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Project Specific Discussions => Microphones => Topic started by: poctop on November 17, 2015, 03:55:25 PM

Title: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on November 17, 2015, 03:55:25 PM
The FET847 is an adaptation of a Vintage Neumann KM84 circuit designed by Jonathan Burtner  for LDC capsules in a small and economical donor body.

(https://www.dropbox.com/s/vdmomw1tt74odir/FET847.jpg?raw=1)

Items provided in this project:

● Circuit Schematic
● List of parts used in prototypes
● Mouser BOM
Here are some bullet points:
● KM84 circuit adapted for LDC use.
● This is a very simple circuit with minimal parts and a single FET for impedance conversion.
● The Mic can be assembled with one mouser order provided body, capsule, and transformer
are acquired via preferred 3rd party.
● As designed can be hardwired Cardioid or Omni.
● Cardioid wiring only uses one side of the capsule while omni uses both sides.
● Floating Hi-Z
jumper or switch may be added for switched card/omni operation or rear
diaphragm can be soldered to the FET gate for permanent omni operation.
● Designed for use with LDC k47, M7, or CK12 style flat large diaphragm capsules.
● Very similar to vintage U87 circuit without the de-emphasis
portion and different
transformer..
● New Cinemag CM5722
transformer is 7:1 for original KM84 ratio.
● U87 uses the 10:1 with essentially the same FET driver circuit so those can also be used for
lower output and different needs.
● 2n3819 FET should be selected and biased using the same methods as a U87.
● Efforts were made to keep the PCB small and “feature light” to provide a simple high quality
Mic with flexibility regarding primary build options such as capsule and transformer
selection.
● Donor body selection may require mounting HW to fit the PCB but it is designed to fit a BM800 in this
revision.
● BM800 Donor Body Accept HT11a Sized head basket
● Transformer also fits in the BM800 and is secured using E6000 adhesive.




Schematic Poctop
 https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a088b8.pdf

Schematic JB
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a088e3.pdf

Schematic KM84
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a088f4.jpg

Circuit Description
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a08905.pdf

BOM Mouser Link
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f72374e439

BOM Description and Hints
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a08916.pdf

Cinemag 5722 Diagram
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a08927.pdf

Cinemag 5722 Footprints
https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a08938.pdf



PCB
(https://io.groupdiy.com/file/gdiy-2017/u/39511/58d028199484e.jpg)

Enjoy ,

PM me if interested

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: tskguy on November 17, 2015, 08:24:21 PM
Super cool!!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on November 17, 2015, 10:58:14 PM
How does this compare to the 47Fet?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on November 18, 2015, 10:10:55 AM
How does this compare to the 47Fet?

It's different. This is more like a KM84 with an M7/K47/CK12 capsule... Or sorta like a U87 with a flat impedance converter (no de-emphasis).

I haven't put one in front of a kick drum yet but I will :)

Cheers!
-jb

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on November 18, 2015, 11:15:39 AM
How does this compare to the 47Fet?

It's different. This is more like a KM84 with an M7/K47/CK12 capsule... Or sorta like a U87 with a flat impedance converter (no de-emphasis).

I haven't put one in front of a kick drum yet but I will :)

Cheers!
-jb

Right, but if a 47fet is a k47 capsule with a fet amp into a transformer, isnt a km84 with a 47 capsule very similar? 

I have an extra k47 hanging around and was about to order parts to build a D-47FET.  IT seems like the 84 will be a little cheaper due to the lower parts count, although I haven't seen a price on the new cinemag transformer.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 11:35:48 AM
looks pretty promising. Any idea of the board cost?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: kidvybes on November 18, 2015, 12:00:20 PM
...inexpensive sources for BM800 body/shockmount:

http://www.aliexpress.com/item/Microphone-Professional-Studio-Microphone-BM800-Wired-Microphone-Sound-Recording-Condenser-Karaoke-Mic-Stand-Holder-for-computer/32465243530.html

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: kidvybes on November 18, 2015, 12:02:47 PM
...choices:

http://www.aliexpress.com/item/BM-800-Condenser-Sound-Uni-directionalcondenser-Recording-Microphone-with-Shock-Mount-for-Radio-Braodcasting-Sound-Studio/32461235648.html
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 12:03:19 PM
I already have one at home and was going to build a Schoepps circuit on strip board. Maybe I should change my ming hehe 8)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on November 18, 2015, 12:31:12 PM
AMI's T8 also fits the BM800 body (same size as the CM5722) if you want to think of it like a U47 with a single FET instead of a tube. However not a FET47 or a U47.... Nor is it really a KM84.. :)
http://www.tab-funkenwerk.com/id75.html
I have only used the CM5722 though.

This build has transformer options as well as capsule options and isn't necessarily intended to be a KM84 clone since the capsule is different anyway... Consider that a U87 uses the same fet with the same operating points and the transformer in a U87 is different ratio as well...

Some additional notes:
- The bias trim pot has a jumper so that once you know the R3 value (FET Bias) you can order a more permanent precision resistor and jumper that resistor into circuit.
- As designed it's hardwired cardioid only or omni only. It might be possible to float a jumper or switch for pattern switching. I am working out a solution for a possible switch but didn't feel that it was really a design requirement.
- Since there is only one PCB there may be room to install a larger PIO (not too large mind you) for the output cap on the back-side. I've got some on order to see if I can make them fit and I'm hoping they do fit!
- Dany also made provisions on the PCB to fit styro's in the regular places if desired.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: kidvybes on November 18, 2015, 12:48:51 PM
AMI's T8 also fits the BM800 body (same size as the CM5722) if you want to think of it like a U47 with a single FET instead of a tube. However not a FET47 or a U47.... Nor is it really a KM84.. :)
http://www.tab-funkenwerk.com/id75.html
I have only used the CM5722 though.

I have the AMI T8 in a 251-inspired FET build and it sounds terrific...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 01:14:53 PM
I would be curious to know the tone of the mic with a K47 type capsule. I was planing building a pair of U87 for Room miking but, that one make me think that I could build them instead.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 01:15:20 PM
oh and I just ask Cinemag and the transformer would cost about 59USD
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 02:25:32 PM
I guess the SCM900 would work, too. Just more room Inside the body. I got 2 of them here, maybe they could work. Do you have the measurement of the board Dany?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on November 18, 2015, 02:26:11 PM
Dims  ;)

(https://io.groupdiy.com/file/gdiy-2017/u/39511/58d028199485d.jpg)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 02:46:19 PM
Thanks. Once I got my SCM900, I'll take a look at the rail to confirm how it would fit. I think I'll go with a pair of FET847 and built them Inside the SCM900. Their will be enought room to put some bigger caps  8)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 03:12:22 PM
Is the board double side, so we can some component on the bottom side?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on November 18, 2015, 03:17:29 PM
Is the board double side, so we can some component on the bottom side?

Yes it is 2 layer,
Best,
Dan
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: RuudNL on November 18, 2015, 03:27:45 PM
What is the function of C1 ("Tuned to taste")?
How do we "tune" this?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on November 18, 2015, 05:15:22 PM
What is the function of C1 ("Tuned to taste")?
How do we "tune" this?
C1 as in the 4pF NFB cap? That cap certainly provides some NFB back into the gate portion which in my understanding stabilizes the amp, reduces gain, and I believe it also reduces output impedance... I'll read up in my RDH4 on NFB maths...
For tuning the specific value try some different values, sweep the DUT / graph the results for quantitative measurements, listen in context for qualitative measurements...
I don't know of another procedure used by the OEM but would like to hear about it if anyone knows or any additional discussion on the topic for that matter.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 18, 2015, 07:58:03 PM
Svm900 will fit :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on November 19, 2015, 07:50:22 AM
What is the function of C1 ("Tuned to taste")?
How do we "tune" this?
C1 as in the 4pF NFB cap? That cap certainly provides some NFB back into the gate portion which in my understanding stabilizes the amp, reduces gain, and I believe it also reduces output impedance... I'll read up in my RDH4 on NFB maths...
For tuning the specific value try some different values, sweep the DUT / graph the results for quantitative measurements, listen in context for qualitative measurements...
I don't know of another procedure used by the OEM but would like to hear about it if anyone knows or any additional discussion on the topic for that matter.

Cheers!
-jb


our Best Friend Oliver Used the Mic,  a Room and,  Acoustic Piano to tune Those.
Best,
Dan,
 
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 19, 2015, 08:29:24 AM
For your information, Advanced Audio carries some headbasket replacement.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Gus on November 22, 2015, 01:38:08 PM
Schematic looks like something Flatpicker posted years ago. 

It is all in the details

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on November 24, 2015, 01:01:06 PM
Is it best to order the transformer direct from cinemag?  I can't find it anywhere...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on November 24, 2015, 02:01:04 PM
You have to ask David from cinemag directly, the transformer isn't listed on their website
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: geebeeVIE on November 29, 2015, 05:50:56 PM
Sorry for the dumb question,  but what polarization voltage does it supply to the capsule?

If it does supply, like the KM84, only "less then 48V" - it will not be suitable for any of the mentioned capsules as they ask for 60V polarization voltage to work to their specifications....
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on November 29, 2015, 06:59:27 PM
Sorry for the dumb question,  but what polarization voltage does it supply to the capsule?

If it does supply, like the KM84, only "less then 48V" - it will not be suitable for any of the mentioned capsules as they ask for 60V polarization voltage to work to their specifications....
That's a great observation and yes the polarization voltage supplied to the capsule is in the area of "slightly less than 48V" like the KM84 or vintage U87 circuits which both use different capsules biased at that voltage. It is my understanding that the 60V (or perhaps even 70V) polarization spec is a max value before the diaphragm becomes sucked to the backplate due to electrostatic attraction.

The slightly lower polarization voltage does at least two things - It creates slightly less tension on the diaphragm and it slightly reduces the signal level from the capsule into the FET. In my tests the mic is very quiet and has more signal output than a vintage U87.

In reference to capsule specifications and polarization voltages I would like to point out that in many tube mic designs with variable patterns (for instance) that the rear diaphragm will see 0-120V depending on the selected pattern, the backplate will see a fixed 60V, and the front diaphragm will see 0V so if you have one of these tube mic's that uses that type of pattern adjustment and you would like to perform some polarization / sonic tests you could ground the front capsule (instead of connecting it to the grid), and use only the rear diaphragm with the variable bias / rear-diaphragm-voltage.

