Neumann Vintage U87 Clone : Build Thread.

[Deepdark]

Is that make a difference if I cut pin A (1) instead of pin C (3) as recommanded? If yes, why (personal knowledge)

 

[Deepdark]

Nobody? Thanks giving has been hard for you folks  ;D

 

[poctop]

Nobody? Thanks giving has been hard for you folks  ;D

Yes sure .

if you have to cut pin ,  i suggest you install the pot the other way arround the adjusment screw facing not the FET but the transformer it will be easier for you ,.

if you have a close look to the board , there are only 2 traces that are connected to the pot , 1 is a ground and the second one lead to the FET drain,

just make sure you use those 2 pins

Hope this helps,

Best,
dAn,

 

[Deepdark]

Yes I use those. Pin 2 is the ground and the other one goes to the fet. So cuting pin 1 or 3 on the pot doesn't change anything, the result will be the same as long as I keep 1 or 3 and pin 2?

 

[fsalter]

Hi folks

I believe it was Mickeyfree who had a dilemna concerning which traces to cut on his B2 switch PCB. That enlightened me to the possibility that i may have a problem too. I use an MXL 2010 donor body for my second U87.( my first was a microphone-parts limited edition body...quite simpler to connect) According to the pics i'm attaching, do you know if there is any trace i should cut to avoid a short on its switch PCB? I removed all components.
Thanks

 

[kante1603]

@fsalter

Yes,I'd cut the trace on the pattern switch that goes to ground,so the lowest of the pin "trio".
Filter and pad seem o.k.,you can leave the middle pin connected to it's neighbour pin and attach one wire there.The leftover single pin connects to the second wire then.Works for both,switch active will be with the knob/lever(?) to the outward position (on both).

Best,

Udo.

 

[fsalter]

Thanks Udo

So just to be sure. Would this be alright ?

 

[poctop]

Yes I use those. Pin 2 is the ground and the other one goes to the fet. So cuting pin 1 or 3 on the pot doesn't change anything, the result will be the same as long as I keep 1 or 3 and pin 2?

i dont have the pcb with me but if i recall correctly only one pin on the 3 pins goes to ground and 1 pin out of three goes to the fet drain ,

then it does matter where you cut the pin ,  just make sure you solder the middle pin of the pot and then use the other one that leads to ground because it will not work .

Best,
Dan,

 

[kante1603]

Thanks Udo

So just to be sure. Would this be alright ?

Bull's eye!

;D

 

[Deepdark]

here is an update of my situation. I change the fet, so now I succesfuly calibrate it at 11,5V. Now my new troube, I just have 17V at FBK (supposed to be 40V). Could it be the trany that causes that? Maybe the secondary? Which voltage do I supposed to get on the secondary? I get 0V.

 

[Deepdark]

by the way, I got +/- 30V at AA. All other voltages looks great exept CC/FBK and RBK, where I get 0,03V. It's really weird. I really don't see where is the error. All switches are disconnected, the capsule not installed.

 

[Deepdark]

and another issue, when I touch certain places with my fingers or the dmm, like R14, R8, RBK, the meter on my daw clip in the red. Is that mean that there is a short somewhere?

 

[Deepdark]

Anyone?

 

[kante1603]

Anyone?

Will you please stop putting people under pressure?
This is diy,patience is the key.
The members here are spread around the entire world,and there is a serious time delay between  some countries........hell,some of us even have a daily job.
This is not a 24/7 full service.
Four posts within 59 minutes is more than enough.
Touching parts wildly/randomly with your fingers in a high impedance area is a really bad idea btw..
What does +/- 30 v mean....etc.
I'm now afraid what will happen when you try to mount and connect the capsule.........

Udo.

 

[Deepdark]

I'm so sorry. It wasn't my intention to put someone into stress. My apologize guys. I know you're doing your best and it's really amazing what you do. Thanks for that and again, sorry. :-[ 

To answer you Udo, I've attached the schematic of the first board, with annotations. I put the voltages I got, and draw in yellow the portion of the circuit that I'm sure is ok and in green, where I suspect it could be the culprit. I don't know which voltages I'm supposed to get in the green section so if someone could take a look. Thanks in advance 

 

[Matador]

You can't measure the polarization voltage with a regular DVM.  The bias current it draws to do the measurement will drop across all of those filtering resistances and mess up the results.  You need a special high-impedance buffer to do the measurement.

If you've verified the 45V-ish voltage after the 2.21k phantom tap resistors then the polarization is probably fine.  Does the mike work?  What is the problem you are experiencing now?

 

[Deepdark]

Hi. Thanks matador. Yeah the L1 and L2 voltages are ok. So polarization is good. The only problem I get is that I'm supposed to get 40V at C5/FBK/RBK but at C5/FBK I only get 17V and RBK +/- 0.06V or so. The capsule and switch aren't installed yet. I calibrate drain of the fet to 11.5V,  so what I think is maybe the problem should be around R13/15/16. That part of the circuit which inject voltages C6/R8/AA. I got 29V there. Maybe it's where the problem resid?

 

[mica]

Im trying to do the FET adjustment, and thought i understod it from reading these pages. (My first mic build)

The capsule is disconnected.

First i connected to R6 which i installed backwards as described (green wire) which i soldered to the center of the minijack. I attached the white wire to the ground og the minijackconnector at put the other end on the mic body:

Second i connected my mulimeter to first leg on the fet (from the edge og pcb) and to the drain connected to GG. Set the meter to V.

Then i opend logic and sent a 1ghz sine wave tone to output at 0DB:

I get a reading of aprox. 1.2 V. and adjusting R11 doesn't make a difference..

What am i missing?

 

[HellfireStudios]

Your transformer primaries should be disconnected as well.

-James-

 

[poctop]

Im trying to do the FET adjustment, and thought i understod it from reading these pages. (My first mic build)

The capsule is disconnected.

First i connected to R6 which i installed backwards as described (green wire) which i soldered to the center of the minijack. I attached the white wire to the ground og the minijackconnector at put the other end on the mic body:

Second i connected my mulimeter to first leg on the fet (from the edge og pcb) and to the drain connected to GG. Set the meter to V.

Then i opend logic and sent a 1ghz sine wave tone to output at 0DB:

I get a reading of aprox. 1.2 V. and adjusting R11 doesn't make a difference..

What am i missing?

you are probably confusing adjusting the voltage with a sine tone ,  the sine tone is for biasing with a scope ,

so lets do a initial adjusment first ,  make sure the capsule is out of circuit or removed,  then set your DMM to dc Volt and stick the red probe on the drain pin of the fet and the black probe to the mic chassis,  and then adjust the pot R11 to read approximately 11.5V DC on the drain pin of the FET, make sure you removed any connection to the middle pin of the fET wich is the gate ,

once you have done this adjusments  try the mic out and see wassup ,  then if you have a scope you can tweak this adjusment by injecting a 1K sine tone trough r6 leg, do not add another probe to the fet gate.  then with the red scope probe on the drain pin of the fet and the black on the mic chassis , set the scope so you can see the sinus output from the scope and then increase the amplitude of the signal until the sine wave flat out,  the idea of this adjusment is to have the sine flat out equally on both phase at the same time so in short both top and bottom should flat out at the same time as you increase the amplitude of the signal . to see that happen you need to cycle the amplitude of the sine tone up and down while tweaking that drain value until this happens and then you have the optimized bias point.

hope this helps,
Best,
dAn,