Neumann Vintage U87 Clone : Build Thread.

[saxmonster]

Udo,

The surrounding conditions are in my project studio /  office where I do most of my recording.  I have used the mic in here before and have done many things in here with other mics and never had a problem.  I have not changed anything in the room either.  I have also run an xlr into the next bedroom with is a dead space and still the popping continued. 

I have tried the mic in different preamps and still get the sound.  I even tried the preamp on a mackie at the school where i teach and it still had the problems.  I have used different wires and cable too, different channels.

The gain is set between 2/3's to 3/4 on the mackie 1604.  Doesn't matter if I give more or less gain the sound still stays consistent in ratio with the s/n ratio of the mic as it gets louder or softer.  I have the headphones plug directly into the mackie and the vol is about halfway up. 

When I switch the hpf the sound is still there too just a little less bass, hahhahahah.  And the -10db switch helps but I can still faintly hear it in there.

Its seem that when the mic is cold it doesn't do it until it warms up.  I will have to check that later though. once its cold again.

Thanks for all your help.
-Scott

I put a new fet in and its doing the same thing, so I put the old one back in, hahahaha.  I just don't remember hearing the sound before so I don't think it was always there.  And this was the first I used the mic since i baised it two weeks ago.  What supplys the phantom power to the mic.  Becasue of the non consistent noise maybe its releated to that?

I hope this can be fix, getting nervous, I am sure it can be

Hi,
Please let us know a bit more of the surrounding conditions.
As this seems to be non-consistant the causes can be the outside of the mic as well as the inside.
Easy check is to shoot out the outside.Just plug the mic to another channel,swap the xlr cable.
After this you'll know a lot more.
When it is the mic itself we must know a little bit more to help you.
What's the gain on your preamp or channel input set to and how exactly do you monitor this?
We need as much as possible info!Sometimes it's not the issue you're looking at (the mic ) but something completely different-maybe just a broken headphone amp or a section on the monitor controller etc.So let's shoot these possibilities out first.Maybe you have never noticed it because any signal will cover these plops.
O.K.,up to here.
Next step is investigating the mic.The plops don't sound like a loose wire,more like a part is charging and discharging randomly.Can be a faulty cap.
A very important question is then in which mode this happens?
If it is in cardioid check the plops again,listen to them and switch the mics hpf in and out.If the sound of the plops change then I bet it's the capsule itself.If not it must be after it in the circuit,I would still think then it is in the high impedance part.

So first make clear all surrounding stuff and the listening situation.

Let us know,good luck,

Udo.

 

[kante1603]

@Hellfire

Hi,

haven't seen the other thread,sorry for that.
I didn't write he has a workaround but a possible one. He's asking you to tell him what preamp you are using,I bet he wants to know the load impedance of it.Might work,give it a try.

Cheers and sorry for overseeing,

Udo.

 

[kante1603]

When I switch the hpf the sound is still there too just a little less bass, hahhahahah.  And the -10db switch helps but I can still faintly hear it in there.

Its seem that when the mic is cold it doesn't do it until it warms up.  I will have to check that later though. once its cold again.

Thanks for all your help.
-Scott

O.K. Scott,we're getting closer!
Yes,it is the mic that is faulty,not the listening condition,hahahahaha.......
Since the hpf affects the sound we can clearly say that it is coming from the source before(!) the filter,right?And that's the capsule.Please look at the schemo,there are not many parts around it.
Best to check first if this issue is really temperature sensitive.
And you can do another check to get closer to it:
Given that this happens in cardioid mode (you haven't answered that) you can exclude a possible capsule fault from the surrounding parts.Lift the front capsule wires temporarily and swap them to the back capsule.Stay in cardioid mode while testing.Remember you have two nearly identical capsules working there which are even completely isolated from each other.
See if the plops change or even go away,you must check sounds from the back side then.
Have you touched the capsule while mounting,unpacking or screwing to the saddle?

