Neumann Vintage U87 Clone : Build Thread.

[Cgaines]

Hello all,

I still seem to be having a grounding issue somewhere that I can't find. I did notice today that before I apply phantom power, I can hear the hum. I thought it might be my preamp but I checked it against some other mics and it didn't hum. I am literally out of ideas... Can someone smarter than my point me in the right direction?

Is your mic body painted?

if you are getting it without 48V applied it's not the electronics.

Try holding the mic near sources of emf like a lightbulb or something. If the hum get's louder and you can change it be reorienting the mic it is likely a transformer issue where the transformer isn't humbucking properly. I have had these issues where the trafo had shorted windings and was able to measure the DCR of the various windings to confirm they didn't match where they should. Which transformer are you using?

Thx,
jb

I'm using the AMI T13. I've used their products in other mic mods and loved them. That's why I went with this route again.

 

[poctop]

I have 9 sets Left as of today.
Dan,

 

[Marcocet]

Hey Matador,

Are you by any chance closer to determining an "ideal" Vp and IDSS are for this circuit? I have a bunch of fets which I'm now capable of testing, but I'm not sure exactly what it is I should be looking for. Thanks again for all your help!

 

[bigswole]

Im about to start stuffing this board, i was wondering could i use the behringer B2 capsule to test the circuit once it is done?

 

[HellfireStudios]

Only in Cardioid. Hook the front diaphragm to FC CAP. Hook the backplate to FC BDY. Leave the other capsule connections unsoldered.

-James-

 

[micaddict]

B-2 Pro has a dual diaphragm FWIW.

 

[kante1603]

B-2 Pro has a dual diaphragm FWIW.

That is correct,but no seperated backplates.
Just take one front connection of your choice and the backplate wire,should work for checking.

Udo.

 

[micaddict]

That is correct,but no seperated backplates.

Interesting, Udo.
I actually made my remark because I thought this might be about the old B2 (without the Pro suffix) which was cardioid only and not multipattern (dual membrane) like the Pro.
From what I know, the Behringers (B-2 Pro) have a 797 Audio, 34 mm, K67-ish capsule. Dual diaphragm, obviously (to enable variable polar patterns). But a single backplate would mean it's partly K47, so to speak.
Guess it's about time I actually opened the heads on mine
Excuse this short hijack.


Henk

 

[kante1603]

Hi Henk,

no prob.Meanwhile we have seen so many different B2 versions that really nobody knows everything about them.If it it a just-cardiod capsule you can use it for checking too of course.If you can measure capacitance it should be roughly around 50pF or so,no biggie.

Have fun,

Udo.

 

[HellfireStudios]

That is correct,but no seperated backplates.

But a single backplate would mean it's partly K47, so to speak.
Guess it's about time I actually opened the heads on mine
Excuse this short hijack.


Henk

A single backplate the B-2 is most likely not. The backplates are probably machined seperately and placed together much like K67. The backplates are probably NOT isolated from each other like in the K87 capsule, which is necessary for proper function in the vintage U-87 circuit. This seems to bring a lot of confusion to this project. I wonder if there is a way to make it clear on page 1...

-James-

 

[poctop]

This seems to bring a lot of confusion to this project. I wonder if there is a way to make it clear on page 1...

It is indeed in the Read this First Manual Tips and Considerations,
Dan, 

 

[HellfireStudios]

Sorry, I forgot the slightly sarcastic emoticon at the end of the sentence....

 

[poctop]

Sorry, I forgot the slightly sarcastic emoticon at the end of the sentence....

No Worry,  as per your advice i did added some connection Picture and a bold note before the capsule section to mention this need ,

Dan,

 

[micaddict]

Wait a minute, is the mere isolation in the K87 vs. K67 what this is all about? (I do know about the difference.) Somehow I translated Udo's "no seperated backplates" as "single backplate". No wonder I was confused.
If that is the case, forget everything I've said.  :-X

 

[Matador]

Hey Matador,

Are you by any chance closer to determining an "ideal" Vp and IDSS are for this circuit? I have a bunch of fets which I'm now capable of testing, but I'm not sure exactly what it is I should be looking for. Thanks again for all your help!

That's hard to answer definitively.

As I said before, lower IDSS/VP will provide more gain with the standard stuffing options.  So if you think the mike is too quiet, you want to find the lowest IDSS JFET in your stash.

However more gain means less headroom:  if you are close miking very dynamic sources you might need more input headroom and less gain.  In those cases higher IDSS will give you more input headroom (meaning the capsule can supply more voltage before the input stage overloads).  This holds true until about 12mA of IDSS, then other circuit tweaks become necessary.

So a JFET with an IDSS of about 9mA will give about 200mV of headroom, and about 31dB of gain.
A JFET with 11mA of IDSS will give about 260mV of headroom and a gain of about 29dB.
A JFET with an IDSS of 2mA will have about 125mV of headroom and a gain of about 36dB.

This applies to the 2N3819 of course.

In my stash of 100 JFET's, I've found exactly three that were less than 3mA IDSS.

 

[HellfireStudios]

Too bad no one can check an actual Nuemann FET's IDss for a conclusive answer to this question...

-James-

 

[atticmike]

Could somebody make an estimate on how much a single mic would cost with the cheapest capsule (the one for 109 bucks)?

 

[HellfireStudios]

Could somebody make an estimate on how much a single mic would cost with the cheapest capsule (the one for 109 bucks)?

There are far too many variables in your equation to reach any sort of total. The donor body you choose will determine which switches are easily accessible, and how close the headbasket/capsule interaction will be to the original. The cheapest is not necessarily the best choice for these reasons. The type of capacitors you put in the mic will influence the price (to a much lesser degree). Any unfinished or engraved mics that you may wish to paint will need to have the primer/paint/clearcoat budgeted in as well. There are plenty of other places to spend money too (a better shockmount comes to mind). As you can see, it is best to find what donor mic fits your needs, and go from there.

-James-

 

[Marcocet]

Thanks Matador. I guess what I'd like to do is make a collection of figures, and then extrapolate functions for the headroom and db, which both seem to be logarithmic, or at least close to logarithmic, and find if there's a high point. Any chance you've kept records of those 100 fets you've tested? I know, it's a lot of leg work so don't feel pressured to share if you'd rather not. Thanks for all the help so far!

 

[atticmike]

Could somebody make an estimate on how much a single mic would cost with the cheapest capsule (the one for 109 bucks)?

There are far too many variables in your equation to reach any sort of total. The donor body you choose will determine which switches are easily accessible, and how close the headbasket/capsule interaction will be to the original. The cheapest is not necessarily the best choice for these reasons. The type of capacitors you put in the mic will influence the price (to a much lesser degree). Any unfinished or engraved mics that you may wish to paint will need to have the primer/paint/clearcoat budgeted in as well. There are plenty of other places to spend money too (a better shockmount comes to mind). As you can see, it is best to find what donor mic fits your needs, and go from there.

-James-

Not trying to be sarcastic but couldn't you just put a switch inside the body and drill a hole through the body?

May not look that fancy but it serves the purpose of doing three characteristics without affecting the quality, just that silly switch popping out?