Cheers!
-jonathan
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: bruno2000 on November 29, 2015, 07:49:17 PM
I have a collection of U64 mics (which I love), and consequently have a stash of NOS 7586 tubes.  Thought about doing something like this with a 47 or 49 capsule, but using the 7586 tube.  Thoughts?
Thanks!
Best,
Bruno2000
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on November 30, 2015, 11:24:49 AM
I have a collection of U64 mics (which I love), and consequently have a stash of NOS 7586 tubes.  Thought about doing something like this with a 47 or 49 capsule, but using the 7586 tube.  Thoughts?
Thanks!
Best,
Bruno2000
I think that would turn out similar to the original with the 7586 paired to the BV107 / CM5722 from Cinemag in what looks like a fairly standard plate-loaded self-bias circuit (close-to-stock chinese PSU would work well since it's not fixed bias). You could change the polarization scheme slightly such that you polarize the backplate and take the signal directly from the diaphragm while losing the capsule-to-grid blocking cap. Looks like the U64 uses a 51V capsule polarization divided down from 120V so you could also tune that as desired :) You could probably P2P it pretty easily too in a small body like this one for tight placement and a fixed omni/card pattern too.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on November 30, 2015, 10:03:25 PM
Only  10 Left ,  :o
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 01, 2015, 04:06:20 PM
Be patient, I'll come with at least 4 of them soon :D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on December 01, 2015, 04:26:18 PM
only 6 Left ,
Best,
Dan,
 :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on December 02, 2015, 08:06:53 AM
2 Left , and this is it ,
Best,
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on December 02, 2015, 09:21:18 AM
KDOKELeeDO,   all gone ,  :'(
thanks To All and Enjoy your FET847 Project ,
Best,
Dan,

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 02, 2015, 09:40:07 AM
KDOKELeeDO,   all gone ,  :'(
thanks To All and Enjoy your FET847 Project ,
Best,
Dan,

Now we have to get enought interest to start another batch   ;D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on December 06, 2015, 12:35:28 PM
might be a silly question but why is there 22uf tant in the BOM? C9 optional tantalum?

regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on December 07, 2015, 11:16:29 AM
80-T350D226K006AT T350D226K006AT Kemet Tantalum Capacitors - Solid Leaded 6.3volts
22uF 10%

C2 (more bass option) 1

Best,
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on December 07, 2015, 01:52:29 PM
Ah ok,

So could that be put to a switch and tuned to taste for bass?

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 07, 2015, 02:02:32 PM
Ah ok,

So could that be put to a switch and tuned to taste for bass?

Spence.

You could put some socket (kinda dip socket) and simply swap different caps value to find out which one you prefer. Croc clip could be used to try them out, too
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on December 07, 2015, 03:47:11 PM
That cap bypasses the gate bias degenerative feedback portion with an HPF so the higher value pushes the HPF down in frequency causing less low frequency roll off and less phase issue around the corner frequency and above.

I believe the U87 uses a 20u cap in that position while the KM84 uses the 4.7u to prevent saturation in the OPT.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: felixskw on December 14, 2015, 10:07:01 PM
Any plans for a next batch?

Cheers,
Felix
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 15, 2015, 07:50:01 AM
Any plans for a next batch?

Cheers,
Felix

If there is enought interest  8)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: felixskw on December 15, 2015, 11:26:40 AM
Count me in :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: geebeeVIE on December 19, 2015, 06:23:28 PM
is there any way to increase the output level /gain of this circuit?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Ampampam on December 20, 2015, 05:10:56 PM
You should time the next turn to the same time with the chineese capsule group buy, and we could all build the ulitmate chineese diy mic!    8)

If the group buy is done, I'm in for 2 sets.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 22, 2015, 06:52:47 PM
D847 into à scm900 body.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 22, 2015, 06:54:41 PM
Dany's M7 capsule and cinemag cm5722
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 22, 2015, 07:02:39 PM
is there any way to increase the output level /gain of this circuit?

Not really, unless you feed it with some 68v or so. Thé km84 has à sensitivity of about 8mv/pa, same with à vintage u87. À modern mic run about 20 to 28mv/pa. Quiet à good step between. You need à good and clean premp to be able to run it clean, sincères you'll have to open up thw gain quiet more than à modern mic. It's à good time to drive your fav pre :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on December 23, 2015, 03:37:59 AM
could you put up some comparison sample between the DU-87?

regards

Spence.

p.s. i still haven't built my 2 x FET847
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 23, 2015, 06:02:10 AM
could you put up some comparison sample between the DU-87?

regards

Spence.

p.s. i still haven't built my 2 x FET847

Unfortunatly i sold my d-u87 so i can't do any comparaison. It's a wonderful microphone and highly customisable.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on December 23, 2015, 07:44:29 AM
I'll try and put up some comparisons once I've finished the 847 then.

Regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on December 23, 2015, 09:42:42 AM
Dany's M7 capsule and cinemag cm5722

Very clean and tidy build and I hope you are enjoying it!

Cheers,
jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Deepdark on December 23, 2015, 10:29:52 AM
Dany's M7 capsule and cinemag cm5722

Very clean and tidy build and I hope you are enjoying it!

Cheers,
jb

Of course I do.

Little thing to take in consideration:

While mounting the Hi-z floating section, do not conect resistors and caps behind the board. If so, the leads are touching the pad and there is some leakage due to the hi-z and it causes a little hiss. I'll make a build manual so people will have a step by step guide of how to build this little bad boy :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on December 23, 2015, 10:46:40 AM
Best to install the Hi-Z side of those 1G's and the 0.1u film cap (or styro if that's what is preferred) directly to the teflon standoff. I did it on the front side of the PCB (cleaning off any flux) and everything was very quiet.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on December 23, 2015, 03:31:54 PM
Glad to hear I did the hi Z resistors the right way on the front...  This is my first mic build, so I was a little confused in a couple places. 


(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.00.52_zpsflucbk6o.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.02.26_zpsf89whv6a.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.12.37_zpszekk8n4k.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.14.31_zpsqh0nbnbg.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.32.42_zps26fibpms.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.00.41_zps3xm3rqiz.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.00.48_zpszvmjy2mv.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.01.07_zpswgnluavt.jpg)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on December 23, 2015, 04:25:42 PM
Glad to hear I did the hi Z resistors the right way on the front...  This is my first mic build, so I was a little confused in a couple places. 


(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.00.52_zpsflucbk6o.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.02.26_zpsf89whv6a.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.12.37_zpszekk8n4k.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.14.31_zpsqh0nbnbg.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2020.32.42_zps26fibpms.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.00.41_zps3xm3rqiz.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.00.48_zpszvmjy2mv.jpg)
(http://i235.photobucket.com/albums/ee224/rosenton/2015-12-18%2021.01.07_zpswgnluavt.jpg)

you could have actually used this hole to let the pin of the wima capacitor go to the other side of the board and make the floating connection form the back ,

(https://io.groupdiy.com/file/gdiy-2017/u/39511/58d028199487c.jpg)

this is why I had made this hole available ,

just a thought,
D ;)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 08, 2016, 09:25:37 AM
hi,

i gotta bunch of OEP A262 6.45:1 ratio txf lying around they look like they might fit in the body of the BM800?
gonna give them a go and see how they sound.

regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on January 12, 2016, 01:22:56 PM
Awesome and interested to see what you think about the OEP in that application. Attached photo of builds in progress :)

Cheers!
-jb

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on January 12, 2016, 01:25:17 PM
Also confirmed that this particular PIO does fit when mounted behind the PCB :)

Cheers,
jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on January 12, 2016, 02:11:05 PM
I finished mine over the weekend!

(http://i235.photobucket.com/albums/ee224/rosenton/2016-01-09%2011.22.01_zpsteowb7pm.jpg)

Put a 1K tone into the mic with the capsule not connected from my phone.

Took a look at this tone on  my scope:

(http://i235.photobucket.com/albums/ee224/rosenton/2016-01-09%2011.27.02_zpshgqqlcwu.jpg)

Adjusted the resistor to show this at the output of the microphone:

(http://i235.photobucket.com/albums/ee224/rosenton/2016-01-09%2011.23.39_zpsxi7creqe.jpg)



I used it to record acoustic guitar over the weekend, and I have to say I am very, very happy.  I've been having a rough time recording this guitar with a variety of mics, but the FET847 just sounded "right"

I wish it was a fig 8 mic so I could reject more of my vocals, but I guess you can't have everything!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on January 12, 2016, 03:53:20 PM
Are there supposed to be photos within the post?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Winetree on January 12, 2016, 07:56:52 PM
What capsule and transformer did you use?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: rockinrob86 on January 12, 2016, 09:21:21 PM
The cinemag 5722, and a microphone parts RK47.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: midwayfair on January 12, 2016, 10:56:43 PM
...inexpensive sources for BM800 body/shockmount:

http://www.aliexpress.com/item/Microphone-Professional-Studio-Microphone-BM800-Wired-Microphone-Sound-Recording-Condenser-Karaoke-Mic-Stand-Holder-for-computer/32465243530.html

It'll fit in this? I remember these coming up in a thread a while back, but I can't find it to see if anyone took measurements of the PCB rails.

EDIT: Also you can put me down for a PCB if you do another run.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: vinylwall on January 13, 2016, 07:15:37 AM
Hi Dany.  I'd pick up a pair of PCB's if you did another run.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on January 18, 2016, 08:27:00 PM
Another small run is now launched,
So if anything please post ,  :)
thanks,
Best,
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: fsalter on January 18, 2016, 08:34:27 PM
Yeah sure...a couple more for me Sir Poctop
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 19, 2016, 09:02:13 AM
I'm still waiting for some components and mic cases!! Seem delivery from China is very hit and miss at the moment!!!!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 19, 2016, 01:00:49 PM
These just arrived!
Time to get to work!

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 19, 2016, 08:59:18 PM
Well considering i've used the crappy capsules which come with the BM800 mics and i've used OEP A262A3E transformers in there, they sound pretty good!!
its a tight fit with the OEP in there and ive used a 8pf mica in one and a 150pf mica in the other as im still waiting for the 4.7pf mica to arrive.
S/N isnt great but that must just be the capsules, i will try a few other capsules along with other txf.

regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on January 19, 2016, 09:27:46 PM
Well considering i've used the crappy capsules which come with the BM800 mics and i've used OEP A262A3E transformers in there, they sound pretty good!!
its a tight fit with the OEP in there and ive used a 8pf mica in one and a 150pf mica in the other as im still waiting for the 4.7pf mica to arrive.
S/N isnt great but that must just be the capsules, i will try a few other capsules along with other txf.

regards

Spence.

What kind of capsule anfd TF ratio do you have in there,
is it electret capsule ?
has it been biased with scope method , as this will affect the gain

D.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: felixskw on January 20, 2016, 02:38:30 AM
Count me in for 2 please.

Thanks,
Felix
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 20, 2016, 05:18:53 AM
Hi,

Txf ratio is 6.45:1 and I don't know what type of capsule it is but it's really crappy Chinese one that the BM800 comes with.
Have adjusted FET with pot for symmetrical clipping.
Once I get some small transformer supplies I will be winding my own transformers.

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 20, 2016, 05:21:15 AM
Some info I found on the BM800's

I'm sure that everyone in the pro-audio business has noticed the sudden plethora of ridiculously cheap 'professional' capacitor microphones.....
Last week I spotted one at 15 quid; that includes VAT and postage! While my microphone collection is extensive, I couldn't resist the temptation so I bought one and spent a whole day testing it really carefully against the yardstick of my own design 'JM47' and 'TB47' as well as a handful of AKG, Shure etc.
Have you guessed it?? The results are far from 'rubbish'.
These BM-700 and BM-800 mics are well made in the Neumann style but with electronics optimised to work with anything that requires a simple cheap 'tie-clip' type of electret mic.
The actual capsule is a TSB 160A made by Transound. This is a cardioid response capsule with no electronics fitted. The FET pre-amp is mounted on a separate PC board in the mic body.
Performance? It's very good indeed. The response and the actual 'sound' of the mic has that expensive sheen; it is extremely 'flat' from below 20Hz up to 12K where it wriggles a bit. There is the characteristic small 'kick' at about 3.5KHz, common to many electrets where some phase effects cause amplitude distortion and give it a very slightly 'bright' sound, but on balance, I would be more than happy to use it on a vocal session. It's a worthy mic at any price.
Noise? It's actually just as good as most traditional capacitor mics and much better than any of my test electrets.
If I was starting a studio right now, I would want a good handful of these mics......
The only problem is that they come with a silly 3.5mm jack plug connection and I must admit that I cut that off straight away and designed a simple little circuit that would provide 12V DC supply from the standard mic-amp 48V phantom.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on January 20, 2016, 05:55:05 AM
I hate you...