Best,

Udo.

 

[saxmonster]

Udo,
Yes the mic is in cardioid.  Its the only pattern on this mic as it is the Aurycle 460 and i don't have switches for it right now.  Now i just started it up again today and this noise wasn't there but as it warmed up and I did some testing 123 through it it came back.  It almost sounds like when you sit in a leather sofa you get that rubbing / popping sound but it is really faint and below the actually headroom of the mic if that makes sense.  I will try the capsule reverse thing later tonight or tomorrow as I have to go to a gig soon.  If both capsules show the noise then it has to be a competent inside on the pcb right?  I was very careful not to touch the capsule at all when installing it.  I just touched the sides where the screws go into to attach it to the mic.

Thanks again
I will post my results when I flip the capsule sides by flipping the wires.

 

[DUDE GUY]

I'm scoping at the drain and I neglected to mention that I have no transformer connected. From what I've read in this thread, I don't need the transformer to bias the FET. Am I mistaken?

Also, I'm injecting the 1k tone at R6 (installed backwards, as suggested by poctop). Correct?

Thanks Magneto.

Hey there, Dude ...

1. The mic will not output the 1k sine tone. I see it on the scope, but cannot
see any signal coming back into my daw (I've checked my signal chain going to my
daw and all is good). Thoughts?

2. I attempted the bias procedure, but the only symmetrical distortion I can
achieve looks like the attached picture and I assume this is bad. My scope is
pretty old, maybe it's the problem?

Where are you scoping that signal? At the drain or coupling cap? If so, that distortion, and the fact that there is no output from the mic, suggest a short at the secondary.

The scope is not the problem.

 

[kante1603]

Udo,
Yes the mic is in cardioid.  Its the only pattern on this mic as it is the Aurycle 460 and i don't have switches for it right now.  Now i just started it up again today and this noise wasn't there but as it warmed up and I did some testing 123 through it it came back.  It almost sounds like when you sit in a leather sofa you get that rubbing / popping sound but it is really faint and below the actually headroom of the mic if that makes sense.  I will try the capsule reverse thing later tonight or tomorrow as I have to go to a gig soon.  If both capsules show the noise then it has to be a competent inside on the pcb right?  I was very careful not to touch the capsule at all when installing it.  I just touched the sides where the screws go into to attach it to the mic.

Thanks again
I will post my results when I flip the capsule sides by flipping the wires.

Cool to hear,yes,you're right:If the same plops are audible with the back capsule attached to the front capsule pcb connection then it is just a component,I would guess a cap then.
Thank you for the reply,have a nice gig,

Udo.

 

[saxmonster]

Would the mic work if I had the capsule totally disconnected this way if I still hear the noise I would know its inside.

 

[wave]

It should right?
I think you have to put in the 51pF caps in place of the capsule diaphragms tho.

Dany, Udo, anyone else feel free to correct me!

Dave

 

[kante1603]

Hi,

looking at the original schemo Neumann specifies both capsule sides having a capacitance of 50pF,so I think yes it should work.
But I'm still interested if it is the same when the front and back capsule flipped  :

Cheers,

Udo.

Edit:just in case the plops stay as they did before,do you have styrenes in your mic?I know that styrenes definetely don't like too much heat,only short soldering.Maybe something like that......

 

[HellfireStudios]

FWIW/FYI, I'm getting a pair of "BV11" transformers from AAMicrophones for the HST-11a mod. His specs are 5:1 also.

That's what I was afraid of...

All may not be lost....what will you be plugging this mike in to?  What kind of preamp?

Sorry, I must have completely missed this post on the first read. The preamp will most likely be a modded GAP Pre73 (1.2k ohm and 300 ohm selectable input impedance/Transformer coupled).  A Trident A-Range Clone may be down the line as well. I apologize again that it took this long to answer.

