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

[globalpurpose]

ignore the ugly transformer board...

Do You have a link or reference for this double mini switch ? very interresting

 

[kpergant]

I recently got AMI's FET 47 transformer and it came with green, red, black, and white wires. Does anyone happen to know the corresponding pads on Dan's pcb? Thank you for any help.

Did you ever figure out the answer to this? I am in same situation. Thanks.

 

[geekmacdaddy]

Did you ever figure out the answer to this? I am in same situation. Thanks.

Here is the wire colors for their BV8 Classic...

 

[kpergant]

Thanks so much! I wonder if it works the same on the FET 47 transformer. I hear AMI are not very thoughtful in their coloring of their wires. I do appreciate you helping me at least see another AMI diagram with colors listed. How did you like the sound of your BV8?

 

[Cqwet Dbdfte]

Coloring in electronics is arbitrary except for (some) thru hole resistors and some ribbon cables.
There is no convention or standard for transformer leads, that's what data sheets are used for. Download data sheets for each and every part you buy for your builds, and read thru them.

 

[neowalla]

What are your thoughts on the practicality of making a U48, multi-pattern from these PCBs?

 

[Friedemann]

Hey!
Could You please tell a source for the 220MOhm (or 200M and 20M) / 1W resistors!
I am located in germany…
Thanks and bye Friedemann

 

[garp]

Just a silly question, looking at the original design i found that many polarized tantalums have been replaced either by electrolytics or film caps in the suggested BOM, is there a reason ?
Is it also possible to replace the 2,2 uf at C5 with a 10uf ? As far as i understand the schematic is it only here for decoupling ?

 

[Sebass]

Hi everyone,

I've got a couple of questions about my current mic build, and I hope someone can shed some light on them without me having to read through the entire thread.

Firstly, why are the transistors (T3) to (T7) connected in series? Was this done to mimic the tonal characteristics of a tube?

Secondly, my mic is producing a bit of noise. I suspect it might be related to the 200 Megaohm resistor (R2) I'm using. It's a high-voltage resistor I bought from Mouser Electronics because they didn't have a smaller one available. A search across the internet didn't yield any results either. I've attached a picture showing the soldered resistor. Does anyone know if this could be causing the noise, or where I might find a more suitable resistor (as Friedemann asked in 2 posts above)?
The resistor I used:
https://www.mouser.de/ProductDetail...=sGAEpiMZZMtlubZbdhIBIPKfOsN7He4BuRTQARBw984=

Thanks in advance for your help!
Sebass

 

[Cqwet Dbdfte]

https://www.digikey.com/en/products/detail/stackpole-electronics-inc/MGM3JT220M/17622082

carbon film resistors and tantalums? Why?

 

[klem]

Hi everyone,

I've got a couple of questions about my current mic build, and I hope someone can shed some light on them without me having to read through the entire thread.

Firstly, why are the transistors (T3) to (T7) connected in series? Was this done to mimic the tonal characteristics of a tube?

Secondly, my mic is producing a bit of noise.

Thanks in advance for your help!
Sebass

transistor config is beyond my knowledge, but re: noise, the first thing I'd think about before type of R (carbon vs. metal film) are contaminants on the high Z area where R2 is located. 99% isoprop and q tips etc is standard advice for cleaning. I do wish there was a way to put the area under a camera, microscope or analyzer of some sort to know when it's clean enough - anyone have any insight here?

EDIT - @Sebass I just saw your photo, in case you aren't aware, styrene capacitors are not good bedfellows with ETOH, so proceed cautiously. It *may* be easier to just take them out of the circuit so you can go to town with cleaning, but also there's a risk of damaging the thin leads on those caps with excessive force or heat, so either way, be careful!

As for sourcing R2 (220), this is covered in the thread, lots of valuable info. (I do wish more knowledgeable folks would weigh in for some of the intermediate questions like a walk-through of the function/role of each capacitor with focus of component sub like @garp C5 or @klem C6 are wondering.

Anyway, for R2, just order two values that sum to 220M R. I.e.,
https://www.mouser.com/ProductDetail/279-RGP0207CHJ100M
and
https://www.mouser.com/ProductDetail/279-RGP0207CHJ120M
and wire them in series, making sure the overall height is allowing for decent clearance of headbasket plate.

HTH,

 

[klem]

I am building a pair of these with one change, tantalums vs lytics and see which I prefer (if I can even hear a difference). In some places the substitutions are easy, but one in particular doesn't seem to have any options in the US48 - can anyone suggest an electrolytic sub for C6, .33uF, 50V+, LS 5mm? (It's marked polar on the board so I assume I can't use a BP or film cap)

 

[JamieOxford]

Hello, I'm repairing an early STAM U-47 FET for a friend and it turns out it uses these DU47FETi PCBs and what looks like the 3U capsules mentioned here.

It's having some problems with popping every 5-10 seconds (it sounds like the phantom power is disconnecting continuously so I'm assuming it's a bad capacitor or component). Does anyone have any experience with this?

The circuit on the mic looks slightly modded to accommodate the lack of pad and HPF as well.

Please find a few photos attached. Thanks!

 

[Rob Flinn]

Hello, I'm repairing an early STAM U-47 FET for a friend and it turns out it uses these DU47FETi PCBs and what looks like the 3U capsules mentioned here.

It's having some problems with popping every 5-10 seconds (it sounds like the phantom power is disconnecting continuously so I'm assuming it's a bad capacitor or component). Does anyone have any experience with this?

The circuit on the mic looks slightly modded to accommodate the lack of pad and HPF as well.

Please find a few photos attached. Thanks!

Did you try asking Stam ???

 

[JamieOxford]

Did you try asking Stam ???

He's already had it 'repaired' by STAM and it still has this issue… I think R1 or C1 are problematic so will look to replace those

 

[vinylwall]

Also, make sure the mic is grounded well.

 

[Rob Flinn]

He's already had it 'repaired' by STAM and it still has this issue… I think R1 or C1 are problematic so will look to replace those

I was suggesting asking them for the diagram, not to fix it..

 

[TLRT]

This is Dany's pcb,you can find the schematics in his DIY build topic.