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

[vinylwall]

I've built three of the D-U47FET's.  I put an Advanced Audio AK47 in the 1st, a Peluso P-K47 in the second, and a Microphone-Parts RK-7 in the third (not yet finished building).  I used AMI's T49 transformer in all three.  There is a sound clip above somewhere with the first build.

 

[saint gillis]

Hi,
My mic sounds really great, but time to time I ve got a small amount of a kind of red noise appearing, it is an intermittent problem, do you have an idea about why? (the capsule..?)
..

 

[poctop]

i would definively check you HZ section at the Fet on the isolation pin  for cold solder ,
reheat this part if anything ,
hope this helps,
BEst,
DAn,

 

[saint gillis]

It looked quite solid.. but sure I will check it carefully! thank you for this advice..

 

[saint gillis]

Hi again, so I re-soldered  the Hi-Z spot..
But then I had some big hum, I realised I made a ground loop when mounting back the body, so I fixed it, now it's good but I have a new problem, after 5 or 10s, the sound dissappears completely... I checked the voltages :
http://hpics.li/a97737e
A strange 44,6v instead of 21,5v at B point... Any idea about what's going on?

 

[poctop]

Hi again, so I re-soldered  the Hi-Z spot..
But then I had some big hum, I realised I made a ground loop when mounting back the body, so I fixed it, now it's good but I have a new problem, after 5 or 10s, the sound dissappears completely... I checked the voltages :
http://hpics.li/a97737e
A strange 44,6v instead of 21,5v at B point... Any idea about what's going on?

what is the configuration of the 220M resistor is it 200 + 20 or 220M and if it is 220M only did you solder to no r+ pad as described in the build.
send a picture of this section , 
Best,
Dan,

 

[saint gillis]

what is the configuration of the 220M resistor is it 200 + 20 or 220M and if it is 220M only did you solder to no r+ pad as described in the build.
send a picture of this section , 
Best,
Dan,

Damn not... I solder the 220M to the wrong hole...
I'm corecting that... Do you think it could have damaged something?

 

[saint gillis]

Ok I soldered the 220M resistor properly , but I still have the pbm of the sound switching off after 10s...

 

[poctop]

Ok I soldered the 220M resistor properly , but I still have the pbm of the sound switching off after 10s...

remove capsule and inject sine tone in the amp just before the fet coupling cap ,  2200pf IIRC,
this will rule out the capsule for contamination , and recheck voltage ,
Check for cold solder in the HZ bridge,
Best,
Dan,

 

[saint gillis]

remove capsule and inject sine tone in the amp just before the fet coupling cap ,  2200pf IIRC,
this will rule out the capsule for contamination , and recheck voltage ,
Check for cold solder in the HZ bridge,
Best,
Dan,

Ok, did what you said, so same voltages, and still same 44,6V at "B" point...
And concerning collector of T4 it takes about 20s on the voltmeter from 38v untill it reaches the voltage of 26,9V... (it was the same last time but I did not mention it) ...
Thanks for helping Dany!

 

[poctop]

remove capsule and inject sine tone in the amp just before the fet coupling cap ,  2200pf IIRC,
this will rule out the capsule for contamination , and recheck voltage ,
Check for cold solder in the HZ bridge,
Best,
Dan,

Ok, did what you said, so same voltages, and still same 44,6V at "B" point...
And concerning collector of T4 it takes about 20s on the voltmeter from 38v untill it reaches the voltage of 26,9V... (it was the same last time but I did not mention it) ...
Thanks for helping Dany!

if you missed this , I would suggest you check out the build guide just to make sure you haven't made a mistake with the lwire ink on both pcb,  check for leaky cap around T4 ,  and potentiometer configuration if you haven't used it or installed it ,
reverify transistor number and position ,
Hope this helps,
Dan,

 

[saint gillis]

Hi Dany,
So I'm an ******* for many reasons..
1st of all for having said the mic sounded great, because now that everything's ok it 's nothing compared than before, it's ******* amazing!
I replaced C7 & C8, but it changed nothing, then I changed all the bipolar transistors, it's not the way I like to fix stuff, but I lost patience... and now I discovered an amazing microphone, awesome!!!

 

[Biasrocks]

Project complete.

Badaax GT-2B for donor
RK47 Capsule
Cinemag Transformer

Easily completed in about 3 hours, powered up and worked from the hop.

Mark

 

[Biasrocks]

Another shot.

