Neumann Vintage U87 Clone : Build Thread.

[kante1603]

Attention to all completed project  ;D  your are very welcome to post in this thread to let us know how you are making out,  8)

Regards,

Dan,

+1 on this,there seem to be a lot of of builds just half-working or so,I don't see the solutions.We all want a good working microphone,don't we?
And posting some statements about sound,maybe compared to a real U87(Ai) and telling us something about using different caps,trafos and capsules would really be nice of you.

Udo.

 

[poctop]

I Have those 4 Mics perfectly working but i guess that does not count does it ?  ;D

 

[kante1603]

I Have those 4 Mics perfectly working but i guess that does not count does it ?  ;D

No.

Sincerely yours,
"the-guy-who-dances-with-no-microphones-because-he-is-hungry-for-transformers" Udo. ;D

 

[poctop]

Here is a shot with my vintage U87 and  my beloved 2 clone,  with original Traffo and peluso capsule , i need to polish the capsule mount positioning tough because there is i believe some slight proximity effect difference i believe ,  fun game is to try finding the real one in those 3 regardless of the take slight difference and my horrible voice, now it is time for T13 and RK87 to show up and compete,.

have fun, 

there it is ,

clone and neumann against sample,  8)
https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819937b3

Cheers,
Dan.,

 

[wave]

My guess is the real one is #1

Probably wrong tho. The similarity is intense. Do I hear some slight distortion on 2 and 3?

Dave

 

[berkleystudios]

okay when i introduce a 1k signal at -50db, i get a jump at the drain to about 15v, and then it fluctuates all over the place. it is not constant. could it be a grounding issue? will  put pics up later, just got off work so im to tired to do it now.

also i get no voltage at the gate, and the source typically is the same voltage as the drain.


this is the first time ive biased something so im sure im doing it wrong haha.

here is a rundown of what i am doing.
1) connect xlr cable an supply phantom power
2) check zener (shows 24 volts)
3) ground DMM on out side of mic XLR chassis(0.0V)
4) check voltage at drain (7.3v) (no signal applied), highest voltage achieved by adjusting trimmer
5) same voltage a source
6) apply signal to RT using a 1/8" TR adapter  on a 1/4" TR cable, 1khz at -50db
7) voltage fluctuates at drain and source but normalizes to 7. V eventually, adjusting trimmer does not increase.

what am i doing wrong? looks like 2.52k is max resistance

 

[saxmonster]

maybe the pot is trashed or they sent you a wrong one or a cold solder of the pot?

 

[kante1603]

Hi,

O.k.,there's something wrong definetely.
Pics will help of course,best from both the parts and solder side.
I guess you had the capsule disconnected?
At first check for even smallest solder blobs and shorts.
The 2,52k,did that refer to your pot fully dialed in to one side or did I misunderstand something?If this is the "end value" and arround 0ohms on the other side then you might have put in a wrong pot.
It can be the fet is broken or has a connection between source and drain,same voltage on both is wrong I think.
The 24vdc on top of zeners is right,even perfect.
Also you started with -50dB on the measuring input,but that's a different thing.Let's get the mic up and running first.

Best regards ,

Udo.

Edited,let´s check the pot first.

 

[kante1603]

Hi Dan,

the last sample is distorted,sorry....

Udo.

Edit:If you can record a short sentence containing all (the german word is "Vokale") vowels(?,meaning A-E-I-O-U) it might help.An "A" e.g. has the highest energy,a "U" tells something about low mids etc.."Check,check...." is too little to judge a sound.
Anyway,all mics sound good on a first listen,and they don´t have the sharpness all this china stuff has,nice!

 

[kante1603]

My guess is the real one is #1

Do I hear some slight distortion on 2 and 3?

Eeeehhhmmmmm....."slight" distortion on #3?

 

[kante1603]

Just tought i giving some figures regarding the bias of my new pair of U1621, suprisingly or not  ;D the Iddle current sit exactely at the same level for both mic after bias procedure ,   

Mic A  Drain Voltage 10.3V  source Voltage 2.77V    iddle current trough R11 12.2K =  0.226 ma

Mic B  Drain Voltage 10.1V  source voltage 1.86V    iddle current trough R11  8.2K  =  0.226ma ,

results from this JFET below


cheers,
Dan,

Hi Dan,

It's boring to wait for parts,so I did a comparison to your results.
I have 2,568vdc as source voltage and 12,56 k for R11.Idle current therefore is 0,205mAs.
As said idss from my fet was lower,arround 8,7 mAs.
Still in the ballpark I think.
Just for info.

Cheers,

Udo.

 

[poctop]

My guess is the real one is #1

Do I hear some slight distortion on 2 and 3?

Eeeehhhmmmmm....."slight" distortion on #3?

