Neumann Vintage U87 Clone : Build Thread.

Just finished building a pair of these this morning.  I went with the Cinemag transformers and Maiku capsules.  Both work perfectly right out of the gate, which I think is a first for me.  I've only done a basic vocal test so far, but they sound really good. 

One thing I've noticed is that the back of the capsule sounds a little bit darker than the front in fig 8, is that normal? 

C

kante1603 said:

Looking at the schemo you can see why it must be a dual backplate when looking arround the switch arrangement.
So in this (vintage) circuit a dual backplate is a must-have.Only if one decided to just use the cardiod pattern the K67 capsule will work.

Click to expand...

Possibly I am wrong, but it appears if one rewired correctly, that omni would still work with a single backplate capsule.  You would just lose figure 8. 

It is quite normal. What is happening, is that both sides of the capsule are out of phase with each other. As you speak on the other side, flip the phase with your preamp, and they should sound similar.

Colorblind said:

Just finished building a pair of these this morning.  I went with the Cinemag transformers and Maiku capsules.  Both work perfectly right out of the gate, which I think is a first for me.  I've only done a basic vocal test so far, but they sound really good. 

One thing I've noticed is that the back of the capsule sounds a little bit darker than the front in fig 8, is that normal? 

C

Click to expand...

Good to know, thanks!

C

fsalter said:

It is quite normal. What is happening, is that both sides of the capsule are out of phase with each other. As you speak on the other side, flip the phase with your preamp, and they should sound similar.

Click to expand...

Is there any reason to use films for C2, C14, C16 and C17 rather than C0G MLCC's? Wondering because I have the C0Gs in those values in stock but it seems that everyone is using films.

Need some quick help with the connections of a Cinemag 13113 on a taper board.

(http://cinemag.biz/mic_output/PDF/CM-13113.pdf)

How do my Brown, Red, Orange and Yellow translate into the German abbreviations WS, BL, SW and RT?

Can someone confirm this would be the same connections as the 2480 (http://cinemag.biz/mic_output/PDF/CM-2480.pdf)? Or is it turned around?
RT = P+ = Red
SW= P- = Brown
BL = S- = Orange
WS = S+ = Yellow

Ok, looking at the schematic: https://www.gearslutz.com/board/attachments/geekslutz-forum/226308d1300729000-mxl-v67-mic-mods-u87sch.jpg

and the Cinemag CM1113 data sheet, I'm thinking that it should actually be:

RT = P+ = Brown
SW = P- = Red
BL = S- = Yellow
WS = S+ = Orange

Wordsushi said:

RT = P+ = Brown
SW = P- = Red
BL = S- = Yellow
WS = S+ = Orange

Click to expand...

I think it is correct... Check the phase after installing the transformer...

Mine fired up on the first try, though I had the transformer wired out of phase, but once I fixed that... Magic!

I did mine with a 3u Audio Warbler 1 capsule, which is not a typical variant. It has a much smoother top than the usual 87/67, so it was dark. But it takes EQ extremely well. What I noticed with this combination is that it sounds PERFECT for the type of animation and video game character voice over work I get booked for. I mean dead on perfect.

https://www.dropbox.com/s/f3feuh0af9skvek/MYN-87-1.wav?dl=0

Character voice work is often dynamic and very energetic, so I know there's a obvious analog with the type of music some of you create and the sources you record. I haven't heard of anyone using a 3u W1 capsule on Dany's brilliant D87 before so I wanted to report my findings to the group and my thumbs up for the 3u W1. I just happened to have an extra so I used it and was really very pleasantly surprised how incredibly awesome this mic sounds on my voice.

Neutrino said:

Hi,

A quick question:
I had biased my U87 clone for symmetric clipping, but measured a drain voltage of only about 8.7 Volts. Since it sounded fine, I didn't worry too much about it. But in a recent vocal session I had the feeling that the microphone started distorting a bit when the vocal became really loud. Can somebody comment on whether both issues could be related and whether it is an indication that something is wrong in my built?

Best regards,
Waldemar

Click to expand...

Regarding symmetrical clipping, the vocals, the wind instruments and the drums actually have an asymmetric waveform. Would it be better to take it into account when biasing the FET in mic head amps generally?  What would it mean in practise? When the FET gets the initial attack it will make the FET conducting more and drop the drain voltage. So the drain voltage should be a little bit greater than used when biased for symmetrical clipping, right? That way the mic would have more clean headroom for vocals.

