FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[Khron]

If / since you already use Eagle, surely the layout's trivial enough to manually copy / recreate it, isn't it?

I stuck to 0.1" (2.54mm) pitch for everything (if memory serves), so no "rocket surgery" going on here.

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

 

[shot]

If / since you already use Eagle, surely the layout's trivial enough to manually copy / recreate it, isn't it?

I was already about to do that last night but I was too tired after long day work and fell asleep!

8)

L

 

[Micmods]

Hi Mate

What program did you use for the PCB design. I have a cnc here set up to cut out pcb's. Would love to give your design a go if I could get the correct gerber / gcode

 

[Khron]

Hi Mate

What program did you use for the PCB design. I have a cnc here set up to cut out pcb's. Would love to give your design a go if I could get the correct gerber / gcode

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?

 

[dasnevestheo]

Hey !
Anyone tried this one here ? https://www.ebay.fr/itm/3U-Audio-GZT-84-Output-Transformer-for-SDC-Microphone/112882929558?hash=item1a4858cf96:g:CiYAAOSwW5lasiBg
7:1 ratio seems fine as original.
Also this circuit from Mic parts looks strangely similar : https://microphone-parts.com/products/t-84-circuit-kit am i right ?
If so, coupled with a RK12 capsule from rayking should turn into something like the mic parts T12, which is a truely incredible mic (compared in a professional studio with Thousands$$ mics)

 

[Max51]

Hey !

Anyone tried this one here ? https://www.ebay.fr/itm/3U-Audio-GZT-84-Output-Transformer-for-SDC-Microphone

Yes I did.

If so, coupled with a RK12 capsule from rayking

I did exactly that. I used 3U Transformer and RK12 from rayking capsule with BM800 donor mic.
It sounds good. I haven't really compared to some great mics, and for the moment I only used it on Voices and Guitar Amp.

I really like that mic on men voices. I got warm and deep sounds. Howewer, sound still accurate.

So, I think it's a good matching.

I will try to put more details later, with more hindsight.

 

[dasnevestheo]

Thanks a lot, would love more details indeed

 

[shot]

I have strange problem with my build!

Since I've built this mic around 6 months ago, I've had to replace FET twice! It just died during the recording session. Microphone would slowly during aprox. 5 minutes go into distortion and than it would shut itself down.
Both times fix was to replace the FET.

Now I'm thinking what could be wrong? Where do I find the root of this problem?
It didn't happen on the same preamp so I assume it's not faulty phantom power delivered by the preamp.  Other mics work well on all those pres.
In one situation I was using the mic on bass amp so the source SPL was high.  But in the next situation it was during relatively quiet voice over session.  Can it be that high SPL kills it?
Any other idea?

I'll swap the FET again and see how it goes. But now I'm pessimistic and I'm somehow sure it will die again in some time

It's Dany's pcb, chinese K47 capsule from the group buy, 3U transformer, FETs bought from Mouser... every component by the BOM and no funky component replacements...



Luka

 

[midwayfair]

The only thing I've ever seen kill a FET or most any other silicon transistor is running too much current through it, but you'd be looking at really, really, really small resistances on the drain and source, like less than hundreds of ohms, and you'd probably burn those resistors if that was also killing the transistor. You'd also smell smoke ...

High SPL shouldn't do anything except distort things.

Are you SURE the FETs are dead? Like you tried them on a breadboard or tester or something afterward and confirmed that they're kaput? Maybe replacing the FET just somehow temporarily corrected a problem elsewhere.

 

[shot]

Are you SURE the FETs are dead? Like you tried them on a breadboard or tester or something afterward and confirmed that they're kaput? Maybe replacing the FET just somehow temporarily corrected a problem elsewhere.

That's what I've been thinking whole day! Maybe it's not dead.
Yesterday I replaced with new FET but I didn't throw away the previous one. It's bugging me why don't I put it back and do some tests to find out what's going on.
I'll play around with it during the weekend.
I must win this battle!



Luka

 

[doqmemory]

That's what I've been thinking whole day! Maybe it's not dead.
Yesterday I replaced with new FET but I didn't throw away the previous one. It's bugging me why don't I put it back and do some tests to find out what's going on.
I'll play around with it during the weekend.
I must win this battle!



Luka

Did you win?

 

[shot]

Of course I've won!  8) 8)
It turned out it was a bad batch of fets! I bought them in a local shop. Seemed legit. Fairchild brand. Then I ordered few OnSemi branded fets online and left the first one in the circuit. It worked immediately!
If you google datasheets for fairchild and onsemi fets you can notice that their pinouts are different!



Luka

 

[Rybow]

Great that this is an active thread! I just received some 2n3819’s I ordered on eBay today to rebuild the p2p version I did ages ago. Made some layout mistakes on that one.

Now to source a signal generator kit

 

[Ricardus]

Great that this is an active thread! I just received some 2n3819’s I ordered on eBay today to rebuild the p2p version I did ages ago. Made some layout mistakes on that one.

Now to source a signal generator kit

I have yet to see any real 3819s on eBay.

 

[Rybow]

I have yet to see any real 3819s on eBay.

Uh oh. How do i tell?

 

[Khron]

Not sure I ever understood what's so special or "magical" about that particular part

 

[Rybow]

Not sure I ever understood what's so special or "magical" about that particular part

Neumann used it. Instant status elevation.

I just find it easier to use whatever is in the schematic.

 

[Khron]

And I'm willing to bet they used it because they didn't have all that much to choose from, back then. But hey, logic / common sense is tough to handle (?) ;D

Neumann used it. Instant status elevation.

I just find it easier to use whatever is in the schematic.

 

[Rybow]

And I'm willing to bet they used it because they didn't have all that much to choose from, back then. But hey, logic / common sense is tough to handle (?) ;D

That’s probably accurate. Also, if the goal is to get the sound as close as possible, is there really any other option?

From my searching I can’t find a clear answer as to a direct substitute for this JFET. NTE312, 2n4417 and MMBF5484 have been mentioned as possibilities,

 

[Khron]

How drastically different could they sound (they = 2N3819 versus it's potential substitutes, or other JFETs), provided they're all biased within their respective optimal operating regions? Discounting clipping performance, of course.