This mod indeed polarizes the backplate. But the colors are mixed up. Blue is the backplate, if we're talking about the original capsule.

Last night I installed the Maiku K12 capsule. Quite happy with how that sounds.
But now I'm thinking about ways to make it multi-polar. With a remote from the power supply. Why let a back membrane go to waste?
I have to look into this, but I have a feeling that should be do-able.

About the power supply voltage. If you want to replace the tube with a 6072 then I think 120 Volt makes sense. For a 12AX7 or a 12AT7 I don't think it is necessary to change it.
But what do I know?

You could replace R3 with a variable resistor to set the polarization voltage to whatever you like.
Rather add a say 470 KOhm variable resistor before R3 and you can regulate the voltage between 51 and 96 Volt.

I read that the polarization voltage also depends on the capsule. Thicker membranes can take higher voltages.
60 Volt is ideal for 3 micron capsules, 6 micron can take higher, like 80 Volt. I'm just repeating what I read.

Lowering the voltage decreases sensitivity. Half the voltage gives a 6 dB reduction. Too high a voltage and the membrane can stick to the backplate, which is bad.

In theory you want to have the voltage as high as possible without it being too high. The more sensitive the capsule, the better the signal noise ratio.
If that is too much for the output transformer, then I would be more inclined to swap the tube for a 12AT7.

All in all I can't help thinking that whoever designed this microphone must have had some understanding of what he/she was doing.

If you connect the rear diaphragm wire through a SPST toggle switch to ground you will get OMNI when the switch lifts the rear diaphragm off ground you get Cardiod. Simply as that

I don't think that will work as it is the diaphragm that is polarized and not the backplate. Not sure if you can just swap the wires.

As we both noted there is a connection for polarizing the backdiaphragm, complete with components, on the PCB. Probably they are using the same PCB for a different mic that is multi-pattern.

But that also needs a switch on the power-supply. I think that by varying the polarization of the voltage on the backplate you can create various polar patterns.

I'll have to study the schematic of a C12 to understand how it works exactly.

Continuing to take small steps on the learning path. I came across a schematic for a U67. The power supply is 210 Volt. That sort of confirms my idea that the power supply voltage depends on the tube and what is good for one is not necessarily good for another.

I also continued experimenting. I have now installed a switch on the mic so I can choose between omni and cardioid mode. I also changed how the capsule is hooked up. The baseplate now receives the polarization voltage, instead of the diaphragm. I have included a schematic of my changes. Changes are in red, removed components in grey. I removed the 1 GigaOhm resistor, as well as the 1 nF capacitor. The capacitor created a highpass filter with the 200 MegaOhm resistor R6. Inserting these values in an online calculator told me that the corner frequency is 0.7 Herz. Not sure what good that does.

I was a bit worried about my changes but the mic still works as before. I could be wrong but it seemed the output is a fraction lower now. It also feels a bit more dynamic. Maybe because of the removed resistor?

I'm not sure if I'm going to keep the C12 capsule. It is a bit bass heavy. I might try a K47 instead.

I'm glad I found this thread!

I'm not much of an (mic) electronics guy so I haven't touched the circuit board of the mic or the PSU but I did change out the tube.

I did not have (another) 12AY7 at hand but I did have a spare JJ 12AT7 so I tried that.

Of course it's less than half the gain factor of the 12AX7 but it sounds surprisingly good.

Last week, inspired by some of the cosmetic mods I've seen here, I decided to take out ye olde rattle can and painted mine black.

Blue and gold looks very "Royal" and all but Black & Gold looks so much more the part. (Got a bit of that vintage JPS bling going...)

Thanks for the inspiration all!

Before you change capsule you can try to tune mic by changing capacitors.
- use 2.2μF - 400v capacitor for C8. This way any resonance between the inductance of the output transformer and C8 falls into the sub-sonics below the audio range.

-Other useful trick is to reduce resonance of headbasket by adding dampening material to the base. Install a porous damping material inside at the bottom of a round (at the Plate where the Capsule holder is installed). That will sort any issues with comb filtering and resonance as well.

I have here Maiku K12, K47 and K87. K47 is my least favourite.
I really like K12 in combination with 12AY7, it works well with just about anything I tried so far, vocals, drums, acoustic instrument. Very smooth and open capsule. Second favourite is K87 in combination with Mullard 12AT7 military grade. Mullard is dark sounding tube, it almost have natural hi-freq roll off just like you would use with K87 type capsule.
k47 has mid-low range (200-300hz) bump that works nice for some vocals or bassy instruments, but in most cases is to much. hi-freq is nothing special as well, it still sounds harsh to me. Maybe It might be good match for Rode mics.
The capsule that impressed me most lately is M7 from ebay. The most balanced sound, it takes EQ great. Sounds almost like really good ribbon mic but more focused. It beats way more expensive capsules available.

I happened to have a 2.2 uF polyester something capacitor lying around. Unfortunately it's only 100 Volt. Bad luck.

I might try that. I did remove the inner mesh of the headbasket today. A bit of a gamble and not really well thought over. But I think I like it better.

I installed the K47 anyway. I can always take it out again. I did some test recordings that I yet need to evaluate.

Do you mean 2K to 3K? The k47 is known for a presence bump in the high mids. It should not be that low, I think.

Interesting. They say that M7 capsules don't last that long though.

Moder M7 capsules are made from materials that don't have lasting issue. Maybe you refer to original M7 Neumann that was made of PVC plastic, before they moved to K47 capsule, those indeed had lasting issue as PVC material made in those time was not that good.

All Maiku and other 'clones' K12,K47 and K87 capsules are made from Chinese backplates at the best, in most cases it's rebranded Chinese capsules. In reality they don't have anything to do with CK12, K47 or K67 original design. Those capsules are tuned to meet specs of original capsules and thats all, thus they all suffer from harsh and spitty hi-end boost. To me K12 ( only edge terminated capsule) seems to be the most balanced and usable.
M7 is completely different story, it is improved version of original capsule made with moder technology and materials that last.

It just crossed my mind an issues I had with Maiku K12. The way capsules are tuned diaphragmon one side is dark and boomy and other one is balanced . Make sure you test both sides and use balanced one as front diaphragm.

I haven't noticed that. I will test it.
You seem not too impressed with Maiku capsules? Myself I don't know really. They seem to be alright but maybe that's because I have never used a great capsule.
Still struggling to find a mic that I really like on my voice. But the problem could be very well on the other side of the capsule .

I'm thinking of buying a SCT-2000 and put the K12 in there. I'm guessing it uses the exact same PCB?

Maiku is fine for a budget capsule, he claims that he QC and re-skinns chinese capsule. I find that Maiku and 20eu Chinese capsule from Ebay looks and sound exactly the same.

In my SCT-2000 mod I used Maiku K47 capsule and UTM transformer. It was tight fit, had to cut bell around transformer, but it works. Shape of head-basket plays a role in response of the capsule. k47 might be better choice for sct 2000/sct700.

Rode capsule in combination with darker sounding tube in SCT 800 might be a winner.

Sorry to revive this older thread. I've got a question on the PSU mods you suggested:
Would a 68V 1W zener diode work just as fine? Or does it need to be 62V 1.3 W?

Thanks in advance.

Hi,
I never tried but believe It will work fine with 68V.
The point is to be close to 120V when measure R1 in the mic.