Neumann Vintage U87 Clone : Build Thread.

[wave]

So I messaged Matador and he said we should debug this in the thread.

I'm having an issue where my mic (the first one) powers up and sounds great but I have random complete volume dropouts.
The volume will totally drop and then kind of ramp back up to full. Then it will randomly happen again.
Do you guys think this is an issue with one of my caps (I'm using styrenes and they are a bit touch sometimes )?

Dave

 

[saxmonster]

I had an issue with C3 being noisy and static pops. I used the other option and it went away so I had to order a new styrene.  Could it be the phantom power dropping out or something?

 

[wave]

You should strongly consider purchasing on of Eric's (tskguy) capsules. They are great. The Rk-87 is a great capsule for the money but you def need to go with the T-13 and all vintage caps with that capsule. I used that combo in my first mic and there are some samples I posted of it earlier in the thread.

I have been asked by a few other people to build mics for them and I'm pushing Eric's capsules to them as well.

Dave

Hi Dave,

Based on your story at GC and my personal preference for Funkenwork iron, I had planned on using the RK-87 capsule with styrene caps.  Is your recommendation for tskguy's capsules based on (aside from their apparent high quality) their capability with the Cinemags and modern components?  Do you plan on trying Eric's capsule in the T-13/styrene circuit to see how the capsules sound comparatively?

Thanks!

Hi Corusco,
I know that if you go with the RK-87, T-13, and styrenes you will have a great sounding mic. If you put one of Erics capsules in with those same components you will have a great sounding mic with creamy mids and super silky top end.
If you can afford it, do it for sure.

I have a 2480 here already but I think my long term plans are to use Eric's capsules with either iron.
I do plan on dropping one in my AMI/styrene mic soon.

Welcome to the forum by the way!

Dave

 

[sr1200]

Yeah i have an issue where the mic cuts out but if you switch the pad on/off it comes back for a sec or 2 then just fizzles out.

 

[wave]

SR1200,
Are you using styrenes in your build too?

Dave

 

[poctop]

So I messaged Matador and he said we should debug this in the thread.

I'm having an issue where my mic (the first one) powers up and sounds great but I have random complete volume dropouts.
The volume will totally drop and then kind of ramp back up to full. Then it will randomly happen again.
Do you guys think this is an issue with one of my caps (I'm using styrenes and they are a bit touch sometimes )?

Dave

sounds to me as a bad contact anything arround the Fet or supply to it or R11,

have a double check just to make sure ,

Hope this helps,

D

 

[DUDE GUY]

Work in progress Sneek Peek , 

D

YESSSSS, I'LL BUY 2!!!!

 

[kante1603]

Hi brother Dan,

Maybe it's a good idea to open a new thread before topics get messed up here?
Just a thought.......

Udo.

 

[sr1200]

The one thats working fine is styrenes, the non working one no styrenes.  It looks to me i might have some bad caps at the top, i gotta replace them and see if that does it. they may have cooked too long with the iron.

 

[Matador]

For those using styrenes:  those are notoriously hard to solder.  You really have to hit the joint with the iron and get it soldered within a few seconds.  One tip that helps is to add a thermal mass to the joint:  such as an alligator clip that has no wires.  You can clip it to the lead coming out of the board on the component side, then solder on the underside of the board.  The idea is that the lead will absorb some heat before it gets to the cap to minimize the change of damage.

Caps that go to ground with a ground plane are especially hard as you have to heat the plane as well which takes even more time and is prone to cold solder joints.

 

[poctop]

Hi brother Dan,

Maybe it's a good idea to open a new thread before topics get messed up here?
Just a thought.......

Udo.

you are correct Sorry for the confusion ,  i am not at the thread stage yet tough  :-X

 

[poctop]

For those using styrenes:  those are notoriously hard to solder.  You really have to hit the joint with the iron and get it soldered within a few seconds.  One tip that helps is to add a thermal mass to the joint:  such as an alligator clip that has no wires.  You can clip it to the lead coming out of the board on the component side, then solder on the underside of the board.  The idea is that the lead will absorb some heat before it gets to the cap to minimize the change of damage.