Now i'm thinking of grabbing a few BM800's myself, even if only as body-donors ;D Found some blue ones for ELEVEN quid, w/ free shipping... Those "gold top" ones are a bit garish for me x)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on January 20, 2016, 12:09:41 PM
I wouldn't expect the stock BM800 electret TSB160A capsules to work well in this circuit but they should work well in some other circuits. Check out the micbuilders yahoo group for some very nice circuits and other info :) I have saved mine and plan to use them in some cool steampunk style fancy-schmancy mic's one of these days :)

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on January 21, 2016, 07:08:45 AM
Check Guys  these donor body (model from the main photo):
http://www.aliexpress.com/item/High-quality-condenser-microphone-two-model-head-for-choosing/32303588010.html
I ordered one and up few weeks i will let you know is it worth and if the dimensions are appropriate for the project.
I think about pair of FET 847 with k47 for ambience mikes etc.

Dan - could you post here or send me to PM the price for PCB?

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on January 21, 2016, 07:44:29 AM
The one with the more rounded-off corners on the headbasket looks a LOT like the Apex 435 / Alctron HSMC001 to me (i have two of the latter)...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: felixskw on January 21, 2016, 06:39:38 PM
Dan, I would like to know the price too, please.

Thanks,
Felix
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on January 21, 2016, 07:13:47 PM
PMed,
D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 22, 2016, 03:31:48 AM
Hi,

I have to say, now I've tweaked both these FET847 they sound pretty amazing, I've put in the following:
4.7pf mica
OEP A262A3E transformer
BM800 body
I'll put a link to a very quick test I did with them overhead of the drums, not even really in a precise position, but the stereo image is lovely and wide, the roll off seems to be pretty much perfect.
When used with a FET47 on kick, add a bit of compression to the FET487 and they sound really good.
I used a LA-3A waves plugin, compressing at about 3-5db.
The bass was recorded DI into one of my 1176 same as the acoustic guitar.
This link should work:


https://soundcloud.com/spencer-lee-horton/hiatus


Regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on January 22, 2016, 12:19:04 PM
Hi,

I have to say, now I've tweaked both these FET847 they sound pretty amazing, I've put in the following:
4.7pf mica
OEP A262A3E transformer
BM800 body
I'll put a link to a very quick test I did with them overhead of the drums, not even really in a precise position, but the stereo image is lovely and wide, the roll off seems to be pretty much perfect.
When used with a FET47 on kick, add a bit of compression to the FET487 and they sound really good.
I used a LA-3A waves plugin, compressing at about 3-5db.
The bass was recorded DI into one of my 1176 same as the acoustic guitar.
This link may work I don't know?


https://cdn.fbsbx.com/hphotos-xtp1/v/t59.3654-21/12503008_10153527888138495_1316709750_n.mp3/Hiatus.mp3.mp3?oh=439078de4dc9fc0406573dedc697b277&oe=56A463CE&dl=1



Regards

Spence.

That's great spence! Which capsule did you use and which source bypass cap?

Cheers!
-jb

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on January 22, 2016, 12:53:56 PM
Hi,
i used the capsule which came with the BM800 which is an electret and the Cap was a 4.7pf mica.

regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: afdobbert on January 24, 2016, 10:43:09 AM
Hello,

Please put me down for a pair of these!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Will F on January 25, 2016, 04:47:40 PM
Well I keep thinking about a pair of these, so I guess I need to ask for 2 of them from this next run. They just look too fun!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Le Roux on January 28, 2016, 01:51:34 PM
Hi

I will take two please!  ;D

Thanks
Neil
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on February 01, 2016, 02:50:36 PM
All Pcb's Model Back in Stock including the FET847 available here :

http://www.vintagemicrophonepcbkit.com/orders.html

Best ,
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: afdobbert on May 03, 2016, 11:35:16 AM
Hey spence,

Would you mind posting the inside of your build? I'm thinking of using the A262A3E transformer in my set, and I'd love to see how you were able to get it mounted inside.


Thanks!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Le Roux on June 04, 2016, 12:58:02 PM
Almost have a pair completed.
I added the switch for omni and cardoid but,  not sure where to put back plate wire? I see the two turrets for front and back of capsule.

Thanks
Neil
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on June 07, 2016, 04:13:59 PM
Almost have a pair completed.
I added the switch for omni and cardoid but,  not sure where to put back plate wire? I see the two turrets for front and back of capsule.

Thanks
Neil

Connect back diapgrame wire out of capsule to FD turret  for omni ,

hope this helps,
BEst,
Dan,

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: afdobbert on June 26, 2016, 06:05:15 PM
Hey,

Just wanted to say, I ended up building a pair of these and I used the 3U audio 9.5:1 87-ish transformer because I had two around not doing anything. The resulting microphone (with asian 47 capsule) sounds really nice--and you can't beat the price. Obviously the 87-type transformer makes the output quite low, but its not low enough to be noisy and I think these will make very nice overheads! I imagine the 3U audio 6.5:1 would also work (and is probably a better choice if you want this to be a vocal mic), but that company's stuff is so cheap you could just get both and see what you like.

I bought the k47 caps used from a friend, so I think my total cost per mic was, like, under 150 dollars.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on June 26, 2016, 06:31:41 PM
Try to find used beerdynamic little transformers or RFT. These sometimes are pretty cheap and the result is really satisfiing ;)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on June 30, 2016, 10:52:18 AM
Yeah - These have turned out to be really great on "everything". Very glad I've made a bunch am interested to hear thoughts from the group now that there are some builds out there on applications where they have worked well and not so great too.

Cheers!
-jonathan
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Winetree on August 31, 2016, 05:00:29 PM
I've got 4 of these built with 847 stuffed boards mounted in BM800 bodies.
I received 8 of the group buy capsules (4-47s and 4-C12s).
Which capsules should I use, I'm thinking all 4 - 47s, or 2 of each.
Should I use the cinemags transformers?
Any comments?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 19, 2016, 11:27:15 AM
Hey Everybody!
Long time lurker. First time poster. I'm seriously contemplating building this FET847 as my first Poctop board mic.

I have a question about biasing the FET. In the thread starter Poctop said:
The FET847 is an adaptation of a Vintage Neumann KM84 circuit designed by Jonathan Burtner  for LDC capsules in a small and economical donor body.

● 2n3819 FET should be selected and biased using the same methods as a U87.


So in Andrew Shaap's build (http://www.vintagemicrophonepcbkit.com/Neumann%20U87%20Build.htm), he says:
Connect your mic preamp of choice, preferably one that works, and turn on the phantom power.  We’re going to calibrate the drain on the microphone to 11.5 volts.   Take your multimeter and put the red probe on r6. This is right next to the FET.  Take your black probe and put it on the ground hole.  Take a small flat-head screw driver and tweak the pot until you measure 11.5 volts.

I've read using an oscilloscope and injecting a 1K tone into the circuit is the best way to bias the FET, but I don't have an oscilloscope so I was going to do what Schaap did. My questions are:

a) If R6 is the red probe point of contact for the U87, what is the corresponding probe point for the FET847?
b) Would I still be measuring the drain to 11.5v on the FET847?

Thank you in advance for answering my noobie questions. I really did reading this board. There are a lot of smart and interesting people here. I have a serious interest in tinkering with mics and want to learn as much as I can.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 20, 2016, 03:55:13 AM
I was looking for a U49,
but it was out of my budget.

Maybe I should try this one instead :)

Now for capsule and transformer..?
(I'll be looking for flat 1k to 2,5k performance )
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 22, 2016, 03:17:06 PM
Ordered a couple of BM-800.
Will see how they sound stock,
and what to do with them :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 22, 2016, 03:53:09 PM
oh and I just ask Cinemag and the transformer would cost about 59USD
Do you know shipping to Europe/Norway?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 23, 2016, 03:42:05 AM
I guess this one will work in this project:
http://3uaudio.com/cp.asp?id=668
And size/mount/performance-issues I should be aware of?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 23, 2016, 03:47:58 AM
What is a nice budget capsule for this project?
Some U47/49/67 ish
How do I understand  sizes and mount? 25, 34, 35, 50, mm?

Will this circuit work well with a K67 capsule?
Does this one fit, with mount?
http://store.studio939.com/product/35mm-k67-style-capsule

Can I use the stock headbasket, or do I need a HT11a-style?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 23, 2016, 08:29:22 AM
This is a KM84 circuit so you should use a flat capsule. M7,K47,CT12 or similar. Not a capsule with pre-emphasis like 67 or 87 style.  Stock headbasket is fine too but you'll need a capsule mount appropriate for your chosen capsule. Not sure of the best height.

Good luck!
Cheers,
Jonathan
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 25, 2016, 03:55:52 AM
and a microphone parts RK47.
Was this for the BM-800 body?
Did the capsule mount fit well?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 25, 2016, 05:05:26 AM
Guess I'll be going for these capsules (one each):
http://microphone-parts.com/collections/capsules/products/rk47-microphone-capsule
http://microphone-parts.com/collections/capsules/products/rk12-microphone-capsule
and the GZT-47 Transformer
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 25, 2016, 05:08:21 AM
What's this:
Quote
M22 sized hard ring mount for BM800 body
?

Or more precise: What's it for?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 25, 2016, 05:11:24 AM
And btw:
Thanks a lot Dan for making highend and budget-conscious diy-mics available!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on September 25, 2016, 05:20:13 AM
Hi all,
If anyone's interested I have some transformers for these which are the perfect ratio and spec for 847, U47 and for API-312 input transformers.
Get in touch if anyone wants any as only have a few left, if need more I'll have to get some more built.

Regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 29, 2016, 04:20:53 AM
btw: Seeing that the AKG C414 using a c12 capsule.
How close do you think the Fet847 will be with a similar capsule?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 29, 2016, 08:14:56 AM
btw: Seeing that the AKG C414 using a c12 capsule.
How close do you thing the Fet847 will be with a similar capsule?
You can install one and it's going to work well and sound great dependant on the quality of your selected c12 capsule.

I put some ct12's in an m49 circuit and very much like that too.  Not an apple/apple comparison but it is another akg/neumann comparison :)

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 29, 2016, 02:07:30 PM
Also confirmed that this particular PIO does fit when mounted behind the PCB :)

Cheers,
jb

JB,
Is this C8?

Also, if I may ask:

Can I eliminate R2 and C11 if I only do this in cardioid?

Also any thoughts about 1uf in C9 and C10?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 29, 2016, 02:24:47 PM
JB,
Is this C8?

Also, if I may ask:

Can I eliminate R2 and C11 if I only do this in cardioid?

Also any thoughts about 1uf in C9 and C10?

I was referring to using a PIO for C3 - AKA the "output cap" and the one I used fit fine on the back side of the PCB.

R2 & C11 - R2 provides bias voltage to the backplate (~48V) and C11 is final AC shunt so you need both for either card or omni.

C9 & C10 - Those work together with the inductors L1 and L2 to make an RF filter. This is the same setup that is on a U87. Keep those values to prevent RF interference. If you don't want that RF filter in the signal path then just remove all four of those components and install jumper instead of the inductors.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 30, 2016, 04:57:22 PM
Got it. Thanks again, JB!
What kind of PIO cap was that? Is it polarized?


