Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread

[Spencerleehorton]

My first test nickel plate version!!
Getting there.

 

[duantro]

Looking good Spence! Only thing I would suggest for subtle improvements would be maybe polish some of the machining grooves, or bead blast a matte finish out of the body, and get pan head screws to not snag on anything and look cleaner. Like this photo:

 

[Spencerleehorton]

yeah, i'll try and countersink the bottom ones a bit, top ones are ok.
This test piece didn't come out as well as the other two i've done so far, cleaning the attachment wire each time before plating I have started to do and its much improved.
Will post more photos later, trying to crack through them all and running out of time!!!!

 

[Spencerleehorton]

Ok here’s the first two I’ve finished.

 

[Spencerleehorton]

Internal pic

 

[Spencerleehorton]

I’ll do a pic of the round connector as well!!

 

[duantro]

Ok here’s the first two I’ve finished.

Looks great!

 

[BladeSG]

Anyone use the Beesneez U67-U87 body for this project?

If so, could you please let me know the length (inside) of the body so I can work out if it will fit the PCB and transformer?

Also, is the Beesneez BV11 transformer going to work with the 47 FET as it looks as though the spec is the same as the AMI T49?

Any help greatly appreciated.

 

[Spencerleehorton]

Beezneez bv11 should work fine, it’s 10:1 so it’ll work!!
I’ve not had any experience with them though, maybe someone else could chime in?

 

[BladeSG]

Beezneez bv11 should work fine, it’s 10:1 so it’ll work!!
I’ve not had any experience with them though, maybe someone else could chime in?

Thank you.

 

[duantro]

I’ll do a pic of the round connector as well!!

I like the xlr mount, but it is the wrong gender. Should be a male pin connecter, no?

 

[Spencerleehorton]

Your right! Wrong pic, will update with an actual picture of the bottom of the mic don’t worry!!!

 

[JMPGuitars]

Here's a tip for anybody building this:

It's preferred for solder joints to have a mechanical connection in addition to the solder. If you insert the isolation pin backwards, you can create "j hooks" to wrap the pin and have a more reliable connection.

Thanks,
Josh

 

[TillM]

Good idea, but you burned down your styroflex capacitor with the solder shaft.

 

[Spencerleehorton]

These are my first two, finished polishing as best as i can, will be upgrading tools etc so everything will improve and have learnt a lot.

 

[Spencerleehorton]

inside struts and capsule plate.

 

[Spencerleehorton]

3 Pin XLR Connector

 

[JMPGuitars]

Good idea, but you burned down your styroflex capacitor with the solder shaft.

That's exactly as the styroflex was received. It's not burnt, but the "clarity" setting I raised probably made it look a little goofy. There's no burn mark or anything like that on it.

 

[JMPGuitars]

Here's my completed mic. Works perfectly and sounds great with a Beesneez K7 capsule.

Thanks,
Josh

 

[duantro]

I've got one of these assembled and it wasn't working. . I went through and took measurements to compare to Muffy1975's post back on page12 or 13, and Was getting pretty much exactly the same voltages as he was (his didn't work either). I realized that I had a short at pad AA to the screw that I tried to mount to the railing. I pulled that  screw and bracket and after measuring for polarization, I’m getting 15.65v  at AA, and the output is really quiet. Both of my 10M resistors still measure as good. I’ll try to go through and measure all of the transistors again, but not sure where else to look for the low polarization voltage.  I'm using an eab Telefunken 10:1 transformer, and have the higher resistance leads measured going to pad 1 and 2, and the lower resistance measured leads to the xlr pads 3.4. Here are the voltage measurements that Muffy1975 posted a while back:
New measurements

on the 2n3819 T1 i have
drain=  38.8v
source =  23.6v 

on T2 i have 
E= 23.62
B= 22.5
C = 0.592

on T3 i have 
E=38.8v
B=29.57v
C=40.3

T4 i have 
E= 19.7v
b=20.6 v
c= 22.5v

T5 i have 
E=41.1v
B=40.1v
C=20.6v

on T6 i have 
E=0v
B=0.591v
C=20.6v

T7 i have 
E=42.7v
B=42.9v
C=44.74v

and 15.4v from the 10m resistor to the junction with the 1g resistor.