 

[Biasrocks]

Another shot.

 

[Biasrocks]

One more.

 

[Biasrocks]

Here's a quick drum recording I did to showcase what the 47FET brings to the party.

Photo's

https://www.dropbox.com/s/szj92zha84vwz6q/IMG_0991.JPG?dl=0
https://www.dropbox.com/s/gu56yqu96whrp1x/IMG_0992.JPG?dl=0

Audio 24/88kHz, RE20, U47FET Kick, SM57 Snare, U87 Overheads,
No EQ or processing aside from some parallel compression.

Full kit w/47FET
https://www.dropbox.com/s/1hvhmnk897chd4x/Drums-U47FET-All.wav?dl=0

Full kit wo/47FET
https://www.dropbox.com/s/inaqlkg8wtavv87/Drums-U47FET-Off.wav?dl=0

47FET  Solo
https://www.dropbox.com/s/bxjp19z3qtia3nv/Drums-U47FET-Solo.wav?dl=0

RE20 Solo - Inside Kick
https://www.dropbox.com/s/95b1n3i6r8syt9j/Drums-RE20-Solo.wav?dl=0

RE20 47FET Combined
https://www.dropbox.com/s/eiyxhv9b89m3w5v/Drums-RE20-U47FET-Solo.wav?dl=0

FULL KIT Processed
https://www.dropbox.com/s/gt7hfsi5ex7ie46/Drums-Processed.wav?dl=0

Mark

 

[Matt55]

Hello Dany,

So I have just started populating the board and realised Mouser made a cock up on my order and missed some of the parts out of the BOM!

I have ordered the parts that were missing so I am waiting for them, not a problem as I uave my U87 to be finishing off.

I have a few questions regarding the build;

1) I noticed there are many additional parts for BC5578 and BC5478. What is the aim here? Do i need to measure them like the JFET in the U87 build and pick a certain on based on their measurements? Should they be as similar as possible etc??

2) Resistors (R18+R19) and (R20+R21) also have additional parts. Do these need to be matched within a certain percetage like the ones in the u87 build? I can use a wheatstone bridge like i did there if thats what they need? What percentage do they need to be matched to?

3) On the schematic the Styrene at C2 reads 18pf, the one from you has 20K printed on it? Is this ok?

4) On the schematic R5+ and R5 suggest 33M or 2x68M, the one in the BOM is 30M. Is this ok?

Thanks for creating these builds they are quite marvelous I cant wait to get both my U87 and U47FET working and in use in my studio

Regards,

  Matt

 

[poctop]

Hello Dany,

So I have just started populating the board and realised Mouser made a cock up on my order and missed some of the parts out of the BOM!

I have ordered the parts that were missing so I am waiting for them, not a problem as I uave my U87 to be finishing off.

I have a few questions regarding the build;

1) I noticed there are many additional parts for BC5578 and BC5478. What is the aim here? Do i need to measure them like the JFET in the U87 build and pick a certain on based on their measurements? Should they be as similar as possible etc??

normally you would check for highest HFE on these but they are already garanteed , so keep those as spare as those fairchild transisitor wont be here for muc much longer

2) Resistors (R18+R19) and (R20+R21) also have additional parts. Do these need to be matched within a certain percetage like the ones in the u87 build? I can use a wheatstone bridge like i did there if thats what they need? What percentage do they need to be matched to?
0.4%

3) On the schematic the Styrene at C2 reads 18pf, the one from you has 20K printed on it? Is this ok?
yes it is ok it is 20pf with 10% tolerance  =  20K

4) On the schematic R5+ and R5 suggest 33M or 2x68M, the one in the BOM is 30M. Is this ok?
if you have R5 at 30M this is ok use only R5  if you have 2*68M then use R5 and R5+ as they are in parralele

Thanks for creating these builds they are quite marvelous I cant wait to get both my U87 and U47FET working and in use in my studio

Regards,

  Matt

 

[poctop]

Hi Dany,
So I'm an ******* for many reasons..
1st of all for having said the mic sounded great, because now that everything's ok it 's nothing compared than before, it's f**king amazing!
I replaced C7 & C8, but it changed nothing, then I changed all the bipolar transistors, it's not the way I like to fix stuff, but I lost patience... and now I discovered an amazing microphone, awesome!!!

dont worry your not.....  .  everybody make mistake and this is where you learned the most when
i will have now to like your post for the second part of it , Thanks for posting ,
Best,
dAn,