I was referring to using a PIO for C3 - AKA the "output cap" and the one I used fit fine on the back side of the PCB.

R2 & C11 - R2 provides bias voltage to the backplate (~48V) and C11 is final AC shunt so you need both for either card or omni.

C9 & C10 - Those work together with the inductors L1 and L2 to make an RF filter. This is the same setup that is on a U87. Keep those values to prevent RF interference. If you don't want that RF filter in the signal path then just remove all four of those components and install jumper instead of the inductors.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 30, 2016, 05:30:20 PM
If you look in the picture you'll see that it was an "MBM 160V 1.0uF paper/aluminum foil" like this -
http://www.ebay.com/itm/MBM-160V-1-0uF-paper-aluminum-foil-capacitors-Lot-of-20-pc-NOS-/291356624382?hash=item43d63545fe:g:9wAAAOSwzrxUukCn

I preferred the stock BOM cap for that position though. There may be other PIO's that add something desireable.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 30, 2016, 06:42:18 PM
Good to know. Thanks!

Ok, one last question for today (I promise). Looking at the pics that have been posted, I don't see where on the PCB the capsule ground wire is supposed to be soldered... or is that pin above the capsule lead pin the ground or for the rear diaphragm wire?



If you look in the picture you'll see that it was an "MBM 160V 1.0uF paper/aluminum foil" like this -
http://www.ebay.com/itm/MBM-160V-1-0uF-paper-aluminum-foil-capacitors-Lot-of-20-pc-NOS-/291356624382?hash=item43d63545fe:g:9wAAAOSwzrxUukCn

I preferred the stock BOM cap for that position though. There may be other PIO's that add something desireable.

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 30, 2016, 08:38:38 PM
The capsule doesnt have a ground connection. The backplate is connected via the 1g extremely hi z to the filtered and stable 48v supply which provides a DC voltage reference. The front diaphragm connection feeds signal into the fet gate for cardioid and if you want omni just connect the rear diaphragm also into the fet. Those capsule connections are all very hi impedance so any dirt oil or foreign material bridging to ground or other circuit nodes will lead to undesireable noises. Keep it tidy and clean.

Good luck with your build and happy microphoning!
Cheers,
-jonathan
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on October 03, 2016, 08:37:00 AM
Only three of these transformers left for testing out now, if anyone's interested just msg me,

Regards

Spence.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 05, 2016, 01:58:04 PM
Got the mics today
(and pcb. Thanks Dan!)

and I must say: They're quite small.

Checking dimensions for capsule and mount.

I'm not sure the RK-47 with mount will fit.
http://microphone-parts.com/collections/capsules/products/rk47-microphone-capsule
http://microphone-parts.com/products/34mm-capsule-mount
That's 34mm + 22mm = 56mm
That's about the room inside the basket..
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Spencerleehorton on October 05, 2016, 03:09:25 PM
yes, thats why the transformer i've had designed is nice and small and perfect for this build!!!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on October 05, 2016, 04:23:04 PM
Got the mics today
(and pcb. Thanks Dan!)

and I must say: They're quite small.

Checking dimensions for capsule and mount.

I'm not sure the RK-47 with mount will fit.
http://microphone-parts.com/collections/capsules/products/rk47-microphone-capsule
http://microphone-parts.com/products/34mm-capsule-mount
That's 34mm + 22mm = 56mm
That's about the room inside the basket..

I used chunger's type4 headbasket and there was plenty room. I think there was also enough with the stock headbasket on the M7 capsules/mounts. One of my implementation goals on this was for it to be as small as possible for best placement options while still using LDC's.

http://store.studio939.com/product/custom-headbasket-for-c12-clone-microphone

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 05, 2016, 10:17:33 PM
Okay, pardon yet another noob question. What are the 75pf caps for? The ones marked on the BOM description as "Test-Capsule"?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on October 05, 2016, 10:35:52 PM
Okay, pardon yet another noob question. What are the 75pf caps for? The ones marked on the BOM description as "Test-Capsule"?

Hook those up in place of the capsule for testing. The capsule is a capacitor in that range of 70pf or thereabouts. You can then hear the amp under the same circuit conditions as if the capsule were installed yet without the acoustic noise interference. Inject audio or your test tone for biasing / etc...

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 05, 2016, 11:57:18 PM
Hook those up in place of the capsule for testing. The capsule is a capacitor in that range of 70pf or thereabouts. You can then hear the amp under the same circuit conditions as if the capsule were installed yet without the acoustic noise interference. Inject audio or your test tone for biasing / etc...

Cheers!
-jb

Very cool. Thanks JB. If our paths should ever cross, I'm buying the beers.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 06, 2016, 12:08:14 PM
I used chunger's type4 headbasket and there was plenty room. I think there was also enough with the stock headbasket on the M7 capsules/mounts. One of my implementation goals on this was for it to be as small as possible for best placement options while still using LDC's.

http://store.studio939.com/product/custom-headbasket-for-c12-clone-microphone

Cheers!
-jb
Thank you!
Ok, I'll check if I can use stock basket for this one:
http://advancedaudio-europe.com/Mics-Parts-DIY/AK47-Capsule

Hoping to avoid a separate order for headbasket (shipping, vat, fees adds up)
but I guess that's what Dan intended for this project.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: elskardio on October 07, 2016, 08:17:27 AM
80-T350D226K006AT T350D226K006AT Kemet Tantalum Capacitors - Solid Leaded 6.3volts
22uF 10%

C2 (more bass option) 1

Best,
Dan,

Hi guys,
 anyone tried different values for C2 and care to share his results?
Did most of you use 4.7uF ?
Thanks
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on October 07, 2016, 08:44:43 AM
If you want to raise low end use even double of that 10uF or like U87 20uF.
If 4.7uF i recommend 4.7uF MKT Epcos/Siemens if higher Elna Silmic II electolytic or good bipolar.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 10, 2016, 02:28:13 PM
If you want to raise low end use even double of that 10uF or like U87 20uF.
If 4.7uF i recommend 4.7uF MKT Epcos/Siemens if higher Elna Silmic II electolytic or good bipolar.

What are your thoughts about replacing the other Tantalum caps in the circuit?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on October 10, 2016, 02:35:18 PM
All filtering caps you can change for MKT or bipolar (two in parallel instead of one also) without any problem.
Output cap 1uF - of course in the first place ;)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 10, 2016, 08:48:25 PM
All filtering caps you can change for MKT or bipolar (two in parallel instead of one also) without any problem.
Output cap 1uF - of course in the first place ;)

The Elna Silmic  II's have such good reviews all over the web, and they're a lot cheaper. I think I'm going to replace the tants in my BOM with them. Thanks!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on October 11, 2016, 05:02:30 AM
You don't need  Silmics as filtering caps, here something with low esr would be better.
Also, please remember, that most silmics is available to 50V and these are pretty big.
If you have opportunity to replace some with foil caps, then would better.
Usual MKT in uF range cost me similar to silmics, sometimes even cheaper. Bipolar caps usual cheaper.
All depends on location ofcourse.
One thing! Beware fake silmics, buy only from reputable sellers.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 11, 2016, 11:04:07 AM
You don't need  Silmics as filtering caps, here something with low esr would be better.
Also, please remember, that most silmics is available to 50V and these are pretty big.
If you have opportunity to replace some with foil caps, then would better.
Usual MKT in uF range cost me similar to silmics, sometimes even cheaper. Bipolar caps usual cheaper.
All depends on location ofcourse.
One thing! Beware fake silmics, buy only from reputable sellers.

Good to know! There's so much about this circuit I really don't know anything about. So, are the Tants the filtering caps? I was going to order from Mouser to make my life easier. By the way, you wouldn't happen to have a BOM with your best suggested replacements, would you?  :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on October 11, 2016, 06:40:26 PM
No i don't have BOM.
Everything except C1, C2, C3, C9, C10, C11 is for supply filtering.
Try first without C9, C10, L1, L2.
If you don't have problem with RF then good for you.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 12, 2016, 12:16:21 PM
No i don't have BOM.
Everything except C1, C2, C3, C9, C10, C11 is for supply filtering.
Try first without C9, C10, L1, L2.
If you don't have problem with RF then good for you.

Thank you!!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on February 25, 2017, 03:33:35 AM
I've put this project on hold
as the HT11a Sized head basket
is sort of $91  to get here.
Looking for alternative vendors/sellers.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: maq3396 on February 26, 2017, 10:25:53 AM
Hi Dan

Just read this thread...

Sounds like a great microphone for a low price and a fun build.

Will you be doing another run of the pcbs (I didnt see them displayed at the store)?

Thanks
Mac
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on February 26, 2017, 11:24:22 AM
Yes they are still listed and in stock ,
last item on this page,
http://www.vintagemicrophonepcbkit.com/orders.html
Best,
Dan,



Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: maq3396 on February 27, 2017, 02:10:51 PM
OOOps...didnt check the order page!

Thanks Dan

Cheers
Mac
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: tommypiper on February 28, 2017, 12:06:35 PM
What are your thoughts about replacing the other Tantalum caps in the circuit?

My question too.  I've learned to avoid Tants and replace with quality electrolytic, it sounds better.  Tants are usually a carryover from 1960s era supply options AFAIK and modern electrolytic will sound better.  4.7 electrolytic may have been too large in those days to fit inside the mic. 
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Rasta3 on March 01, 2017, 04:02:13 PM
I've put this project on hold
as the HT11a Sized head basket
is sort of $91  to get here.
Looking for alternative vendors/sellers.

Just to share my experience. I had no problem fitting, both ck12 and k47 style capsule either in bm700 and bm800 mics. Enough room for capsule and mount.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: poctop on March 01, 2017, 04:04:14 PM
Just to share my experience. I had no problem fitting, both ck12 and k47 style capsule either in bm700 and bm800 mics. Enough room for capsule and mount.

Cool STuff,
Enjoy ,
Best,
Dan,
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Rasta3 on March 03, 2017, 04:57:39 AM
Yes Dan, cool project.
Now I just need to resolve my last problem in the process.
I asked help in another thread but maybe someone can help me sorting out, here, as well.
What I noticed is that one of the two mics has slightly less high freq than the other, very subtle but I can guess which mic is which just by hearing them.
Just to check I opened up the mics, turned on phantom power and measured the voltage as in the FET biasing, but with the capsule mounted and without the signal injected.
The difference between the two mics is that while the one with more high freq starts at about 8.2V and drops at about 7.8/7.9V  after a couple of seconds, the other mic (the one with less high freq)  starts at about the same 8.2V but continues dropping down the voltage. I waited a couple of minutes and reached 6.8V.
Notice that when I did the scope thingy for the bias, with a virtual scope, the voltage was about 8.2V on both mics, when the clips were simoultaneous.
The answer is, why it is happening this? What coul it be? What can I check? Could it be a problem or should I just live with it? Cause as I said, it makes a very subtle difference, not accentuated.
Thanks for the tips.
Fabio
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on March 03, 2017, 08:22:32 AM
You could graph the frequency response of the circuit to quantify what you are hearing.

Replace capsule with cap. Inject signal. Measure output. Sweep frequency and notate changes in output level. Make a spreadsheet of level and frequency. Graph it.

Compare the two mic's with that test to see how far apart they are.

Swap in a new fet to see if it changes.

Could be another component.

Cheers
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ivansc on March 06, 2017, 02:25:00 PM
Waiting for my pcbs to arrive and really looking forward to getting my feet wet.

Hopefully going to sort out the transformer with Spence in the near future, which will cut down on any more transatlantic waiting time!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on March 06, 2017, 02:56:14 PM
Just to share my experience. I had no problem fitting, both ck12 and k47 style capsule either in bm700 and bm800 mics. Enough room for capsule and mount.
Thank you for sharing!
Where did you buy your capsules?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ivansc on March 08, 2017, 03:36:39 PM
I am about to buy mine from Microphone parts UK - I believe they are actually based in France for europe, unless things have changed in the last few years.

Unless I have the wrong firm I did some translation work for them  for their english language website text a while back.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Rasta3 on March 08, 2017, 06:28:42 PM
You could graph the frequency response of the circuit to quantify what you are hearing.

Replace capsule with cap. Inject signal. Measure output. Sweep frequency and notate changes in output level. Make a spreadsheet of level and frequency. Graph it.

Compare the two mic's with that test to see how far apart they are.

Swap in a new fet to see if it changes.

Could be another component.

Cheers
-jb

Thanks for the tips, I'll try to figure it out.

Thank you for sharing!
Where did you buy your capsules?

I bought them from capsule groupbuy, here from this forum.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on March 11, 2017, 04:08:50 AM

I bought them from capsule groupbuy, here from this forum.
Ok thanks! Maybe I should try to get hold of one of those then.
I checked with microphone-parts and the mount there was to big for this body.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Carnesd on March 16, 2017, 02:22:22 PM
Does any body have the Schematic and BOM files they could send me,  went to build this mic yesterday and looks like Dany's dropbox is down and not sure when it will come back up.  I'd like to get building tonight if possible.   Thanks in advance :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on March 16, 2017, 03:24:33 PM
Here is a ZIP with the original documentation - BOM, Schematics, and some PDF's on the Cinemag transformer for BV7 replacement. Project notes.

I'm sure Dany's links will back up soon.

Cheers and good luck with the mic(s)!
-jb

*** HINT ***
Change file attachment extension from .PNG to .ZIP when you download.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Carnesd on March 16, 2017, 05:20:25 PM
Here is a ZIP with the original documentation - BOM, Schematics, and some PDF's on the Cinemag transformer for BV7 replacement. Project notes.

I'm sure Dany's links will back up soon.

Cheers and good luck with the mic(s)!
-jb

*** HINT ***
Change file attachment extension from .PNG to .ZIP when you download.

Sweet exactly what I needed,  guess I need to learn to download any project info before hand.  Cant wait to see how this thing sounds, Thanks again!
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ivansc on March 17, 2017, 08:14:05 AM
Ok thanks! Maybe I should try to get hold of one of those then.
I checked with microphone-parts and the mount there was to big for this body.

What did you wind up doing for a capsule? I found the 3-d print project for a mount on here but am still dithering over what capsule/mount to buy. Definitely going with something like an RK47 but, as is the way of these things, there seem to be a lot of choices...
Good news is my Mouser order arrived early and is complete so the soldering iron will be out later.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ivansc on March 17, 2017, 01:37:04 PM
Wow such a quick build! Just wish I had bought a decent pair of side cutters - min are dead. And my fine soldering skills....!!!!

Transformer I ordered turned out to be too big  & still scratching my head over the capsule....

One thing: middle leg of the FET seems to be going overland on most of your builds.  Not a problem for me, but  if I DO decide to connect on the underside, are there any issues with interference or other pickup involved I should know about?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Delta Sigma on March 17, 2017, 09:08:16 PM
Wow such a quick build! Just wish I had bought a decent pair of side cutters - min are dead.....

I love these cutters for trimming component leads: http://ca.mouser.com/ProductDetail/Apex-Tool-Group/MS545JV/?qs=sGAEpiMZZMuxaxGVT3gSIqaVf4WVTCQhaxnQ7q4aclc%3d (http://ca.mouser.com/ProductDetail/Apex-Tool-Group/MS545JV/?qs=sGAEpiMZZMuxaxGVT3gSIqaVf4WVTCQhaxnQ7q4aclc%3d)

I use very nice Snap-on flush cuts at work but for PCBs and other component trimming at home I prefer the smaller semi-flush Xcelites. I also have the tapered ones but use them less, mostly on PCBs.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 01, 2017, 09:52:30 AM
Starting my build now.

A few questions:
- c2;c3;c6;c4 is marked polarized. But the tantalum caps are non-polarized, right?
- C2: Less bass, is 4,7uf for flat response?
- "The Silk Screen contains 1 Errata the P+ , P- and S+ , S- are Inverted but the Picture shown in this thread shows the proper position":
 My pcb seems exactly like the picture. Does that mean this is fixed on my revision?
- Hi-z-nodes for back and front capsule are insulated. I'm using cardioid only.
How are these connecting to the rest of the pcb?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: useme2305 on July 01, 2017, 11:18:25 AM
Starting my build now.

A few questions:
- c1;c2;c3 is marked polarized. But the tantalum caps are non-polarized, right?

 tantalums are polarized
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 01, 2017, 01:50:36 PM
tantalums are polarized
Oups... thanks! Hope I was lucky. Why equal legs then?
Need to get my magnifier ready for that microscopic print.

Edit: 3/4 right, that's luck. Me and desoldering are not good friends.
But, managed to get the last one in right as well  :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 01, 2017, 02:51:37 PM
There must be something I don't understand about R1; R2 and C1 and their connection to FO-turret.
I see different pictures connecting in different ways.
And is Q1 to be manually connected as well?

I see I jumped in soldering, before understanding this too well..
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 02, 2017, 07:46:45 AM
The capsule doesnt have a ground connection. The backplate is connected via the 1g extremely hi z to the filtered and stable 48v supply which provides a DC voltage reference. The front diaphragm connection feeds signal into the fet gate for cardioid and if you want omni just connect the rear diaphragm also into the fet. Those capsule connections are all very hi impedance so any dirt oil or foreign material bridging to ground or other circuit nodes will lead to undesireable noises. Keep it tidy and clean.
Ok, I connect back capsule to turret Bck? And then, nothing further?
And front to FO turret, the FO turret to C1, R1 and Q1G?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 02, 2017, 10:14:15 AM
Ok, so I just follow poctops schematic:
FO to C1; R1 and Q1G
Bck to C11 and R2
this is for cardioid.
Using some wire or leftovers

Then if I would like omni:
Bck to Q1G ??

Capsule ground to Glink?
(My capsule came with aground wire)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 04, 2017, 09:17:06 AM
Is this right?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Vac11 on July 04, 2017, 01:58:12 PM
Sorry, but this is not right... You have to make a floating conection from the other side of PCB.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 06:14:43 AM
Thank you for answering  Vac11,
but I don't understand.

Is it C1 to FD you mean? Why would making the connection floating from the other side make any difference?
As is, I've connected C1 to FD on the back.
Together with the connections:
FO to C1; R1 and Q1G
Bck to C11 and R2
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Vac11 on July 05, 2017, 06:37:58 AM
https://groupdiy.com/index.php?topic=63691.msg827963#msg827963

There is proper connection on the photo in linked thread ...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 06:50:45 AM
https://groupdiy.com/index.php?topic=63691.msg827963#msg827963

There is proper connection on the photo in linked thread ...
Thanks a lot!

Ok,
FD to C1; R1 and capsule front (not to fet gate? I see a connection going down there as well, don't I?)
Bck to R2 and capsule back, (not C11? or is C11 soldered to that R2-Bck-connection?)
?

(The pictures shows 2 mics, I'm not sure how identical they are)

When inspecting the picture, it seems quite identical to what I've done.
Or, what is the difference?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 07:09:36 AM
Here's the markings for back
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Vac11 on July 05, 2017, 07:12:13 AM
The second leg of the R1, R2, C11, C1 you have to solder direct to teflon PIN...from your pic it looks like you solder those to the PCB and then to teflon PIN...that is wrong.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 07:29:26 AM
The second leg of the R1, R2, C11, C1 you have to solder direct to teflon PIN...from your pic it looks like you solder those to the PCB and then to teflon PIN...that is wrong.
Thanks, but I have soldered them to the teflon pins.
Oh, you mean it's an error using the pcb? Well, the ones I've used are meant for this, and not connected to anything else, right?
So, it's more a matter of convenience?
(Thanks for the drawing btw.)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Vac11 on July 05, 2017, 09:33:32 AM
Try this...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 10:05:19 AM
Try this...
Thanks a lot!
Yet, I still don't understand any electronic difference in the two ways.

Anyway, I'll be waiting some more weeks for some capsule-mount screws to arrive.
So, should be time enough to get this right :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on July 05, 2017, 10:53:03 AM
Hi G-Sun, I saw a flurry of activity here regarding this project so I wanted to comment on what many refer to as "the high impedance nodes" or similar....

These following junctions or nodes are all considered extremely high impedance. In this case this means that surface conductivity on the circuit board is likely even less resistance (eg; 1Gohm) than the values in the circuit. In other words current flow takes a shortcut and makes noise spurts / fizzles / frying-sounds etc... Any dust or oils from your hand can contaminate this hi-z area in the circuit and lead to noisy audio.... This is why all of these nodes are connected in the air and not on a circuit board (air is the best insulator). The teflon standoff's are extremely hi-z tolerant so they provide a solder point and electrical path between front and back of PCB for connectivity. This is why we also use alcohol on cleaning swabs or acid brushes to remove any finger oils / etc on the hi-z points.

- Connection or node between FET gate/input and capsule front diaphragm.
- Connection or node between R1 (1G) and capsule front diaphragm
- Connection or node between C1 and FET gate/input.
- Connection or node between capsule backplate and C11.
- Connection between R2 (1G) and backplate (this is the 48V line providing capsule voltage)

If you solder these nodes on the PCB it may well work for now but it will become more and more susceptible to noise over time and may even have noise issues right out of the gate...

In condenser microphones the capsule connections are always very hi-z and are typically either floating in the air or connected to a teflon standoff which is also very hi-z. The electrical difference between the two connection methods is that the one where the hi-z nodes are connected to the PCB instead of floating can and do suffer from short circuit over PCB surface resistance...

One way to illustrate this is to measure the resistance of your body by holding your meter probes in a hand and measuring resistance- what is it measure?? 3 or 4M or so? That's way less than 1G... Just a point of reference regarding contamination from finger oils and dust or similar...

Cheers!
-jonathan


Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on July 05, 2017, 02:53:26 PM
Thanks a lot Jonathan!
Now things get clearer for me.
Sorry Vac11 for not understanding the difference in your method compared to what I did.
This was a part of electronic design that was outside my radar,
hence my mistakes.
Now, I just need to see how to best correct this.

So, Fet-gate, Q1G, should have the middle leg bent to air for this to be done right?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Vac11 on July 05, 2017, 03:11:14 PM
So, Fet-gate, Q1G, should have the middle leg bent to air for this to be done right?

Correct...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Ampampam on July 06, 2017, 12:16:25 PM
Can anyone tell me why did they choose an RF unit for microphone amplification? What should be explanation? I just can not understand it.   ??? Thank you!

Regards
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: zaraxisof on August 08, 2017, 01:57:35 PM
Hey Everybody!
Long time lurker. First time poster. I'm seriously contemplating building this FET847 as my first Poctop board mic.

I have a question about biasing the FET. In the thread starter Poctop said:
So in Andrew Shaap's build (http://www.vintagemicrophonepcbkit.com/Neumann%20U87%20Build.htm), he says:
Connect your mic preamp of choice, preferably one that works, and turn on the phantom power.  We’re going to calibrate the drain on the microphone to 11.5 volts.   Take your multimeter and put the red probe on r6. This is right next to the FET.  Take your black probe and put it on the ground hole.  Take a small flat-head screw driver and tweak the pot until you measure 11.5 volts.

I've read using an oscilloscope and injecting a 1K tone into the circuit is the best way to bias the FET, but I don't have an oscilloscope so I was going to do what Schaap did. My questions are:

a) If R6 is the red probe point of contact for the U87, what is the corresponding probe point for the FET847?
b) Would I still be measuring the drain to 11.5v on the FET847?

Thank you in advance for answering my noobie questions. I really did reading this board. There are a lot of smart and interesting people here. I have a serious interest in tinkering with mics and want to learn as much as I can.

Any reply to this? I am interested in building this as i have some BM 800 unused bodies.
I have the same questions as Wordsushi and would appreciate if have some help  here. I talked with Wordsushi and he aslo waits for a reply.

Thanks in advance.  :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: TillM on August 08, 2017, 05:24:54 PM
Look at the picture to see how you can bias the mic with a DMM.
Same method with a oscilloscope like on the u87.

Note: it doesn't matter if you change the red and black probe, if you change them your multimeter measure "- Volts".
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on August 08, 2017, 09:39:34 PM
Look at the picture to see how you can bias the mic with a DMM.
Same method with a oscilloscope like on the u87.

Note: it doesn't matter if you change the red and black probe, if you change them your multimeter measure "- Volts".

Awesome. Thank you for that. Much appreciated!
Am I still trying to adjust to 11.5v like with the 87?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: TillM on August 09, 2017, 07:45:43 AM
Look at the original schematic.
It shows 10v at the drain.
So I think with DMM Method 11,5v should be a good starting point.
Biassing with scope is always a better method, but you can use your DMM.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: zaraxisof on August 09, 2017, 12:58:06 PM
Look at the original schematic.
It shows 10v at the drain.
So I think with DMM Method 11,5v should be a good starting point.
Biassing with scope is always a better method, but you can use your DMM.
Thank you TillM! :)  Adjusting to 10v for better and accurate results maybe?
I have seen also a method described in U87 built, without oscilo, inserting 1k sine wave from daw, but didnt understand clearly.
If you dont mind, could you please explain it in details? Where do i have to inject signal,how the connections will be done?I have to listen to it with hadphones? etc...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on August 09, 2017, 01:15:43 PM
Think of adjusting this voltage as an offset bias such that when signal clips it clips symmetrically on the positive and negative waveforms inside the FET.

It depends on the specs of that particular FET. 11.5VDC or 10VDC is only a little arbitrary but when the FET is selected such that 11.5V or 10V or whatever is on their original schematic presents symmetrical clipping then the selected FET will have the intended and desirable attributes regarding symmetry, operating points, headroom, and SNR / distortion, etc...

The FET input is the gate leg. The FET output is the drain leg. Measure that voltage on the source leg and adjust source pot for symmetrical clipping.

In addition to the audio (AC signal) on the drain leg there is also about 22VDC on the drain leg to power the FET. You can tap after the output cap to get just the AC or audio part of the signal into your measuring device.

Cut the end off an XLR and use the pin1 wire for GND and pin2 wire as input to your DAW... Then use either a software scope or just record the audio and adjust/measure.

Apply signal to the FET gate leg (and disconnect the capsule during these tests)... Adjust gain such that you can gain the signal up and as clipping starts it is symmetrical

Adjust the source resistor up/down and increase/decrease gain of the signal into the FET until you can get symmetrical clipping at the fet.

Since this is simply measuring and setting the operation of the FET it is advised to disconnect capsule and trafo to reduce interference.

****
On this FET847 there is a spot to install a precision source resistor and once you have your FET biased correctly you can measure and order that part or just use the pot.

Ciao!
-johann
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 11, 2017, 02:24:54 AM
Are you sure that's the case for the bolded node?

At least to my (admittedly feeble) mind, that would be the case, if the input circuitry looked more like it does in the case of SDC's (KM84, Schoeps etc), where you're forced to have the capsule connected with one end (the backplate) to the grounded case / body, and the other end, through a coupling cap, to the JFET gate.

The arrangement used here reminds me of the "ChinaMicMod" schematic of Zapnspark from the Yahoo micbuilders group, where you actually get to remove one of the 1G resistors (R2, in this case) and the input coupling cap, by applying the bias voltage to the backplate - just like here.

And besides, 1G + 100nF gives you a 100-second RC constant, which means the capsule bias voltage will only reach its maximum in about five times as long (over 6 minutes) ;)

Hi G-Sun, I saw a flurry of activity here regarding this project so I wanted to comment on what many refer to as "the high impedance nodes" or similar....
<snip>

- Connection or node between FET gate/input and capsule front diaphragm.
- Connection or node between R1 (1G) and capsule front diaphragm
- Connection or node between C1 and FET gate/input.
- Connection or node between capsule backplate and C11.
- Connection between R2 (1G) and backplate (this is the 48V line providing capsule voltage)


On a side-note, on my BM800 / sE2200A "retrofit" boards, i "guilded the lily" and also inserted a "mask stop" polygon on the top & bottom of the board, in the hi-Z area, to not have the soldermask cover, "just in case" ;D Not to mention, striving to minimize connection distances, and not have a spaghetti of traces all over the place...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 11, 2017, 06:16:41 AM
"Just for kicks", and after some PM's between myself and zaraxisof, i took the liberty of putting my own spin on the circuit (re-drew the schematic so that it was clearer and made more sense - to me, at least), and whipped together a quick board design. I'll gladly receive comments / critique on it ;)

The thick-hashed areas at the top & sides are soldermask-stop areas. And whaddya know, all the connections fit on a single copper layer, AND with no jumpers ;D

I'm not 100% sure the positions of the two mounting holes on the sides are totally accurate, i just eyeball-ballpark'ed them. And couldn't be bothered to unpack one of my BM800's and measure... :P

<Edits = updated the screenshot a couple times>
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: zaraxisof on August 11, 2017, 09:56:55 AM
It seems like a more "maked up" and "well dressed" lady now... :) :p
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: WrmZ on August 11, 2017, 10:16:07 AM
Hi,

I build fet847 mic from schematics and it sounds wonderfull but i got one problem - it there an option to increase the gain of this mic?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 11, 2017, 10:19:12 AM
Probably not without adding some oscillator to boost the capsule bias voltage.

PS: What voltage are you getting at the common point between the two 2.2k resistors?


Hi,

I build fet847 mic from schematics and it sounds wonderfull but i got one problem - it there an option to increase the gain of this mic?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on August 11, 2017, 10:30:34 AM
This is a single FET driving a transformer. It's not going to have a huge output voltage. This is essentially the same as a U87 without the de-emphasis which is also noted for "low output".

Consider that this might be  a desirable quality in some regards because for one thing less gain in the mic causes you to use more gain in your pre-amp which often is achieved by reducing negative feedback and thus simply makes the signal "more better" or my other favorite technical term "Magic-Microphone".

A PCB jumperable (or switchable) capacitive pad could be useful if you have a set of these mic's dedicated for close mic drum recording... But you could also simply solder it in place and dedicate those mic's for close mic drum duties...

Cheers!
-johann
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on August 11, 2017, 11:56:29 AM
Are you sure that's the case for the bolded node?

--------
- Connection or node between capsule backplate and C11.
- Connection between R2 (1G) and backplate (this is the 48V line providing capsule voltage)
--------


The backplate, R2 (1G), and C11 all connect to form a node. This is hi-z node for DC signals and low Z for AC signals and should be floating or terminated at a teflon standoff terminal.



And besides, 1G + 100nF gives you a 100-second RC constant, which means the capsule bias voltage will only reach its maximum in about five times as long (over 6 minutes) ;)
Hmmm... Ok. If the capsule bias is reduced =by half then we lose 6db of signal. When it's @ 48VDC then bringing it up to a "prescribed" 60VDC will provide better signal to noise ratio but not a full 6db more. This is true and 60V is what we use standard in many other mic's. Vintage U87 uses this "48V" method so we know it's a solution that worked fine during that particular run of the mic.


----
I recommend for DIY'ers to experiment with variable capsule voltage by temp modifying a tube mic using variable rear capsule voltage as the pattern select - discnect capsule front into the grid so that it's only using the rear diaphragm then adjust your pattern to increase/decrease bias voltage and see how that changes the sound... COmpare 48V, 60V, 30V, etc...
----

Not sure I understand what you did with re-working the PCB but that's great if it works. This circuit is a simple basic building block which has certainly been implemented in other mic's. The original design goal with this implementation was to make a known good high quality build available with a minimum of extra features and a BOM order from one vendor for components other than capsule, transformer, body.

A KM84 modified for LDC use with the idea that more of them in your locker is just better and you can throw one on just about anything...

You can do a lot from this starting point to modify for your needs. Did you say your PCB is single layer single sided? Will you upload the gerbers and masks so full on DIY'ers can self etch drill and modify further if desired?

Cheers and good luck to all!
-jb

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 11, 2017, 12:25:08 PM
Just to try to make my point of view as clear as i can, i've attached a schematic with the two variants of input circuitry.

In SDC's, mechanics / physical constraints force the construction of the capsule to have one side of it inevitably connected to ground (see the left side, as in the KM84, Schoeps, MXL603, whatever other non-electret SDC's you can think of).

So in that case, there's nothing that can be done to change the topology.

Now, many of the cheap chinese LDC's use the same Schoeps circuit, BUT in LDC's we're NOT forced to have one side of the capsule unavoidably connected to ground.  I can't be 1000000% sure about it, but this, as well as the desire to skip over the input coupling (or DC blocking) cap, is likely what inspired Zapnspark to come up with his "ChinaMicMod" alteration.

I'm not sure whether it's moral or ethical to upload / publish his actual schematic of the thing here, but it's definitely over on the micbuilders Yahoo group. But i've redrawn the essentials on the right side of the attached screenshot.

Now, power supplies are pretty much universally low-impedance sources, correct? So how and why would the  R2/C11 node (need to) be a high-impedance one? This is on the "back" side of the capsule, which is, in essence, a capacitor itself.

In the SDC version, with one side of the capsule to the ground, the other side, of course, needs a bias voltage across it (since the signal voltage is produced from the varying capacitance of the capsule, and without a bias voltage to modulate, you would get no signal). That then gets coupled through C3 (which also blocks the high bias voltage from "toasting" the JFET) in my schematic here, over to the gate.

But in the LDC version, since we have both sides of the capsule "free", we can apply the bias voltage (which "should" come from and be, a relatively low-impedance source) to the backplate, and use the capsule itself (which is a capacitor, remember?) AS the input DC-blocking capacitor.

It's worthy to note, though, that between the two variants of this input topology, the phase is reversed (since the bias voltage is applied to the other side of the capsule).

Is any of this making any sense whatsoever? ;D

Regarding the time constant, i never mentioned anything about 48v, or 60v, or any absolute value of the bias voltage. All i was saying was, if you read more carefully, that with that 1G / 100nF filter, it would take something in the region of 500 seconds (SIX minutes) for the capsule bias voltage to reach whatever final / maximum voltage it can.

You DO know what the RC constant is, right? http://www.referencedesigner.com/rfcal/cal_05.php
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: WrmZ on August 11, 2017, 12:36:40 PM
thx,

the case was about "warming up" mic and waiting for raising capsule voltage - in first test i was recording just after enabling phantom voltage   wchich resulted in low gain.

I was not aware of such high value of RC contant - thanks again for clarifying this

I did my clone on veroboard, so i don't need pcb design.

One more question about C1 - if i understand it correctly it makes negative feedback - when value of this cap is lower it should give me slightly more gain and bass - it is right?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 11, 2017, 12:39:50 PM
Henry Spragens did a pretty nice write-up on the KM84 circuit over on his blog:

http://audioimprov.com/AudioImprov/Mics/Entries/2015/4/23_Basic_FET_Microphone_Circuits.html

Scroll down to the second (coloured) schematic ;)

One more question about C1 - if i understand it correctly it makes negative feedback - when value of this cap is lower it should give me slightly more gain and bass - it is right?

And thanks for confirming my hunch ;)

the case was about "warming up" mic and waiting for raising capsule voltage - in first test i was recording just after enabling phantom voltage   wchich resulted in low gain.

I was not aware of such high value of RC contant - thanks again for clarifying this
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 12, 2017, 07:14:14 PM
I'll attach the gerbers one of these days, after i "polish" the component silkscreen and export the files, but at least for now, here's my suggestion of a Mouser BOM, with more... shall we say, "down to earth" component choices?  ::)

1.48eu for each (!!!) of the two temporary testing capsule-replacement capacitors; same for each of the two output filter inductors- are you friggin' kidding me???  :o

Ok, deep breath, calming down....

Code: [Select]
jumper 571-1-881545-4 1pc
3-pin header   710-61300311121 1pc
68p test-capsule        810-FG18C0G1H680JNT0    2pcs
2.2k 1%    603-MFR-25FBF52-2K21    10-20pcs, hand-match
SPDT switch    642-TL36W000000     1pc
100n film caps       505-MKS2D031001A00MC    3pcs
1u output cap       505-MKS2C041001FMSSD    1pc
4.7u source cap     647-ULD1H4R7MDD1TD     1pc (option, less bass)
10u caps     667-ECA-1HM100I     2-3pcs
22u cap     667-ECA-1VM220B     1pc (option, more bass; could be used to replace C4 & C6 too)
47k resistors     603-MFR-25FBF52-47K5    2pcs (replacing the 56k R6)
10k 603-MFR-25FBF52-10K     1pc
4.7p C0G feedback       810-FG18C0G2A4R7CNT6    1pc (option)
4p mica feedback 598-CD15CD040DO3F     1pc (option)
10M resistors     279-CFR25J10M     3pc (replacing the 1G R2)
25k trimmer     858-67WR25KLF 1pc
JFET 610-2N3819 1pc
pin turret     534-11218 1pc
1n caps      505-FKS2D011001AKC00    2pcs (replacing the 330p ones)
47u inductors     542-78F470-RC      2pcs
1G resistor      279-RGP0207CHK1G0     1pc (1G R2 unnecessary)
24v zener     512-1N5252BTR 1pc
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: zaraxisof on August 12, 2017, 07:25:21 PM
 ;)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: zaraxisof on August 13, 2017, 01:06:35 PM
I'll attach the gerbers one of these days, after i "polish" the component silkscreen and export the files, but at least for now, here's my suggestion of a Mouser BOM, with more... shall we say, "down to earth" component choices?  ::)

1.48eu for each (!!!) of the two temporary testing capsule-replacement capacitors; same for each of the two output filter inductors- are you friggin' kidding me???  :o

Ok, deep breath, calming down....

Code: [Select]
jumper 571-1-881545-4 1pc
3-pin header   710-61300311121 1pc
68p test-capsule        810-FG18C0G1H680JNT0    2pcs
2.2k 1%    603-MFR-25FBF52-2K21    10-20pcs, hand-match
SPDT switch    642-TL36W000000     1pc
100n film caps       505-MKS2D031001A00MC    3pcs
1u output cap       505-MKS2C041001FMSSD    1pc
4.7u source cap     647-ULD1H4R7MDD1TD     1pc (option, less bass)
10u caps     667-ECA-1HM100I     2-3pcs
22u cap     667-ECA-1VM220B     1pc (option, more bass; could be used to replace C4 & C6 too)
47k resistors     603-MFR-25FBF52-47K5    2pcs (replacing the 56k R6)
10k 603-MFR-25FBF52-10K     1pc
4.7p C0G feedback       810-FG18C0G2A4R7CNT6    1pc (option)
4p mica feedback 598-CD15CD040DO3F     1pc (option)
10M resistors     279-CFR25J10M     3pc (replacing the 1G R2)
25k trimmer     858-67WR25KLF 1pc
JFET 610-2N3819 1pc
pin turret     534-11218 1pc
1n caps      505-FKS2D011001AKC00    2pcs (replacing the 330p ones)
47u inductors     542-78F470-RC      2pcs
1G resistor      279-RGP0207CHK1G0     1pc (1G R2 unnecessary)
24v zener     512-1N5252BTR 1pc

Added all costs down and its about 10-12 euros, depends on some personal choices and options !!
Amazing kudos khron :) :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 14, 2017, 06:22:43 AM
I think i'm pretty much done with making the board "pretty". And by "board" i mean "silkscreen" - surely the part values are enough, and component designations aren't necessary (R2, C6 etc), right?

For the record, the board doesn't even need to have that tapered shape; my BM800 boards aren't, and they fit just fine. The only catch is to not have any component leads too close to the outside edges of the board (so they don't clash with the chassis beams).

Which Gerber layers / files are required? So i know which ones to export...

Did you say your PCB is single layer single sided? Will you upload the gerbers and masks so full on DIY'ers can self etch drill and modify further if desired?

-jb

[Later edit, re: component value alterations]

With 3x 10M and 3x 100nF filtering for the capsule bias voltage, it should reach its maximum in around "only" 45sec or so ;)

The difference between R6 being 56k vs. 47k is literally minimal. I simulated a worst-case load in LTspice - a 48v source, with 4.5kohm series resistance (the 2x 6.8k in parallel inside the preamp, in series with the 2x 2.2k in the mic), and a 57k load (the 47k drain resistor plus the 10k R5 that's part of the power-filtering, a zero source resistor and the JFET being a dead short).

Stock current draw is 408uA, and 462uA with 47k. Voltage across the zener diode (ie. before R5 in the schematic) is 23.28v stock vs. 24.2 with 47k. Current through the load is 408uA stock (likely because the voltage is lower than the 24v of the zener, so it's NOT actually doing any regulating; seems to act more like a voltage clamp / limiter) vs. 424uA with 47k.

[Yet another edit, this time on the PCB]

I noticed / remembered the length (longest dimension) of the board was 52mm or so, so i moved the top half a couple ticks lower, to fit it within (ie. ever so slightly under) 50mm. Board manufacturers usually have different prices for "up to 5x5cm boards" versus "up to 5x10cm boards" ;) Just a(nother) little cost-saving measure, with the side-effect of getting an even more compact board, and as such, shorter signal trace lengths ;D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 14, 2017, 08:26:13 PM
The backplate, R2 (1G), and C11 all connect to form a node. This is hi-z node for DC signals and low Z for AC signals and should be floating or terminated at a teflon standoff terminal.

While taking a look around, i came across the D-U87 thread, and i was quite surprised to see this:

https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a02187.jpg

I don't see any teflon stand-offs for those 1G resistors, soooo... What's the deal there? :P 1G resistors, but no high-impedance nodes to worry about?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on August 15, 2017, 05:11:42 AM
While taking a look around, i came across the D-U87 thread, and i was quite surprised to see this:

https://io.groupdiy.com/file/gdiy-2017/u/39511/58d1402a02187.jpg

I don't see any teflon stand-offs for those 1G resistors, soooo... What's the deal there? :P 1G resistors, but no high-impedance nodes to worry about?

Some mikes don't have it - works without problem, some have just teflon isolator (like for transistor heatsink mount), and some have (very clever) just legs in the air (gate and resistor + capsule wire).
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: wlinart on August 15, 2017, 05:48:22 AM
Which Gerber layers / files are required? So i know which ones to export...

... (snip)

I noticed / remembered the length (longest dimension) of the board was 52mm or so, so i moved the top half a couple ticks lower, to fit it within (ie. ever so slightly under) 50mm. Board manufacturers usually have different prices for "up to 5x5cm boards" versus "up to 5x10cm boards" ;) Just a(nother) little cost-saving measure, with the side-effect of getting an even more compact board, and as such, shorter signal trace lengths ;D

I think that we need the full zip file of the gerbers for using with board manufacturers.
For self-etching i thnik the bottom layer would be sufficient, but others with more experience could help better with that aspect.
tip: to upload gerbers on this site you would need to change the extension, to for example .pdf or .png in stead of .zip

Thanks for doing this  :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 15, 2017, 08:48:54 AM
"Of course" i'd put them all in a zip file - i'd have to be almost insane to attach each file to a separate post ;D

Yes, that limitation's quite annoying, but good thing there are ways to "bend" that rule...

Well, since mine's a single-layer board, i'm guessing (in a physical order):
- bottom soldermask
- bottom copper
- top soldermask(?)
- top silkscreen (component values only, no designators, ie. R3, C6 etc, to not overcrowd the board - it's full of components ;) )

I think that we need the full zip file of the gerbers for using with board manufacturers.
For self-etching i thnik the bottom layer would be sufficient, but others with more experience could help better with that aspect.
tip: to upload gerbers on this site you would need to change the extension, to for example .pdf or .png in stead of .zip

Thanks for doing this  :)

And no real thanks needed - this project was recently brought (back) to my attention, and when i took a closer look at the board, i took it as a challenge to considerably improve the layout :)

Some might argue i am challenged, but... that's a story for another time ;D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: wlinart on August 24, 2017, 07:54:01 AM
"Of course" i'd put them all in a zip file - i'd have to be almost insane to attach each file to a separate post ;D

Yes, that limitation's quite annoying, but good thing there are ways to "bend" that rule...

Well, since mine's a single-layer board, i'm guessing (in a physical order):
- bottom soldermask
- bottom copper
- top soldermask(?)
- top silkscreen (component values only, no designators, ie. R3, C6 etc, to not overcrowd the board - it's full of components ;) )

What i actually meant to write was: I think that for using a manufacturer of pcb's, like you suggested, we would need the full gerbers, with all the layers. But of course i could be wrong about that.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 24, 2017, 08:21:08 AM
As far as i know, and depending on what boards you order (single or double sided), manufacturers only use / apply the layers you provide them. Some even have options for silkscreen on one side only, or both sides (which may or may not cost extra), etc.

That's why i gave that example of a layer list :)

For the record, Eagle (the CAD i use) has dozens of layers one can use, but i doubt that's necessary in this case ;D

What i actually meant to write was: I think that for using a manufacturer of pcb's, like you suggested, we would need the full gerbers, with all the layers. But of course i could be wrong about that.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: wlinart on August 24, 2017, 10:43:02 AM
In that case, forget what i said  ;D
 :-[
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on August 24, 2017, 11:00:22 AM
No worries, we all gotta learn somehow ;) "At least" this isn't even close to "the hard way" ;D
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on September 12, 2017, 04:41:37 AM
I have a GZT-47 transformer
and the BM800 body

If both sides of the metal in the transformer connects with the body of the mic,
will that affect performance?

edit: I'll add some el.tape there.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 27, 2017, 02:05:52 PM
Just curious... Has anyone tried to build one of these with a flat-response (or flatter response, actually) K67 style capsule like Chungers 35mm K67 or 3u Audio's flat K67?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 28, 2017, 10:32:26 AM
The K67 style capsules should have a pre-emphasis or "peaked high frequency" response. The U87 and U67 circuits are designed to "de-emphasize" that response and bring the capsule signal back towards "flat" while at the same time reducing HF noise. This KM84 circuit is flat with no de-emphasis so best suited for so-called "flat capsules" like C12, K47, M7 or even maybe a sony C37 style capsule if you were lucky enough to get any of those when Dale was making them.

If you use a K67 style capsule with the built-in pre-emphasis then it will seem bright and spitty but they all sound different right and you can also always EQ it too :)

Cheers!
-jb
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on September 28, 2017, 04:04:14 PM
The K67 style capsules should have a pre-emphasis or "peaked high frequency" response. The U87 and U67 circuits are designed to "de-emphasize" that response and bring the capsule signal back towards "flat" while at the same time reducing HF noise. This KM84 circuit is flat with no de-emphasis so best suited for so-called "flat capsules" like C12, K47, M7 or even maybe a sony C37 style capsule if you were lucky enough to get any of those when Dale was making them.

If you use a K67 style capsule with the built-in pre-emphasis then it will seem bright and spitty but they all sound different right and you can also always EQ it too :)

Cheers!
-jb

Yeah, Chunger said his 35mm works nice in flat circuits and I know Guosheng has said the capsule in his GZ67 is for a flat circuit too so I figured I'd ask if anyone had tried one in here just for laughs. 
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: RuudNL on September 29, 2017, 03:18:06 AM
A fact is that a K67 capsule has a certain HF boost. But there are a lot of differences.
The amount of boost varies from manufacturer to manufacturer.
Most Chinese microphone manufacturers use K67-style capsules together with a 'flat' amplifier circuit, resulting in an overbright microphone. But maybe you will even like this...
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on September 29, 2017, 10:22:00 AM
Didn't tested both "flat" options - but this could be possible. I found at least two chinese k67, which weren't not so hyped in highs.
Sometimes also polarisation voltage apllied to diaphragm (not the backplate) helps a little (depends on many factors, always worth to try).  Try one of these "flat" capsules and you will see - always you can try DC on diaphragm as also cap to ground for hf smoothing.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: 0dbfs on September 29, 2017, 10:49:33 AM
Yeah. CHeck out the U87 schematic and look at the signal path from top of FET (output) to C9 -to-  R8 and C6 (in parallel) which then feeds to the backplate... This is the negative feedback de-emphasis part of that circuit.

IOW -
The signal coming out of the FET is fed through an eq / filter (R8 and C6) which then causes modulation on the backplate. This modulation signal is band limited due to the filter and since it's on the backplate it is opposite in polarity and therefore subtracts from the signal produced on the front diaphragm and fed into the FET... Essentially a notch filter. I don't know the exact math but you can probably google that for more specifics on the filter frequencies / etc...

Otherwise the U87 and KM84 circuits are pretty much the same with a slightly different transformer ratio and of course the pattern option differences.

You could put a BV08 in this mic and a K47 or M7 if it would fit and it's basically a "Single FET U47" (not a FET47)... I wonder if we could parallel a couple FET's similar to how the ||6028 implementation works - reducing output Z and increasing drive capability of the active device.. I might experiment with that a little but the mic body in this thread would probably be too small for the BV08 :)

Cheers!
-j
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: ln76d on September 29, 2017, 10:52:44 AM
Yeah. CHeck out the U87 schematic and look at the signal path from top of FET (output) to C9 -to-  R8 and C6 (in parallel) which then feeds to the backplate... This is the negative feedback de-emphasis part of that circuit.

IOW -
The signal coming out of the FET is fed through an eq / filter (R8 and C6) which then causes modulation on the backplate. This modulation signal is band limited due to the filter and since it's on the backplate it is opposite in polarity and therefore subtracts from the signal produced on the front diaphragm and fed into the FET... Essentially a notch filter. I don't know the exact math but you can probably google that for more specifics on the filter frequencies / etc...

Otherwise the U87 and KM84 circuits are pretty much the same with a slightly different transformer ratio and of course the pattern option differences.

You could put a BV08 in this mic and a K47 or M7 if it would fit and it's basically a "Single FET U47" (not a FET47)... I wonder if we could parallel a couple FET's similar to how the ||6028 implementation works - reducing output Z and increasing drive capability of the active device.. I might experiment with that a little but the mic body in this thread would probably be too small for the BV08 :)

Cheers!
-j

I think that OP understand deemphasis network option - here we are "talking" about something a little bit different than U87 circuit ;)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: benqbasic on October 16, 2017, 01:04:38 AM
Yeah. CHeck out the U87 schematic and look at the signal path from top of FET (output) to C9 -to-  R8 and C6 (in parallel) which then feeds to the backplate... This is the negative feedback de-emphasis part of that circuit.

IOW -
The signal coming out of the FET is fed through an eq / filter (R8 and C6) which then causes modulation on the backplate. This modulation signal is band limited due to the filter and since it's on the backplate it is opposite in polarity and therefore subtracts from the signal produced on the front diaphragm and fed into the FET... Essentially a notch filter. I don't know the exact math but you can probably google that for more specifics on the filter frequencies / etc...

Otherwise the U87 and KM84 circuits are pretty much the same with a slightly different transformer ratio and of course the pattern option differences.

You could put a BV08 in this mic and a K47 or M7 if it would fit and it's basically a "Single FET U47" (not a FET47)... I wonder if we could parallel a couple FET's similar to how the ||6028 implementation works - reducing output Z and increasing drive capability of the active device.. I might experiment with that a little but the mic body in this thread would probably be too small for the BV08 :)

Cheers!
-j

Did you get a chance to try this?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: elskardio on October 20, 2017, 04:15:08 PM
Hi Guys,

I just wanted to share my version of this nice circuit. Have a great weekend  ;)

(https://s1.postimg.cc/7zldtzgodr/FET847.jpg)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 20, 2017, 04:47:01 PM
Hi Guys,

I just wanted to share my version of this nice circuit. Have a great weekend  ;)

(https://s1.postimg.org/7zldtzgodr/FET847.jpg)

Love it! Looks fantastic. Any chance of making your boards available?

The badge looks really cool, too.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: benqbasic on October 20, 2017, 07:00:33 PM
Hi Guys,

I just wanted to share my version of this nice circuit. Have a great weekend  ;)

(https://s1.postimg.org/7zldtzgodr/FET847.jpg)

Thats a good looking mic. What type of body did you use?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on October 20, 2017, 07:20:05 PM
Let me guess - does your version take forever to "come to life" too?

(Yes, i'm developing a pet-peeve with some bits of this design ;D )

Hi Guys,

I just wanted to share my version of this nice circuit. Have a great weekend  ;)

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: elskardio on October 20, 2017, 09:53:25 PM
Love it! Looks fantastic. Any chance of making your boards available?

The badge looks really cool, too.

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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 21, 2017, 08:04:32 AM
Finishing my Fet847 now,
firing up to bias fet.

I have some low-fq-noise, like AC hum,
but I get some signal to hum, just like 12db or some.
Any pointers where to get rid of the noise/hum?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on October 21, 2017, 09:26:41 AM
If the mic body's still open, and/or the headbasket isn't installed, that's where the hum gets in.

But just for the bias adjust, that's nothing to worry about, the test-signal will be way larger in amplitude anyway.

Finishing my Fet847 now,
firing up to bias fet.

I have some low-fq-noise, like AC hum,
but I get some signal to hum, just like 12db or some.
Any pointers where to get rid of the noise/hum?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 21, 2017, 12:26:12 PM
If the mic body's still open, and/or the headbasket isn't installed, that's where the hum gets in.

But just for the bias adjust, that's nothing to worry about, the test-signal will be way larger in amplitude anyway.
Oh, thanks a lot! That's good news :)

btw: Test signal and bias-adjust. How do I practically do it? Do I set it in front of my speakers?
edit, found this: https://groupdiy.com/index.php?topic=63889.0
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on October 21, 2017, 12:45:45 PM
Bit of a thread "necro", but here's a slight update / simplification :) https://groupdiy.com/index.php?topic=63889.msg853127#msg853127
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 21, 2017, 01:23:01 PM
Sound, wow,
and pleasant sounding!
I believe I have a working mic  ;D ;D ;D

Bit of a thread "necro", but here's a slight update / simplification :) https://groupdiy.com/index.php?topic=63889.msg853127#msg853127
Thanks!
I don't seem to have the right cabling/connectors right now, will order some.
https://www.ebay.com/itm/172679352208
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 23, 2017, 09:33:30 AM
Does the biasing affect more than max spl?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on October 23, 2017, 09:57:34 AM
Not really, no. More like, it affects the max undistorted SPL :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 23, 2017, 10:41:41 AM
Not really, no. More like, it affects the max undistorted SPL :)
Thanks!
Ok, then I can share my build :)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 23, 2017, 11:00:38 AM
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)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on October 23, 2017, 11:15:07 AM
Does yours take 5mins (or more) to reach "full" level too?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: G-Sun on October 23, 2017, 12:33:57 PM
Does yours take 5mins (or more) to reach "full" level too?
Can't seem to noticed there was anything like that.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on October 27, 2017, 10:32:54 AM
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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: gearhunter on January 24, 2018, 06:20:54 AM
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?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on January 24, 2018, 08:17:46 AM
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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: gearhunter on January 24, 2018, 09:13:24 AM
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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on January 24, 2018, 09:20:45 AM
What if you try recording some actual audio with the mic?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: gearhunter on January 25, 2018, 06:58:11 AM
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
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: francoisjonas on August 14, 2018, 06:35:02 PM
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
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Max51 on January 08, 2019, 05:04:34 PM
Hi everybody !

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

Thanks !
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Micmods on March 01, 2019, 01:45:00 AM
Could we get a photo of the back of the board?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on March 01, 2019, 08:59:27 AM
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?
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Wordsushi on March 01, 2019, 11:16:55 AM
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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on March 01, 2019, 11:27:48 AM
Duly noted ;D I still cringe when i see the dog's breakfast of a layout that the original is...  :o

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.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Strick9 on March 04, 2019, 08:52:03 PM
Duly noted ;D I still cringe when i see the dog's breakfast of a layout that the original is...  :o

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

I am also interested in one
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on March 05, 2019, 07:47:21 AM
I made a version that will fit BM800 bodies as well.
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: shot on March 06, 2019, 05:52:26 PM
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
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on March 08, 2019, 09:56:02 AM
If / since you already use Eagle, surely the layout's trivial enough to manually copy / recreate it, isn't it? :D

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
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: shot on March 08, 2019, 01:50:45 PM
If / since you already use Eagle, surely the layout's trivial enough to manually copy / recreate it, isn't it? :D

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

 8)

L
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Micmods on June 13, 2019, 05:54:56 AM
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
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Khron on June 13, 2019, 06:08:23 AM
(https://thumbs.gfycat.com/HighlevelPoorBluebreastedkookaburra-size_restricted.gif)

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?

Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: dasnevestheo on June 23, 2019, 05:42:38 PM
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)
Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: Max51 on June 25, 2019, 03:38:18 PM
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.


Title: Re: FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop
Post by: dasnevestheo on June 25, 2019, 04:30:55 PM
Thanks a lot, would love more details indeed :)