Yep there is definately  a little something going on with number 3 , i have been identifying mike with a color scheme bevcause they are exactely the samething,  i am now suspecting the 10pf styrene i obtained from a garbage can, i realy need to polish my capsule placement as well i am not totally happy the way it is mounted inside the mic ,  also the mic will make some room for the RK87 from matt to test out,
still workin on it for sure, 

 

[kante1603]

Dan,does that mean the others have micas for the 10pf and the "normal" styrenes stated as original in the bom?
Just curious,

Udo.

 

[wave]

My guess is the real one is #1

Do I hear some slight distortion on 2 and 3?

Eeeehhhmmmmm....."slight" distortion on #3?

Haha! Makes me laugh every time I read it. I like the throat clearing sound in text form.

Dan- Maybe the garbage can cap has something to do with it? Funny as well!
+1 for Udo's question about whether the others are mica

Dave

 

[kante1603]

Yes,I have read this eeeeehhhmmmmmmm in one of Igor's replies,made me laugh too ;D

Cheers,

Udo.

 

[poctop]

okay when i introduce a 1k signal at -50db, i get a jump at the drain to about 15v, and then it fluctuates all over the place. it is not constant. could it be a grounding issue? will  put pics up later, just got off work so im to tired to do it now.

also i get no voltage at the gate, and the source typically is the same voltage as the drain.


this is the first time ive biased something so im sure im doing it wrong haha.

here is a rundown of what i am doing.
1) connect xlr cable an supply phantom power
2) check zener (shows 24 volts)
3) ground DMM on out side of mic XLR chassis(0.0V)
4) check voltage at drain (7.3v) (no signal applied), highest voltage achieved by adjusting trimmer
5) same voltage a source
6) apply signal to RT using a 1/8" TR adapter  on a 1/4" TR cable, 1khz at -50db
7) voltage fluctuates at drain and source but normalizes to 7. V eventually, adjusting trimmer does not increase.

what am i doing wrong? looks like 2.52k is max resistance

I have updated a lot of info for the project i would like you to verify you initial voltage check in the Read this First and also make sure your gate is actually connected to the other board circuitry and make sure you measure the FET Drain Voltage not the Source Voltage,  you may want to Not solder the potentiometer on the board for now mount it externally so you wont start damaging the pads meanwhile troubleshooting.
make sure also the XLR pinout is respected as a start refer to silk screen.

here is some info that you can find on the First page,  just added them.  hope this will helps finding why you have this problem.

 

[poctop]

And Surely this,

Read This First : Assembly Instruction , Excel BOM and Tips For Assembly and  Imporant Considerations Here: https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819937d0

 

[poctop]

Dan,does that mean the others have micas for the 10pf and the "normal" styrenes stated as original in the bom?
Just curious,

Udo.

Yep they were all poly,  i am suspecting this old cap for sure but also the FET cause when i initially looked at it with the THD meter behavior it seemed to had a less nice THD profile just after the Bias point ,  I Will try another one for now with lower IDss and see. .

 

[kante1603]

Thanks for the great guide Dan,this will help a lot,especially the guys who are not-so-experienced.
Running the 4 connection wires on the bottom sides is a great idea,this will keep the top side cleaner.
May I suggest to add something to your considerations list?
That is to tell people to never touch the capsule or parts of it directly with the fingers.This is the very high impedance part and is absolutely non-forgiving.Wearing thin gloves does the trick.

Best,

Udo.

 

[poctop]

okay when i introduce a 1k signal at -50db, i get a jump at the drain to about 15v, and then it fluctuates all over the place. it is not constant. could it be a grounding issue? will  put pics up later, just got off work so im to tired to do it now.

also i get no voltage at the gate, and the source typically is the same voltage as the drain.


this is the first time ive biased something so im sure im doing it wrong haha.

here is a rundown of what i am doing.
1) connect xlr cable an supply phantom power
2) check zener (shows 24 volts)
3) ground DMM on out side of mic XLR chassis(0.0V)
4) check voltage at drain (7.3v) (no signal applied), highest voltage achieved by adjusting trimmer
5) same voltage a source
6) apply signal to RT using a 1/8" TR adapter  on a 1/4" TR cable, 1khz at -50db
7) voltage fluctuates at drain and source but normalizes to 7. V eventually, adjusting trimmer does not increase.

what am i doing wrong? looks like 2.52k is max resistance

Make sure you inject at C4-R6 point your 1K tone also , make sure your gate is connected and also the capsule is disconnected, make sure you have used pin 1 and pin 2 of the potentimeter and cut pin 3,
Do not use the RT Pad for this method  check here , Put your Probe or Measure the Voltage on the Drain Pin of the FET

Precious Info on how to use a scope to Bias a Fet (Thanks To Matador) http://www.groupdiy.com/index.php?topic=46109.40
also here a reference :
https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819937e2 By ZapnSpark