[sr1200]

This relates to my earlier post about biasing... so, if what you're saying is correct then im going to need to find a new scope... I had to do the bias by ear since my scope died a few months back and i haven't yet replaced it. Hell even 3 or 4 dB would be a vast improvement.  Although I do like the prospects of an additional 6 as stated above...

[kante1603]

So how many of you guys used a scope to bias your fet?

I did-as well as some others here....

Im also a bit blown away by everyones need to try and get more gain, I just did a session with my u87 and had zero problems getting a nice level.

It´s not everyone´s need,it´s mainly mine (and some others who  wrote about a "lowish" level without defining anything).
If you had my mic you wouldn´t have had any problems too-but only when recording in the middle of a punk band!
It is getting on my nerves now that I always must repeat that my mic has not the correct out level and doesn´t meet the Neumann specs
I am working on it,but for getting the level up,not for creating an "A" version of it....
I know both of them,I work with the "A" nearly daily and I worked with the vintage version from the early/mid 80´s on.

[kante1603]

E, If your mic has any more gain than mine does it's no wonder you didnt have a problem.  When you have to crank a 70 db pre up to 9 or 10 to get a decent input level, its an issue.  The mic sounds awesome, theres no argument there, just could use a little LESS head room lol.

Exactly!

[tskguy]

Didn’t mean to add salt to the wound,    I was just sharing the fact that Wave and I noticed my mic had noticeably more gain than his. We both thought it could have been the biasing method.
I wish you luck in troubleshooting your issue. 
Eric

[wave]

So i should probably chime in.
Eric is correct we did need more gain out of hi 9K preamp when doing our A/B comparison. Also, I did the listen method and he did the scope method.
That being said, when I initially did the listen method, my drain voltage was at 12.1 V.
Since I had the problems I stated earlier with the volume drops I changed the drain voltage to 11.5V on the advice of Dany.
Since the mic worked and sounded good I haven't gone back to re-bias yet as my philosophy is "If the car isn't broken, don't fix it".
No I'm def more of a musician than a technician so I don't know if having the .6V difference (between when I "biased the FET to 12.1V and when I changedit to 11.5V) would equate to the actual gain being that much different.

I have noticed that now that the front side of my capsule is wired up correctly (I still feel like an idiot for that one) the mic is experiencing no volume drops or pops or thunder sounds. In fact, it is sounding awesome.
We will have some more techinical opinions after tonight as I think Eric will be by and we can set our mics up side by side into matching 9098 mic pres.

More to come

Dave

[sr1200]

I cant wait to hear the results of the side by side.  IS there a way to calibrate just using a DMM?

[kante1603]

Didn’t mean to add salt to the wound,    I was just sharing the fact that Wave and I noticed my mic had noticeably more gain than his. We both thought it could have been the biasing method.
I wish you luck in troubleshooting your issue. 
Eric

You can see my Reply #305,the last two pics,this shows how it looked like when I biased mine.

Udo.

[kante1603]

I cant wait to hear the results of the side by side.  IS there a way to calibrate just using a DMM?

Hi,

Sadly I don't think it will work.We are looking for clipping points meaning the points when the waveform changes from a perfect sine to more rectangular,exactly when it starts to flatten out both on the positive and the negative side of it.
A normal dmm can not "see" this.
Maybe  you should try to get a scope as a plug in for your computer or an iPad or so?This is a cheap way to visualize the procedure.I did some general scopings with my iPad set into an i/o dock.Seemed to work pretty good.Didn't do this on my build so far because I have a real scope.I think I will check it too when I get back to my mic,I bet it works.

Hope to have helped,

Udo.

[geekmacdaddy]

"how the U87 is made" Though some of this rudimentary, still very cool...  http://www.youtube.com/watch?v=cvtjHhtxmpI&feature=related

[HellfireStudios]

If anyone is building a U87 clone and wants a capsule, I have two spares of what I'm pretty sure are the RK87 capsule. They're brand new and come in a little plastic container.

