FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[0dbfs]

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

 

[Wordsushi]

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.

 

[G-Sun]

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.

 

[elskardio]

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

 

[ln76d]

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.

 

[Wordsushi]

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?

 

[ln76d]

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

 

[Wordsushi]

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!

 

[ln76d]

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.

 

[Wordsushi]

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? 

 

[ln76d]

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.

 

[Wordsushi]

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!!

 

[G-Sun]

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.

 

[maq3396]

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

 

[poctop]

Yes they are still listed and in stock ,
last item on this page,
http://www.vintagemicrophonepcbkit.com/orders.html
Best,
Dan,

 

[maq3396]

OOOps...didnt check the order page!

Thanks Dan

Cheers
Mac

 

[tommypiper]

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. 

 

[Rasta3]

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.

 

[poctop]

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,

 

[Rasta3]

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