Caps that go to ground with a ground plane are especially hard as you have to heat the plane as well which takes even more time and is prone to cold solder joints.

This is a great wisdom and experience comment from Matador. have a look to the Capacitor that are in the ground plane connection,

Dany,

 

[kante1603]

+1 on this matador,thanks for pointing us to it!
Styrenes are easy to kill,sometimes it helps to solder multiple parts on just one leg each and then move to the next part.I do this any time when soldering switches built in weak plastic housings or multipin parts like transistors,ICs etc.When soldering alternating the previous soldered parts have more time for cooling down.
The alligator clip is really "cool"
Udo.

 

[kante1603]

you are correct Sorry for the confusion ,  i am not at the thread stage yet tough  :-X

No confusion yet,it was meant as a preventive post...

Cheers,

Udo.

 

[HellfireStudios]

Don't know why this crossed my mind, but I remember someone earlier in this thread mentioning using a small value cap (1.5-2.2pF) across the FET to bring it to proper THD and frequency response spec.
Here is the post I saved for future reference.

"Hi Dan,
Did you measured amp specs via test input? There is Neumann U87i specification at page 8:
 http://www.neumann.com/download.php?download=copi0042.PDF
I had a problem to meet frequency response specs, as well as THD specs. 
After some research I found simple way to tune the circuit to original specs by adding 1.5-2.2pF capacitor between Gate and Drain of FET. Why so? I think that modern 2N3819 FETs have much lower reverse capacitance than original ones from 70s.
Hope it can help in U87 black magic."

The reason I posted this? Is it possible that the gain of the 2N3819 could be adversly by this lack of reverse capacitance. I honestly don't have enough electrical knowledge to even guess, but it doesn't hurt to ask. I hope we can resolve the lower-than-it-should-be gain problem soon. I'm itching to build.

 

[poctop]

Don't know why this crossed my mind, but I remember someone earlier in this thread mentioning using a small value cap (1.5-2.2pF) across the FET to bring it to proper THD and frequency response spec.
Here is the post I saved for future reference.

"Hi Dan,
Did you measured amp specs via test input? There is Neumann U87i specification at page 8:
http://www.neumann.com/download.php?download=copi0042.PDF
I had a problem to meet frequency response specs, as well as THD specs.
After some research I found simple way to tune the circuit to original specs by adding 1.5-2.2pF capacitor between Gate and Drain of FET. Why so? I think that modern 2N3819 FETs have much lower reverse capacitance than original ones from 70s.
Hope it can help in U87 black magic."

The reason I posted this? Is it possible that the gain of the 2N3819 could be adversly by this lack of reverse capacitance. I honestly don't have enough electrical knowledge to even guess, but it doesn't hurt to ask. I hope we can resolve the lower-than-it-should-be gain problem soon. I'm itching to build.

The gain will be lower that the AI version this is a fact of the circuit,  i did order a replcement FET for my vintage neumann a while ago strating the project and the 2N3819 was the FET i received straight from berlin with the matching R11 at 8.26K so there is no doubt it is doing the Job

i did compare the U87 vintage to the u1621  here and the gain is virtually the same,  using the T13 will be at 9.5:1 and cinemag at 10:1.  Hence i have no problem with the gain as i record with both with great sucess,  just my 2 cents,

Dan,

 

[Matador]

Don't know why this crossed my mind, but I remember someone earlier in this thread mentioning using a small value cap (1.5-2.2pF) across the FET to bring it to proper THD and frequency response spec.
Here is the post I saved for future reference.

"Hi Dan,
Did you measured amp specs via test input? There is Neumann U87i specification at page 8:
http://www.neumann.com/download.php?download=copi0042.PDF
I had a problem to meet frequency response specs, as well as THD specs.
After some research I found simple way to tune the circuit to original specs by adding 1.5-2.2pF capacitor between Gate and Drain of FET. Why so? I think that modern 2N3819 FETs have much lower reverse capacitance than original ones from 70s.
Hope it can help in U87 black magic."

