

I've got the use of a 'scope so decided to calibrate the FET according to Matador's post.  Problem is, when I measure the signal on the drain of the FET, the waveform doesn't really resemble a sine wave anymore, and doesn't respond to R11 calibration the way it should (ie. with the waveform flattening out as amplitude is increased).  I checked my sine wave source on the scope and it's perfectly symmetrical and normal.  Attached is a photo of the waveform I get at the FET drain.

and another one with the time zoomed out.

have you consider the THD method with the Room capture demo software or the earing method to see how it behave first when you inject the sine tone,  first you could see how it works at a fix voltage to see if the circuits works, let say at 11V to the drain and try it out.
if your are not familiar with the scope sometime the trick is to get the proper level of signal to actually see hat will happen when you twaek the FET if you have too much signal you wont see anything ,  you also have to connect you probe ground to the mic Body or pin 1

hope this helps,

Dany,

 

[saxmonster]

sax-
personally i think the 414 sits better in that mix, the u87 makes it stick out a little odd. but stand alone i prefer the u87.
[/quote

I agree and I think the u87clone has the better sound I will just have to tuck it into the mix a little better. May be a little eq here and there.  Like I said earlier, basically i just popped it in and raised the level untill it sounded somewhat ok.  I was in a rush. But now that i know its the better mic I will do some more tests and comparisons.

Thanks
scott

 

[tskguy]

Poctop,

I sent a paypal payment for a  set of your U87 boards. Its ben about 2weeks and I was wonderin if I should start to worry.
Thanks,
Eric

 

[Matador]

Attached is a photo of the waveform I get at the FET drain.
...
and another one with the time zoomed out.

Is it a high impedance probe?

 

[wthrelfall]

No, I don't think so.

Attached is a photo of the waveform I get at the FET drain.
...
and another one with the time zoomed out.

Is it a high impedance probe?

 

[wave]

Some Short Demos

Please don't laugh as I kinda rushed to do these.  But this is a project I am working on.  I am still working on mic placement and mixing but this gives you an idea of what the mic sounds like compared to an AKG c414, the older kind from the 90's.  I am running both Mics through Slenderchap's  Eee-Zee 1073 clone.  With just a touch of waves C1 compressor.  And true verb for the mix demos.  Like I said still have a lot to learn and figure out mixing, reverbs and mic placements.  Since I was doing everything myself in different rooms I was running around like crazy so there are a few pitch issues but you get the idea. Be gentle.

U87 Clone Dry

http://www.ehornstudios.com/media/U87%20Clone%20Dry.aif

U87 Clone Mix

http://www.ehornstudios.com/media/U87%20Clone%20Mix.aif

C414 Dry

http://www.ehornstudios.com/media/C414%20Dry.aif

C414  Mix

http://www.ehornstudios.com/media/C414%20Mix.aif

Let me know what you think of the U87.  I already have some conclusions.

Well we all have opinions so...
I like the sound of the U87 by itself over the 414 for sure. There's a nice presence and depth to it. I can understand what berkeleystudios was saying about how the 87 track sticks out a little in the mix but I prefer the sound of it. I personally like the rawness of the track. The 414 seems a little too polished for me. Just my 2¢.

Dave

 

[KasperNyhus]

I've got the use of a 'scope so decided to calibrate the FET according to Matador's post.  Problem is, when I measure the signal on the drain of the FET, the waveform doesn't really resemble a sine wave anymore, and doesn't respond to R11 calibration the way it should (ie. with the waveform flattening out as amplitude is increased).  I checked my sine wave source on the scope and it's perfectly symmetrical and normal.  Attached is a photo of the waveform I get at the FET drain.

and another one with the time zoomed out.

Have you tried to activate the PAD? That made my sine curve act as it should... But I don't know why...?

 

[saxmonster]

Figured out more stuff,

On the tightening problem, the sound would go in and out.  I messed with the transformer and I think it was hitting the bare ground wire on the xlr inputs in the transformer box of the 460case.  I fully insulated the transformer covering the ground wire with electrical tape and now it doesn't do it any more. Success!!!!!!!


I also found out that my akg C414 is louder when I swap it with the u87 clone.  I keep the same gain and just switch the xlr cable between the mics.  Why is the c414 louder?  I know they are different mics but the c414 just has a higher out put.  It that because of the differences in the transformer?


Also does anyone know where I can find a 15.6k ohm resistor?  Everywhere I look it seems that I have to buy them in bulk or they are not a stocked item.  I checked all of the usual places.  Can I get a different one.  Maybe a 15.4 or 15.8 would work?  How close do I have to be or does it have to be exact?  Also do I get a 1.4watt resister?  I can paypal someone in the usa if you want to send some to me.  They can be shipped through a letter in the mail right?

