New-ish electret capsule

[micolas]

I'm about to try this capsule in a Fame CM2 mic, but I have no experience with electret capsules yet. Diaphragm goes to ground, but how do I connect the permanently polarized backplate to the gate of the fet? Since in this Schoeps circuit there are a low voltage applied to the fet gate, should I place a cap between them?

Edit: connected without a cap and seems to work BTW it sound super nice!

Thanks!

The stock microphone has a rather high noise, 24dB A, with the original capsule. The new electret capsule I suspect provides a lower signal than the stock one. How is the noise, has the S/N ratio gotten worse?

 

[LevinGuitar]

Indeed I had some noise with the original circuit but I couldn't find where it came from, tried some filtering after the zener and so... so I removed the pcb and installed a diy KM84 circuit with u87ish deemphasis.

 

[micolas]

Indeed I had some noise with the original circuit but I couldn't find where it came from, tried some filtering after the zener and so... so I removed the pcb and installed a diy KM84 circuit with u87ish deemphasis.

So the circuit is not linear now and the electret capsule benefits from u87ish deemphasis? This accentuates the mids a bit, makes them stand out in the mix. Does the transformer have a 7:1 ratio?

 

[LevinGuitar]

Right! The capsule is quite bright in a flat circuit. Yes, around 6.5:1. Bought them in the old WGT site, not working anymore. Quite nice for the size. I asked the manufacturer about them but they don't have stock since time ago

 

[micolas]

@LevinGuitar
A colleague from the group is looking for a circuit to replace the one with SMDs in the MXL990. I think your approach would be interesting, with or without de-emphasis, depending on what the capsule will procure.

 

[micolas]

@LevinGuitar
You actually gave me a great idea with this circuit.
I have a lot of mics that sound
super-clean: B2-pro, Studio Projects, Rode, Neumann TLM103, etc, so I'd like something with more character, color, transformer saturation.
I was just wondering what to do with these great bodies.
Thanks!

 

[LevinGuitar]

I use that circuits becasuse (for now) I haven't found a way to implement a nice deemphasis in the stock one keeping low noise and distortion. I tried different approaches but none work enough for me. Otherwise I would be happy to save time and money in parts

 

[Paul W]

https://a.aliexpress.com/_mKDg9LB

I just wanted to do another heads up on this capsule for couple of reasons.

- It sounds really good, measures great, smooth high end boost, no crazy notch dips, great low end.

- I dare to say it reminds me of a good C12 capsule.

What does that mean? Does it measure like a C12 (in cardioid mode?)? Is its off-axis sound somehow C12-like?

I've heard things about the lovely off-axis sound of a real C12 but I have zero experience with them or insight about them.

I've also read that the current C12 mics from AKG aren't like the classic ones, and don't know how to interpret "good C12 capsule" in light of that.

 

[micolas]

Indeed I had some noise with the original circuit but I couldn't find where it came from, tried some filtering after the zener and so... so I removed the pcb and installed a diy KM84 circuit with u87ish deemphasis.

I see you use carbon resistors. If they are on the power side, it's fine. But for the audio part, for many years I have been using metal film resistors, they have lower noise. (Indeed in radio frequency they can behave like inductances)

 

[Dylan W]

Any thoughts about how this compares to the Primo EM21?

 

[Paul W]

In the "Looking for electret capsule manufacturer recommendations" thread, kingkorg recommends a "newer version" w/o screen, and says its FR is flatter (and provides a nice plot). Posting here so that anyone looking at this thread can find the other version. (If only me, after I forget again.)

https://www.ebay.com/itm/25mm-Large...Recording-Condenser-Mic-Capsule-/313832436024

That eBayer doesn't ship to US, but k brown found this listing for what appears to be the same capsule:

https://www.ebay.com/itm/255415516289

kingkorg's post with FR plot for the new capsule:
https://groupdiy.com/threads/lookin...rer-recommendations.80083/page-2#post-1029138

 

[Paul W]

Noob question: what are the shielding requirements for these kinds of capsules?

Am I right to think that the shell and the diaphragm (and the screen in front of the diaphragm on the version with screen) are grounded (in typical use) and RF can only get in from the rear?

I seem to recall a thread where somebody reported RFI problems with BM-type mics with only coarse mesh headbaskets.

I have a couple of BM-700's I've modded the circuits of that have only a single somewhat coarse layer of metal mesh (with foam layer inside) and I'm wondering if that's enough. If it's not, can I attach a piece of window screen on the back of the capsule to shield it? Will the leads to the capsule pick up significant RF? Would using shielded wire fix that?

Am I better off putting the kingkorg v1 capsules (with screens) on the BM-700 mics with one-layer mesh, and the kingkorg v2 capsules (without screens) on the BM-800's with a finer layer of metal mesh inside the cylindrical headbasket?

Or does it not matter?

 

[kingkorg]

Am I right to think that the shell and the diaphragm (and the screen in front of the diaphragm on the version with screen) are grounded (in typical use) and RF can only get in from the rear?

You are right.

I have a couple of BM-700's I've modded the circuits of that have only a single somewhat coarse layer of metal mesh (with foam layer inside) and I'm wondering if that's enough. If it's not, can I attach a piece of window screen on the back of the capsule to shield it? Will the leads to the capsule pick up significant RF? Would using shielded wire fix that?

