Neumann U 47 Clone - A DIY Bachelor Thesis

[Zottel]

Hey! 

Working on the mic and wondering if anybody has a clue about the pins of the vf 14. I found 2 pictures that show a diffrent numbering. 

This one:

The sheet from the ef14. The vf14 sheet says the pins are identical to the ones of the ef14.
The pins are written down in the second column under "stift"

Edit: I think i helped myself  :
This schematic shows it:

 

[Zottel]

So this is what the mic looks like after todays session.

Next week im hitting the road straight to Mr. Grosser.
Lets hope for the best!  ;D  ???

 

[Zottel]

Just to make sure ive got it right:  :

In the lower left corner is a pinout of the VF14. It says " auf den Röhrenfuß gesehen".
"Röhrenfuß" stands for the socket of the tube. And this socket is shown from the tubes view. So we see the holes where the pins of the tube go in. This basically means that the soldering points at the backside of the socket relating to the pinout of the schematic, are mirror inverted. Did i get this right?  ???

 

[ln76d]

Pinout should be shown at backside of the socket - it's common standard in tubes datasheets.

 

[leadbreath]

love this thread...

 

[Pip]

Yes all tube layouts are from the direction of the bottom view. The socket wiring view.

 

[AusTex64]

So this is what the mic looks like after todays session.

Next week im hitting the road straight to Mr. Grosser.
Lets hope for the best!  ;D  ???

Very impressive build!

 

[Zottel]

Thanks for your help guys! 
It’s so cool to have your input! This mic is my first build that’s why I want to be 100 percent sure about the things I do. Before this build I only did some small guitar effect pedals (like boosters and such) and these kits where ultra-cheap and easy!
The U47 build is in a whole different world. So sorry if I’m bombarding you with dumb questions about things I should already know.
@AusTex64:  thanks! I really appreciate it! 

 

[Pip]

So this is what the mic looks like after todays session.

Next week im hitting the road straight to Mr. Grosser.
Lets hope for the best!  ;D  ???

So impressive build! I have one suggestion. I think you should replace the drop down resistor from a cast sand to an chassis mount aluminum heat sink type of at least 10 watts rating if possible. Are you using a 1780 OHM or a 1500 OHM? If you are using 1.5K its easy 1.78K is out there I have some but they are MIL Spec and expensive.

 

[0dbfs]

Where do you get those 1.78k mil spec ones?

Thx!
Jonathan

 

[Pip]

Where do you get those 1.78k mil spec ones?

Thx!
Jonathan

You have to search the web constantly and they will pop up in short supply the last bunch I found I bought all of them.

 

[Zottel]

Hey!

Wanted to let you guys know that the mic is up and running! Mr. Grosser was kinda "astounded" because he wouldnt have expacted such a good first build. Very low noise, and no crackle.

So thanks again for all your help!

I was searching for the 1,78k one. Could only dig up some 1,8k ones. So i guess i will stick with my "crazy horse" for know. lets see how hot it will get.

 

[Zottel]

Today is a sad day After I got home from Andreas i didnt touch the U47 for a while. Today i tried to test the microphone for the first time at my home but sadly there is nerly no output! (It was working very well in Berlin!) Only if im screaming very loud in the near of the capusle there is a tiny tiny tiny little bit of output.

I stared to check if theres something broken inside, but everything looks fine.
I was measuring the voltage from ground to counter electrode of the membran. The Voltmeter shows 5,6 Volt. (In the schematic it shows 60 Volt) And when I'm measuring before the 100 M Ohm resistor infront of the counter electrode it shows 56 Volts. Could it be possible that the capusle is underpowered?

 

[useme2305]

you cannot measure the voltage in the super hi-z area around the capsule with your voltmeter. also 56V before the 100Mohm sounds OK, right everyone?

it's something else. check if there's is an area connected with GRND that's not supposed to be. that's always the first thing i do.

did you do your tests with andreas with the body tube off? maybe it's touching something?

 

[ln76d]

Today is a sad day After I got home from Andreas i didnt touch the U47 for a while. Today i tried to test the microphone for the first time at my home but sadly there is nerly no output! (It was working very well in Berlin!) Only if im screaming very loud in the near of the capusle there is a tiny tiny tiny little bit of output.

I stared to check if theres something broken inside, but everything looks fine.
I was measuring the voltage from ground to counter electrode of the membran. The Voltmeter shows 5,6 Volt. (In the schematic it shows 60 Volt) And when I'm measuring before the 100 M Ohm resistor infront of the counter electrode it shows 56 Volts. Could it be possible that the capusle is underpowered?

Check plate voltage at the tube, check heater voltage before and after 1.8k resistor.
Check that resistor!
Check all the ground connections.

you cannot measure the voltage in the super hi-z area around the capsule with your voltmeter. also 56V before the 100Mohm sounds OK, right everyone?

Right!

 

[Zottel]

We tested the mic with the body.
Tested all the ground connections and checked if something is connectiong to ground that shouldnt. Nothing. :/
I also checked the connectors and the mic cable.

Plate voltage from tube to ground says -106,7 Volt
The resistor says 1780 Ohm but the heater voltage seems to be 108 Volt (measured from the heater pin to ground)?
0 volt when i place the voltmeterpins before and after the 1780 Ohm resistor.
I tried a diffrent resistor. Same situation.

 

[useme2305]

did you carefully check the cable? do a thorough continuity check from end to end of each pin and check each pins against every other one for accidential connections. are hair sized strand from one of the lugs on the connectors solder side could be the culprit. do the same checks inside the psu. it's strange that it worked at andreas' place and didn't at your's after trasporting it which leads me to believe that it might be a issue with a bad connection.

also do a continuity check between backplate and front/rear diaphragm a trace of body oil or condensation water can cause massive problems but they would normally include noise and not just a low signal.

 

[useme2305]

also, while looking at the pic of the open mic i noticed that the screws that hold the tube socket etc inside the rails are very long almost touching the  socket lug and the little vero board on the tranny....looks weird. i'd avoid that. dremel them shorter or find shorter ones.

 

[Zottel]

Thanks for all your help! I checked all of the stuff. I even soldered the connectors again. With ptfe tape around every socket. Still didnt work.

My last Idea was to try to measure the heater resistance of the tube. Its infinite. So i guess this might be the problem. 

 

[Matt Nolan]

My last Idea was to try to measure the heater resistance of the tube. Its infinite. So i guess this might be the problem. 

I'd say so. And here's your clue to it having gone open circuit:

the heater voltage seems to be 108 Volt