Thanks guys

 

[poctop]

Figured out more stuff,

On the tightening problem, the sound would go in and out.  I messed with the transformer and I think it was hitting the bare ground wire on the xlr inputs in the transformer box of the 460case.  I fully insulated the transformer covering the ground wire with electrical tape and now it doesn't do it any more. Success!!!!!!!


I also found out that my akg C414 is louder when I swap it with the u87 clone.  I keep the same gain and just switch the xlr cable between the mics.  Why is the c414 louder?  I know they are different mics but the c414 just has a higher out put.  It that because of the differences in the transformer?


Also does anyone know where I can find a 15.6k ohm resistor?  Everywhere I look it seems that I have to buy them in bulk or they are not a stocked item.  I checked all of the usual places.  Can I get a different one.  Maybe a 15.4 or 15.8 would work?  How close do I have to be or does it have to be exact?  Also do I get a 1.4watt resister?  I can paypal someone in the usa if you want to send some to me.  They can be shipped through a letter in the mail right?

Thanks guys

There is nothing stoppping you from leaving the pot inside the mic,  and also when you measure the pot Value did you measured it out of the board completely or at least lifted the leg in contact with the (Source) pin of the FET ? because it will affect the reading by the DMM this is important  as for the gain of the mic this is perfectely normal as the U87 circuit is not high gain like the 414

 

[saxmonster]

Yes the resistance was the same in or out of the board.  It didn't matter.  I wanna put in a real resistor cause the pot is pretty beat up from shaving it to fit and its really not sitting in there good cause of the short legs and now that its been re-soldered I just wanna replace it with something sturdy.

-Scott 

 

[HellfireStudios]

Saxmonster, you could put two resistors in series whose values added up to the pot's value (maybe 2-7.8k resistors).
Just in case the question arises, series wiring is where you take one lead from both resistors, twist them together, and solder. Then, you would put the two remaining leads in the PCB holes for the original resistor (it might be easier the other way around with this mic).

Series wiring:

----[R1]----[R2]----

 

[kante1603]

Output level on a U87 (1980)

Hello,

I did some search on the net,for those who are interested or concerned about a "lowish" output level check this:

A U87 from 1980 is specified for a sensitivity of 8mV/Pa +/-1bB.This equals arround -40dBu.
A Shure C414 (B**) is at 23mV/Pa,therefore arround -30bBu (for those who must compare apples to oranges ;D).
A nowadays U87Ai is specified even at 28mV/Pa what equals -29dBu.

So-compared to a modern U87-expect to dial in some 10 dB more gain.No biggie for even a standard nowadays mic preamp.
This all given at propper load and so forth.....
I think we can expect this when using the right parts etc.,I´ve ordered T13 and John Peluso´s capsule.
Just some "numbers" to give you an idea.

For those who want to go a bit in-depth here´s a good site from germany (you can switch to an english version on top of the page):

http://www.sengpielaudio.com/Rechner-sensitivity.htm

Have fun with your builds,

Udo

Edit:I forgot to mention that the highest output level on switchable pattern microphones is normally in cardioid mode while omni is lowest!

 

[dirtyhanfri]

Got my boards today, Thanks!

 

[saxmonster]

Question.

If I need a resistor of 15.65 Kohms for this project can i use this one.

http://search.digikey.com/us/en/products/MFR-25FBF-15R8/15.8XBK-ND/4143

It has a 1% tolerence which if i subtract that I get 15.64kohm.  If I have to order 5 of them one has to be pretty close to that.  what do you think?  If not I will try to find two resistor at half the value.

Thanks
Scott

 

[kpearsall]

saxmonster, the resistor you're needing is a 15,650 ohm resistor but the one you posted a link to is 15.8 ohm. Nope won't work!

This is the same resistor series with the proper value.
http://search.digikey.com/us/en/products/MFR-25FBF-15K8/15.8KXBK-ND/13256

Hope that helps

 

[kante1603]

saxmonster, the resistor you're needing is a 15,650 ohm resistor but the one you posted a link to is 15.8 ohm. Nope won't work!

kpearsal is right!
Do some search for resistor in E192,there is a value at 15,6k if you want to get closer.Don´t know where to buy them in the usa because Im in germany,sorry.

Udo.

 

[saxmonster]

I think the link above is wrong as it says 15.8 again.

getting closer

anyways, found this buts it only 100 mwatt will this work even though its not a 1/4watt?

http://ca.mouser.com/ProductDetail/Vishay-Dale/RN55C1562BRE6/?qs=NVJATC80C4%2fyLVR6unXY27%2fCIyKgzlEmBi3LQ5AHdOc%3d

thanks

 

[kante1603]

I think the link above is wrong as it says 15.8

The link seems right,it says 15,8 k(=Kilo!!!) ohms,your first search ended at 15,8 ohms which is a thousand times lower.