The reason I posted this? Is it possible that the gain of the 2N3819 could be adversly by this lack of reverse capacitance. I honestly don't have enough electrical knowledge to even guess, but it doesn't hurt to ask. I hope we can resolve the lower-than-it-should-be gain problem soon. I'm itching to build.

This is a way to add a touch of local negative feedback which reduces gain at high frequencies.   It's possible the new FET has higher bandwidth and this is a way to tame that bandwidth down.

 

[HellfireStudios]

The gain will be lower that the AI version this is a fact of the circuit,  i did order a replcement FET for my vintage neumann a while ago strating the project and the 2N3819 was the FET i received straight from berlin with the matching R11 at 8.26K so there is no doubt it is doing the Job

i did compare the U87 vintage to the u1621  here and the gain is virtually the same,  using the T13 will be at 9.5:1 and cinemag at 10:1.  Hence i have no problem with the gain as i record with both with great sucess,  just my 2 cents,

Dan,

Good to know that it seems to be the same gain as the vintage it clones, but I believe Udo feels his is about 6dB quieter than it should be. I believe he feels it is about 16dB quieter than the U-87Ai he has for comparison. It should be 10-11dB, right? This is why I asked.

Thanks for the explanation, Matador. It might help, if anything seems harsher than I feel it should be.

-James-

 

[kante1603]

Good to know that it seems to be the same gain as the vintage it clones, but I believe Udo feels his is about 6dB quieter than it should be. I believe he feels it is about 16dB quieter than the U-87Ai he has for comparison. It should be 10-11dB, right? This is why I asked.

-James-

Hi James (and all you brothers of the solder fume of course),
I did some further searches.Dave (member "wave") was so kind to share his results comparing his clone to an AKG C414 B-TL II.
He wrote they´re about 11 to 12 dB off from another.O.K.,so far so good.
But when you look at the specs there must be something wrong,too far off at least:

Again:
A U87 vintage version seems to not have changed in  output level between 1972 and 1980,the specs say 0,8mV/microbar.This is the same as 8mV/Pa.This equals -41,9xxx dB (dB re 1V).
Next we have the U87Ai (btw,the "i" only means "international type and refers to the xlr connector,just for info....).This is specified at 28mV/Pa which equals -31,05xxxx dB (dB re 1V).
O.K.,we all know that this is much hotter.

Funny thing:An AKG C414B-TL II is (or was,it´s discontinued...) specified at 12,5mV/Pa which means -38dB (dB re 1V)-and that is-compared to our clones-around 3dB off (C414 hotter of course),but not 11 to 12 dB!

Maybe I don´t get this right?Or is it only my clone thinking of that it seems I had the lowest idss of all?But why is Dave´s clone off too?Questions,questions,questions............. :

For your thoughts,good night,

Udo.

ADDENDUM:I looked at the original schematics some minutes ago-the voltages at the capsule pads should be 47vdc-I remember most of us had around 40 or 41vdc at the pad-is that a hint,have we overseen something at this point?

 

[poctop]

ADDENDUM:I looked at the original schematics some minutes ago-the voltages at the capsule pads should be 47vdc-I remember most of us had around 40 or 41vdc at the pad-is that a hint,have we overseen something at this point?

I did measure on my vintage with my fluke here and it does read the same as the clone 40V,  however if somemone would be able to confirm that back with another vintage then that would be extra ,  the HZ bias measurement on the meter is the same for both tough , so i might be 47V but they read the same hopfully,  are you  Brther Dave and  Udo  running on the same capsule ?, for sure the cinemag should affect the output a tiny bit more than the T13 but still be very comparable.

that would be very interesting on establishing sort of a reference at somepoint, 

anybody with a vintage that could corroborate these data ,


Dan,