Cad Equitek E100 Capsule

[Wordsushi]

Sure, why not. One might try with or without polarization applied.

Kingkorg,
Do you know what the Equitek polarization is? Was it hitting the CP-1 capsule with a full 48v?

 

[kingkorg]

Equitek E100? No polarization applied, the capsule is electret, it doesn't need it. But you might want to apply some voltage and see how it affects the sound and if it does.

 

[Harvey Birdman]

Thank you very much, King. Yes, I have seen that link. I've been searching for everything I can find out these mics. This guy definitely has a comprehensive description of the mod process that even I can follow. I actually used the instructions on that page to take mine apart and will probably use this on the second ME80 I ordered. My guess that mine has been recapped comes from what the photos on that page look like. You're absolutely right about it being very plosive prone on its own. I even tried it with the Hakan pop killer, but I've had a lot of luck so far using the included grill head on it, which seems to effectively kill pops at 4 inches away. I'm also pointing it down and to the side of my mouth, which also has the benefit of keeping it almost entirely from my eyeline when reading copy so it's all good. I really am pretty stunned by how these mics sound. My brain spins at the potential projects that can be done with this capsule.

 

[Wordsushi]

I guess my question really is how much voltage can/should you apply to the capsule with to hit that sweet spot with noise and sensitivity? MicUlli mentioned 30v in his post about testing capsules. Stephen Sank, the Nakamichi tech, does a phantom and circuit mod, that tapers rave about, where he mentions also raising the voltage to 20.

I think the 3 things I want to try at some point are:
1 - phantom mod
2 - Gutting one and replacing the entire circuit in original body to use with the CP1/EM21 capsule.
3 - Putting the EM21 capsule atop a good circuit inside an LDC style body - possibly with a transformer.

​

​

 

[k brown]

Here's the circuit I have in my Teac/Tascam bodies.

It's a mod of the Pass B1 Buffer, using 2SK170BL.

The 'preamp' parts before C100/200 are not used, of course. R103/203 are replaced with 1G. Runs a good long time off 3 9v batt.

Since they're only ever used as spot mics, they're run unbalanced with short cables, into pres placed right at the mics

 

[Wordsushi]

Here's the circuit I have in my Teac/Tascam bodies.

It's a mod of the Pass B1 Buffer, using 2SK170BL.

The 'preamp' parts before C100/200 are not used, of course. R103/203 are replaced with 1G. Runs a good long time off 3 9v batt.

Since they're only ever used as spot mics, they're run unbalanced with short cables, into pres placed right at the mics

That's pretty cool. I only plan to use them to spot mic my voice. Do you have pictures or by chance, dare I ask.... boards?

 

[Wordsushi]

This guy has an interesting breakdown of refurbing a stock Nakamichi CM-300, including a nice pic of the small circuit board with the FET in the area underneath the capsule with instructions how to access it.

https://audiomods.datsunzgarage.us/cm300/

 

[k brown]

That's pretty cool. I only plan to use them to spot mic my voice. Do you have pictures or by chance, dare I ask.... boards?

No boards; only one of the FETs and a couple of resistors point-to-point in the mics; the rest in a two-channel battery box.

 

[Icantthinkofaname]

By adjusting the plastic backplate or whatever it is, is it possible to make it actually figure 8?

 

[kingkorg]

Nope. By the point you release the screw that much the air cushioning will be gone, and the response turns into awful sad face curve.

 

[Wordsushi]

Frankensteined a phantom power mod into the Teac ME-80. 12v Zener. Sounds cleaner than before mod. Instead of a shunt in the battery compartment, I hardwired it from the power board to the fet board under the capsule.

I know one of the better known Nak mod guys the tapers rave about does his mod at 20v, so I may try that next with one of the same mics I have here. It's a tight fit so it really had to be shoehorned back in. Going to try a couple different mods including the cool Vac11 mod, which smartly stuffs all the good stuff into the repurposed battery compartment.

I'm still curious how much voltage I can hit this circuit with.

 

[MicUlli]

IMHO the most prominent fault in modding this mic is to leave the input circuit untouched. The original JFET (2SK118O) has a very low forward transconductance and is therefore noisy and limited with respect to undistorted output.
The second fault is reusing the transformer because it is not shielded against magnetic fields and limited regarding output signal capability because of magnetic saturation.

BR MicUlli

 

[Wordsushi]

IMHO the most prominent fault in modding this mic is to leave the input circuit untouched. The original JFET (2SK118O) has a very low forward transconductance and is therefore noisy and limited with respect to undistorted output.
The second fault is reusing the transformer because it is not shielded against magnetic fields and limited regarding output signal capability because of magnetic saturation.

BR MicUlli

I was expecting the 2sk1180 since I had seen the same in a photo here. This ME-80 I opened up has a K30a fet in it. Apologies for the blurry photo. I wasn't sure why it sounded different from the others I have until I peeked inside and saw this.

So it begs the question, what FET and what transformer would be optimal replacements?
I've added the CameraTim phantom mod schematic below.

 

[MicUlli]

2SK30AO and 2SK118O are nearly identical. Source resistor seems to be 1,2K according to your picture.
I will take some measurements for the original performance (noise and THD and sensivity) and post them tomorrow.

BR MicUlli

 

[MicUlli]

Now it is done. Find attached the diagrams.

1. The original circuit has a sensivity of -55,2 dBV @ 94 dB SPL and a noise floor of -130,1 dBVA -> SNR = 74,9 dBA
2. The MicUlli-mod has a sensivity of -37,7 dBV @ 94 dB SPL and a noise floor of -120,7 dBVA -> SNR = 83 dBA
3. The original circuit shows unacceptable THD from 104 dB SPL upwards.
4. The MicUlli-mod takes 124 dB SPL without significant THD.

Test setup: capsule removed, instead 55 pF ceramic cap connected to audio out and input pin from capsule. For the original circuit the input voltage was 10 mV @ 94 dB SPL, for the MicUlli-mod it was 14,1 mV @ 94 dB SPL because of taking the additional polarization voltage of 30V into account.

My modification can be found here in this mic forum, I actually haven't the exact position in mind..

Conclusion: 17,5 dB more output level, 8,1 dB SNR improvement, lot more than 20 dB overload capability improvement
BR Ulli

 

[rock soderstrom]

High quality post, Ulli!! Thanks a lot

Thread with your headamp design is here:

https://groupdiy.com/threads/a-very-versatile-input-stage-for-sdc-mics.80172/

 

[analogguru]

For the original circuit the input voltage was 10 mV @ 94 dB SPL, for the MicUlli-mod it was 14,1 mV @ 94 dB SPL because of taking the additional polarization voltage of 30V into account.

Conclusion: 17,5 dB more output level, 8,1 dB SNR improvement, lot more than 20 dB overload capability improvement
BR Ulli

No wonder without the original step down transformer....

 

[k brown]

What I could never understand about these Teac/Tascam/Primo mics, is that in the original circuit, the audio seems to go through the battery - how can that be good?

 

[k brown]

Nope. By the point you release the screw that much the air cushioning will be gone, and the response turns into awful sad face curve.

From your experiments, can the cards be turned into omnis, just by unscrewing the disc, removing the foam ring, and screwing the disc back down all the way?

 

[kingkorg]

Sure, you don't even have to remove the foam, just screw the ring tightly, might be even better that way, the foam will act as a gasket.