Wordsushi said:

Mine fired up on the first try, though I had the transformer wired out of phase, but once I fixed that... Magic!

I did mine with a 3u Audio Warbler 1 capsule, which is not a typical variant. It has a much smoother top than the usual 87/67, so it was dark.

Click to expand...

I've got the same capsule and going to put it into SYT-5 body. However, it's cardioid only capsule, and I would like to simplify the U87 circuit somewhat.

So I'm wondering cannot the capsule be connected to FET gate directly without the 470 pf capacitor using only a single 1G resistor from gate to GND? 470 pf (C4) is there to protect the FET if the capsule shorts (https://groupdiy.com/index.php?topic=35153.0) bu couldn't it be possible to use some other protection  scheme (diode or white LED to GND etc. though that would also add some capacitance I guess lowering the output level).

Hi guys!

After finishing stuffing the (blue) pcb (with polystyryne caps) fully, and mounting them in the 939‘s STY-5 mic, I decided to bias the FET.  So I plugged a XLR with 48V and measured with my black probe to the CGND, and the red probe to the DRAIN. With the blue trimmer pod fully opened, it only read 6,9V instead of the 11,5V everyone here keeps talking about.
I checked for cold joints, but couldn't find any.  Capasitors are all stuffed correctly regarding polarity.  I am totally stuck.  Any idea how to get the bias to the 11,5V?

Add info: zener = 22,5V - R17 =19,83 - T13 AMI with yellow on S and black on P (got the reversed one)

Maybe a faulty trimpot.
Did you check all voltages ?
Please tell us all the voltages which are shown in the schematic on the first page.
The zener looks good so far.

TillM said:

Please tell us all the voltages which are shown in the schematic on the first page.

Click to expand...

Thanks for your help! I opened the Reference Version 16 Schematic, found on the first page. Every point i measured had its minor differences. For instance according to the schematic C10 should be 25V, and I read 19,05V. 
Also between R18 and R19 was measured 45,6V by me (instead of the 48V that was written on the document). I guess this is okay...

The major differences were around C11 (44,8v) , C13 (44,2V) and C7(6,9V), they should be 70V, 70V and 25V, if I am correct.
Reading was done with trim pod fully opened.

Yes r18/19 is totally okay.
Measure the voltage at R14,c7 and c9 and tell us what your DMM shows.
Well as suggested earlier this thread try a 33v zener instead of 24v.

TillM said:

Measure the voltage at R14,c7 and c9 and tell us what your DMM shows.

Click to expand...

You were right, it seems like a kind of similar problem Neutrino had on page 142 of this forum. I am using the same trimmer and a similar IDSS rating as he did. Just like In76d said, I ordered a 33v zener, and a 10k trimmer. They are on its way, so Ill let you know if it will help getting the bias to 11,5V.

The voltages measured to the ground are: R14=19,8V and C7=6,9V
I placed my DMM pin at the bottom of the C9 pins, and they read 43V and 6,9V

Today I replaced the 24V Zener with a 33V Zener-diode 1N4752A DO-41. The good news was that the drain read 8,2V (trimmer fully opened) which was slightly higher then my 6,9, but still not the 11,5V I wanted to have.

In addition, I replaced my 25k trimmer with a 10K ohm 0,5W, as read some pages back.  The drain now went to 3,6V which, of course is even worse then before.

I double checked all components and connections, nothing weird.  The only things I was not sure about: can the transformer be linked to the pcb while measuring, and does it matter which way the trimmer is inserted?

EDIT: I hate to be this guy, but the wires bb and cc made contact with eachother. It was a small solderpin that made contact between them. After I fixed it, I was able to set the bias correctly. Thanks for the help!

hansen said:

EDIT: I hate to be this guy, but the wires bb and cc made contact with eachother. It was a small solderpin that made contact between them. After I fixed it, I was able to set the bias correctly. Thanks for the help!

Click to expand...

Hahaha ... this can happen
I build several 990 DOAs for myself and one never worked, after months of changing the transistor and the inductor I test them and the DOA getting so hot. With more experience you will find the issues.
Cause I know, that my faulty DOAs always getting hot when I made a mistake with the diode.
So in my case, I was searching for two months change parts and so on and the mistake was a Diode in the wrong direction.
So you learned also a lot with your U87

If, in a hypothetical world, I wanted, for some crazy reason, to have a bit more low end, which capacitor(s),  would I swap from the standard BOM to achieve such madness?

Had read in this thread c5 , increased will increase bass, c6 to say 330 pf may help as well, that’s the high cut cap.