-James-

 

[kante1603]

@Scott,

Did some search on the aurycle site and hopefully I do now get this right when saying you use the stock capsule?Is that the reason why your mic works in cardioid only?
That would make sense then you asking for dropping in a cap instead.
Little confused now(have built DOAs the whole night long and am tired at the moment),

Udo.

 

[wave]

So I have a few transistors and I don't have a rig like Udo's for testing nor do I have the parts to make one. My question is,
what kind of test can I do with my DMM (true RMS Fluke) to pick the best transistor? The meter does not have a transistor socket

Thanks,
Dave

 

[poctop]

So I have a few transistors and I don't have a rig like Udo's for testing nor do I have the parts to make one. My question is,
what kind of test can I do with my DMM (true RMS Fluke) to pick the best transistor? The meter does not have a transistor socket

Thanks,
Dave

Lowest Idss you can find ,

here is the method
How To measure FET Idss By Matador :https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819937f0

 

[wave]

Another question:
Does the low cut engage when the pin connections are shorted? The Aurycle comes wired with the switch being closed in the low cut off position. So if the low cut engages on the mic when the pins are shorted the wire on the Aurycle switch needs to be rewired.

Dave

 

[kante1603]

Another question:
Does the low cut engage when the pin connections are shorted? The Aurycle comes wired with the switch being closed in the low cut off position. So if the low cut engages on the mic when the pins are shorted the wire on the Aurycle switch needs to be rewired.

Dave

Hi Dave,

Yes,you're right.Somebody else here had the same issue.Please see my reply #153.

Cheers,

Udo.

 

[wave]

Thanks Udo!
I know I should have gone back and re read the thread but I'm at the point where I just want to be finished with this one.

Here's another which has probably been answered.
Can I solder the 2 50pF caps right to the FC and RC headers the proceed to biasing and testing before I put the actual capsule in?

I know I'm being lazy please feel free to flame me at your leisure

Dave

 

[kante1603]

Thanks Udo!
I know I should have gone back and re read the thread but I'm at the point where I just want to be finished with this one.

Here's another which has probably been answered.
Can I solder the 2 50pF caps right to the FC and RC headers the proceed to biasing and testing before I put the actual capsule in?

I know I'm being lazy please feel free to flame me at your leisure

Dave

Had to look for what your last sentence meant,still learning english,hahaha....
For biasing:No,you leave the capsule pads open,don't solder the caps in.These are meant for replacing the capsule(s) when you are tracking errors and do not want to damage them.
Biasing is done without capsule.

Best,

Udo.

 

[wave]

Thanks Udo!
I'm trying to assemble some clear concise instructions for the 1K tone listening bias method.

Dave

 

[DUDE GUY]

Hello All,

I'm having some issues here. I'm not able to see the 1k tone coming out of the mic into my DAW. I can see the 1k at the FET drain and I've checked my signal chain coming out of the mic into my DAW and all is in order. Additionally, my FET bias resulted in symmetrical distortion, but there is clearly something wrong (see attached pic).

Info:

-My scope is connected at the FET drain.
-I have no transformer connected (waiting for a T13)
-I'm injecting the 1k tone at R6 (installed backwards)
-I have no capsule connected and I do not have anything in place of the capsule (i.e. 51 pF caps)

Source V: 48.0V
L1 & L2: 46.6V
Zener: 22.88V
R18: 46.6V
R19: 46.1V
Top of R17: 22.89V
FET Drain: 10.53V
FET Source: 2.62V
R12: 10.54V
R13: 43.4V
R14: 20.73V
R8: 39.7V

According to MagnetoSound, I may have a problem with my secondary. As a total noob, I'm not exactly sure what the secondary is (a second gain stage?) nor do have any idea where to start troubleshooting.

Any help with this would be much appreciated. Thanks very much everyone!!!

-DUDE GUY

 

[wave]

Can anyone tell me which wires are which on the AMI T-13?

Dave

EDIT: Found it in one of Adeptusmajor's posts