FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[G-Sun]

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?

 

[0dbfs]

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

 

[G-Sun]

and a microphone parts RK47.

Was this for the BM-800 body?
Did the capsule mount fit well?

 

[G-Sun]

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

 

[G-Sun]

What's this:

M22 sized hard ring mount for BM800 body

?

Or more precise: What's it for?

 

[G-Sun]

And btw:
Thanks a lot Dan for making highend and budget-conscious diy-mics available!

 

[Spencerleehorton]

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.

 

[G-Sun]

btw: Seeing that the AKG C414 using a c12 capsule.
How close do you think the Fet847 will be with a similar capsule?

 

[0dbfs]

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

 

[Wordsushi]

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?

 

[0dbfs]

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

 

[Wordsushi]

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

 

[0dbfs]

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

 

[Wordsushi]

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

 

[0dbfs]

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

 

[Spencerleehorton]

Only three of these transformers left for testing out now, if anyone's interested just msg me,

Regards

Spence.

 

[G-Sun]

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..

 

[Spencerleehorton]

yes, thats why the transformer i've had designed is nice and small and perfect for this build!!!

 

[0dbfs]

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

 

[Wordsushi]

Okay, pardon yet another noob question. What are the 75pf caps for? The ones marked on the BOM description as "Test-Capsule"?