Pretty sure? How do you not know the origin of the capsules?

[poctop]

if it is a rk87 the 2 backplate will show open circuit noit a short .

Dan,

[HellfireStudios]

Enchilada, I meant no offense. The wording just put up a red flag (modern marketing made me this way). I just want to make sure no one here gets screwed over by symantics.

Unfortunately, that is the k67-style capsule, and they won't work with this project. On the other hand, the U-67 PCB that may be in the works would definitely work with those capsules. The U-87A is also a canidate. Not to mention almost any mic that uses the K67 style capsule (and there are a lot). I hope you can unload your unwanted capsules.

-James-

[kante1603]

My understanding is that not all U87 mics had isolated backplates. Also, the U67's has 6 micron diaphragm. These capsules are 3 micron.

That's right,only the vintage versions had them until 1986.By introducing the U87A(i) Neumann went back to the k67 capsule,they found that the isolated version doesn't give a real improvement.They're the same acoustically,Neumann stated this at least.

Udo.

[geekmacdaddy]

Here's what I have so far. I am officially tskguy's first customer of his K87 clone. Arrived yesterday, and as you know, the biggest hurdle in the financial part of this deal. I have the missing components for the board. To my ears, this is the best sounding capsule replacement, and the clips posted were with the cinemag. My brain tells me that pairing this capsule with the Tab Funkenwerks would be a few degrees closer yet still, but, I have this chinese C12 clone here that is begging for the upgrades as well....2 cinemags for the price of 1 tab.....grrrr.....sucks being poor. Anyway, in the words of Grand Funk Railroad, "I'm getting closer to microphooooone".

[kante1603]

Cool brother Geek!
Yes,this money thingy hurts at the moment,but wait until it´s done because you´ll have a  2 to 3 thousand dollar mic soundwise.Not bad at all
May I suggest you to run the 4 interconnecting wires ("A to AA" etc.) at the bottom sides of the pcbs and solder from top;this way the build will be even "cleaner" I bet,and you´ve got a lot of room to run the capsule wires without touching anything then.
I will do so on my next one.
Nice headers btw......

Udo (BOTSF).

[geekmacdaddy]

May I suggest you to run the 4 interconnecting wires ("A to AA" etc.) at the bottom sides of the pcbs and solder from top;this way the build will be even "cleaner" I bet,and you´ve got a lot of room to run the capsule wires without touching anything then.
I will do so on my next one.

Indeed you may, BOTSF Udo. And thank you! I shall do exactly that. Am I correct in understanding that if the screws ground the boards properly, I don't need to mess with pads CGND and GNDLINK?

BOTSF Jeff

[kante1603]

Indeed you may, BOTSF Udo. And thank you! I shall do exactly that. Am I correct in understanding that if the screws ground the boards properly, I don't need to mess with pads CGND and GNDLINK?

BOTSF Jeff

Exactly,you can see this easily when measuring continuity among all grnd points including the mounting holes.
In my case I had to widen up them with a drill - which opens the continuity to ground-because the pcbs didn't fit the B2Pro and ran a (thick) wire for grounding to the rail.
As long as you can attach/screw them to the metal rails everything is fine.

Cheers,

Udo.

[poctop]

I am working on these and almost ready to try this  ,  I have the BV12 From Max pined In but no tranformer yet ,  but also would like to include AMIT67 Package 
This is crazy packed up but maybe i would be able to free some room between component and ajust size for braketing, thinking about a standard size available mic body ?
Just wandered if anyone would  recommend an standard fit into available body for the next step,  I hope there is room for expansion 

I hope to have mange enough room for Big PIO at tube Height 

Oh By the way..... I really hope it works !


D67 transfo,   D67 socket ,   Du67,    really need to go sleep now
Power:


Transfo PCB:


Socket PCB

[berkleystudios]

Dan my mouth is watering for that u67. will have to pic up a few boards later.

[mrcase]

awesome!

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