You will neet to test this. I have personally used, as you named it, KK V2 without any shielding. Idk if i'm being lucky with where i use the mics. Shielded wire could add to parasitic capacitance and increase the noise.

Here's this one for ideas. I use it just like that, i did add shielding mesh behind it.

Post in thread 'Cad Equitek E100 Capsule' https://groupdiy.com/threads/cad-equitek-e100-capsule.77061/post-1043509

 

[Paul W]

You are right.


You will neet to test this. I have personally used, as you named it, KK V2 without any shielding. Idk if i'm being lucky with where i use the mics. Shielded wire could add to parasitic capacitance and increase the noise.

Here's this one for ideas. I use it just like that, i did add shielding mesh behind it.

Post in thread 'Cad Equitek E100 Capsule' https://groupdiy.com/threads/cad-equitek-e100-capsule.77061/post-1043509

Am I understanding what you did there correctly that

1. You put the FET right on the back of the capsule so that the wire from there would be at high impedance rather than low, and less susceptible to RFI (I do not actually understand amplifier circuits in any detail, especially how the feedback path actually works, so I don't know if that even makes sense), and

2. you put the wire in a big grounded tube, rather than a little bitty one like a shielding jacket, so that it wouldn't mostly be close to the conductor and create a significant capacitance.

I have another BM-700 type mic sitting here that doesn't actually have a FET populated on the circuit board in the marked FET place, but otherwise the PCB looks like the classic one in Spragen's how-to, so I assume that there's a FET in the back of the VERY small electret. (I'm pretty sure this was a "Neewer NW-700," in case anyone wants to be warned off of them, but I've swapped bodies around and am not absolutely certain. But hey, the PCB is a nice red.)

I've been leery of using that mic because the PCB lacks the FET and the paint-by-number mods don't apply, but I guess it's pretty straightforward to either mount one in the obvious place on the PCB, or stick it on the back of the electret capsule as you did...

(Can someone say what FET I should get? Does the PCB look normal for a BM-800 type mic, other than lacking the FET on the board?)

 

[kingkorg]

1. You put the FET right on the back of the capsule so that the wire from there would be at high impedance rather than low, and less susceptible to RFI (I do not actually understand amplifier circuits in any detail, especially how the feedback path actually works, so I don't know if that even makes sense), and

It's the other way around, but you got the point. Capsule to gate is high impedance. And the lines going through the tube are lower impedance, and less susceptible to noise, parasitic capacitance. They can run quite long.

I have another BM-700 type mic sitting here that doesn't actually have a FET populated on the circuit board in the marked FET place, but otherwise the PCB looks like the classic one in Spragen's how-to, so I assume that there's a FET in the back of the VERY small electret. (I'm pretty sure this was a "Neewer NW-700," in case anyone wants to be warned off of them, but I've swapped bodies around and am not absolutely certain. But hey, the PCB is a nice red.)

That thing does basically the same thing i've done, the fet is behind the capsule. Regarding the fet, search the forum, there's been quite a few discussions which fet to choose. If you are not particularly picky, or want to spend eternity shooting out fets, safe bet would be j113.

 

[pmfalcman]

In the "Looking for electret capsule manufacturer recommendations" thread, kingkorg recommends a "newer version" w/o screen, and says its FR is flatter (and provides a nice plot). Posting here so that anyone looking at this thread can find the other version. (If only me, after I forget again.)

https://www.ebay.com/itm/25mm-Large...Recording-Condenser-Mic-Capsule-/313832436024

That eBayer doesn't ship to US, but k brown found this listing for what appears to be the same capsule:

https://www.ebay.com/itm/255415516289

kingkorg's post with FR plot for the new capsule:
https://groupdiy.com/threads/lookin...rer-recommendations.80083/page-2#post-1029138

(in my best Jeremy Clarkson voice):

I went on the internet and I've found this:

https://pl.aliexpress.com/item/1005...95e2657!12000035564573978!rec!PL!727804860!XZ

Newer version, no screen.

 

[k brown]

(in my best Jeremy Clarkson voice):

I went on the internet and I've found this:

https://pl.aliexpress.com/item/1005006064243335.html?spm=a2g0n.detail.1000014.6.277c0kXG0kXGKV&gps-id=platformRecommendH5&scm=1007.18499.315613.0&scm_id=1007.18499.315613.0&scm-url=1007.18499.315613.0&pvid=fd985f10-f88e-4893-a18d-819f225e2ef5&_t=gps-idlatformRecommendH5,scm-url:1007.18499.315613.0,pvid:fd985f10-f88e-4893-a18d-819f225e2ef5,tpp_buckets:668#2846#8112#1997&pdp_npi=4@dis!PLN!30.13!29.50!!!7.63!7.47!@21038e8317244268719851095e2657!12000035564573978!rec!PL!727804860!XZ

Newer version, no screen.

Highway robbery!

What's next - they gonna send a capsule to anyone who mails a self-addressed, stamped envelope?

 

[pmfalcman]

What's next - they gonna send a capsule to anyone who mails a self-addressed, stamped envelope?

Hope dies last...

 

[LevinGuitar]

The way they are shipped, the screen becomes useful

 

[k brown]

The way they are shipped, the screen becomes useful

True, that.

Has there been a version of that capsule with a screen (the one with the plastic/fibre(?) rear plate)?