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

[Hank Dussen]

Finished this one a few weeks ago.
Maiku K47 capsule and FAB V8f transformer.
The hardest part was fitting the transformer properly.
Also, I lowered the baseplate on which the capsule-holder sits to lower the capsule with 2 nuts. (see picture)
I know it's supposed to sit high in the basket but before lowering it, the capsule was 1mm from the top of the basket. That's too close for me.
So far I’ve used it on vocals and kick drum and it sounded excellent on both.

 

[jeid]

ok, so i "reversed" the connections on the T49 (A/B =xlr 2/3, and C/D=pcb 1/2) and...
plenty of bass ! beautiful sound !

so the folks at AMI put a sticker on the T49 to mark the A/B C/D, but they put it the wrong way ! (on mine) 
i would have preferred no sticker at all...
but i'm dumb, i measured the resistance of A/B C/D but did not noticed they were reversed ...

anyway, i'm happy now..
thanks a lot  ln76d for pointing the right direction !
(and thanks to poctop for this great mic, now i want another one !)

Just had the exact same issue with mine, thanks for this, saved me a whole lot of bother.

 

[ViciusbeatZ]

Greetings machines!
Comment that I acquired some PCB boards and I see that mine are a little different from the ones I see in the thread of the micro, in the picture that I attached I also have to make the connections in that way all to leg G, or I have to do it correctly since in mine yes that there are holes for the components?

Thank you very much!

 

[TillM]

Yes they are different cause you ordered your set from micandmod.

 

[ViciusbeatZ]

So you know if you have to mount it well in the holes? Or do we have to do the same with C3, the resistances and that?

 

[TillM]

Sorry I can’t help you.
The pcb design looks similar.
Seams like the turret is for the floating connection.
It’s better you ask micandmod.

 

[Hank Dussen]

This week I did some recordings for a band I play in and all of us were really impressed how good my D-U47fet (see a couple of posts back) sounded on anything we've put it in front of (soft female vocal, screaming male vocals, double bass, percussion, vibraphone, room,…)
just to let you know…  ;D

 

[shot]

I'm totally stuck with my mic!

After few days of troubleshooting I'm out of ideas what to do.
Voltage on B pad is oscillating from 2v to 44v. At first when mic is turned on it stays at 0v for about 15 seconds and then it starts going wild. I get sort of motorboating sound out of the mic.
Other voltages are also suspicious - for instance T4 has Vc-38v, Vb-10v, Ve-13v.
Voltage that is supposed to supply the capsule measured at pad A is 13.8v. Should that be higher?

I've checked if there is some wrong value/component present, after that I replaced T5, T6, T4... than I checked all board-to-board wiring, tried injecting sine signal at R1/C1 junction (used ceramic 68pf instead of real capsule)...

What else can I do?

What could be the cause of this oscillation at B pad?



Luka

 

[moamps]

Have you checked tantalum capacitors orientation and transformer connection?
What's going on with the voltage on emitter of T7 during  motorboating?
Voltage on Pad A is high-ohmic source so you can't measure it correctly with a standard DVM.

 

[shot]

Tantalums are correctly oriented... unless there's a print error on them!
Transformer is also correctly oriented. But I found on this thread that even when transformer is upside down it would still produce sound, even though that would be low volume and lacking bass... So I guess this is not a problem.

Voltages on T7 are Vc=44.1, Vb=42.5, Ve=42.5
Emmiter and base voltage drift a bit when mic is oscillating, like +/- 0.3v

I'll do a test to replace C6, C8 or C10 tantalums with electrolytic caps. One by one. Maybe there's something with one of those...



Luka

 

[shot]

I did it! Fixed it!

How? Well I don't know?
I've swapped T2 and FET, and also I swapped all the wires that connect two boards.
I'm sure that the problem was not in those wires since I tested their continuity few times, but since I desoldered them few times they were all burned up and looked ugly.
This was the third FET I've put into it and could be that previous two were somehow faulty.
Or it was transistor T2... don't know...

Mic sounds very nice! I'd say fantastic, but wait 'till I try it in the studio. For now I only tried it on the bench speaking blablabla into it. Very detailed mids and bottom end!

What I noticed is that it's output is significantly lower than two previous mics I've built (G7 and Ela m 251). But that's fine.
I'm using GZT-87 transformer (9.5:1) and K47 capsule from Banzai's group buy couple years ago. It's in the donor body bought from Chunger's shop (GT-2B)

Also, I've noticed that capsule mount provided with donor body is too high! When the capsule is fitted, metal bar that connects the grille was right at the center of the capsule. And capsule was too high, only few millimeters from the top grille. When I changed to low profile mount I think sound changed a bit. For the better of course!
So just as a tip for other builders, if you use this body be sure to check where your capsule is when assembled. Maybe order a low profile mount along with donor body at the beginning since it's cheap and could come in handy.

In the end... thank you Dan, thank you Moamps and entire community!



Luka

 

[ViciusbeatZ]

Regards! a silly question .... the black cable of the cinemag transformer cm-13101, what is it for? I am a beginner and it is my first micro, thank you!

 

[boomfred]

It’s ground.

 

[ViciusbeatZ]

ok! and i connect to the gnd of the pcb o other site?

 

[boomfred]

Indeed

 

[ViciusbeatZ]

Regards ! I finished the microphone and it does not work, the connections of the cinemag transformer are fine so on the pcb? and the capsule? Thank you!

 

[ViciusbeatZ]

connection capsule

 

[ViciusbeatZ]

general capsule

 

[ViciusbeatZ]

any help!! please!!

 

[TillM]

this is not the PCB from Dan.
The connection from the Cinemag you find in this thread, just search for it.
It's hard to tell, when you not tell us what don't work ?
Check all your soldering, transistor positions and resistor values first.