FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[Khron]

Not really, no. More like, it affects the max undistorted SPL

 

[G-Sun]

Not really, no. More like, it affects the max undistorted SPL

Thanks!
Ok, then I can share my build

 

[G-Sun]

So, here is my Fet847

Featuring
- Original BM800 body and headbasket
- 3Uaudio GZT-47 transformer
- Capsule: http://www.wgtcenter.com/microphone-34mm-large-mylar-capsule-diaphragm-condenser-double-sided-m7-k47-k49-k87-mount-for-neumann-mic-diy-replacement-pro.html

Soundfiles:
https://www.dropbox.com/sh/e31qlgyopwphlar/AAAdPGuv_DK2bBDwCbxYpZFna?dl=0

Sorry for not having an LDC to compare with, and for some noise on my ssl9k ch2, and for bad performance (well, sharing anyway  )

Comparing with
Line Audio cm3 SDC
BIV1 ribbon mic, and
RE20 dynamic

What I hear: The Fet847 as I made it is a little strange sounding on vocal and guitar, not a favorite here.
But on djembe (and probably on more perc. it sounded very usable)

 

[Khron]

Does yours take 5mins (or more) to reach "full" level too?

 

[G-Sun]

Does yours take 5mins (or more) to reach "full" level too?

Can't seem to noticed there was anything like that.

 

[Wordsushi]

I made this PCB for my personal use only. Poctop is already selling a nice PCB for this project 

The Badge is from Frank Röllen (frontpanels.de) The quality is excellent.

I just built the Poctop board. I prefer the way your board implements the transformer.

 

[gearhunter]

Hi!
I am about to finish the build of my fet847 (I hope so) and I have two questions.

I have seen that the Cinemag CM-5722 has a copper foil for grounding the lamination. Should I do something with it or leave it as it is? I have seen that in some builds they have cut it.

Regarding biasing the fet, since I do not have an oscilloscope, I have chosen to use the computer as such without having had success. I have been able to modify the value of the variable resistor to obtain 10V at the drain using a DMM but I want to adjust the value of the resistance so that it adapts more to the FET I have chosen for the circuit.
What I have done with the computer has been to generate a 1kHz tone that has left the 1L output of my Audient ID14 to connect to the ground of the PCB and to the capacitor C1 connected to the FET Gate using a TS cable. To capture the signal I have simply connected the XLR of the circuit to the input of the card, which has provided the phantom. To do the routing and analyze the signal I have used Studio One with the plugins that it has as standard. (Tone Generator + Scope)

The problem I have is that the signal delivered by the microphone is so low that I have to raise the gain of the preamp practically to the maximum to be able to see a bit of the sine wave and I am not able to do the biasing process in these conditions. At least the circuit has not burned when the phantom was turned on. Does anyone have any idea what I'm doing wrong?

 

[Khron]

Have you considered turning up the output of your interface? And/or the levels in S1?

The tone generator plugin has an output level control, but it might not default to maximum.

You can't really "burn" anything, because phantom power is supplied through a pair of 6.8k resistors inside the preamp.

 

[gearhunter]

Yes, I can only see signal  when the output level of the tone generator and the output of my interface (I have checked the ID control pannel too) is almost all the way up.

 

[Khron]

What if you try recording some actual audio with the mic?

 

[gearhunter]

Problem solved!

To be able to bias the fet with the method I described with Studio One I had to disconnect R2 and C11 from the teflon pin

 

[francoisjonas]

hi, 
I just begin in the mic building and obviously i have a question

There is no more 2N3819 (semi conductor jfet) available on Mouser. So,i ask for another parts and we tell me the NTE312 -  JFET Transistor. BUT he 's also unavailable. As a noob I can't find another parts by myself and buy one in US is kind of expansive. Have you any alternative that I can find in europe ^^ ?

Thx a lot

 

[Max51]

Hi everybody !

There's still someone ?
Does someone still get a pcb for that project to sell ?

Thanks !

 

[Micmods]

Could we get a photo of the back of the board?

 

[Khron]

It's a secret!.. :

Not that anyone cares, but a while ago a whipped up a much cleaner layout within the same board outline.
Can't remember whether i did a second version too, without axial electrolytics, but i know i wanted to.

That being said, once both are done and "polished up" (silkscreen etc), i'll throw'em up on Oshpark or something.

Could we get a photo of the back of the board?

 

[Wordsushi]

It's a secret!.. :

Not that anyone cares, but a while ago a whipped up a much cleaner layout within the same board outline.
Can't remember whether i did a second version too, without axial electrolytics, but i know i wanted to.

That being said, once both are done and "polished up" (silkscreen etc), i'll throw'em up on Oshpark or something.

I care. I'd definitely build your version if you put it on Oshpark.

 

[Khron]

Duly noted ;D I still cringe when i see the dog's breakfast of a layout that the original is... 

I "even" managed to squeeze the whole thing onto a single layer (so that much easier to DIY).

I care. I'd definitely build your version if you put it on Oshpark.

 

[Strick9]

Duly noted ;D I still cringe when i see the dog's breakfast of a layout that the original is... 

I "even" managed to squeeze the whole thing onto a single layer (so that much easier to DIY).

I am also interested in one

 

[Khron]

I made a version that will fit BM800 bodies as well.

 

[shot]

Wow this is great!
Any chance you would share printable etch file or Eagle's BRD file for a (small) bunch of us home etchers?



Luka