TA27-Simplified u87 with RK12 or RK47and NTE10-3

[Ampampam]

Hello guys!

I bought some capsules in the group buy, and after my little disappointment with the rk12 in "The Tube" I wanted to find a good place for my lonely new capsule. The 847 was a good and simple design but I wanted to add a simple dc-dc converter to it. After checking many schematics I decided to draw a new schemo for my first homemade microphone. The basics are from the u87 Ai but the 160pF has been removed to kill the high frequency filter, so now it can be used with any flat capsule. The dc-dc converter came from the cad gxl3000. You can see almost the same on the audioimprov.com in the bm800 mod. Simple and good.  I would like to ask the more experienced professionals opinion of my schematic. