FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[rockinrob86]

I finished mine over the weekend!

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

Took a look at this tone on  my scope:

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

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!

 

[Khron]

Are there supposed to be photos within the post?

 

[Winetree]

What capsule and transformer did you use?

 

[rockinrob86]

The cinemag 5722, and a microphone parts RK47.

 

[midwayfair]

...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.

 

[vinylwall]

Hi Dany.  I'd pick up a pair of PCB's if you did another run.

 

[poctop]

Another small run is now launched,
So if anything please post , 
thanks,
Best,
Dan,

 

[fsalter]

Yeah sure...a couple more for me Sir Poctop

 

[Spencerleehorton]

I'm still waiting for some components and mic cases!! Seem delivery from China is very hit and miss at the moment!!!!

 

[Spencerleehorton]

These just arrived!
Time to get to work!

 

[Spencerleehorton]

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.

 

[poctop]

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.

 

[felixskw]

Count me in for 2 please.

Thanks,
Felix

 

[Spencerleehorton]

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.

 

[Spencerleehorton]

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.

 

[Khron]

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)

 

[0dbfs]

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

 

[ln76d]

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?

 

[Khron]

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)...

 

[felixskw]

Dan, I would like to know the price too, please.

Thanks,
Felix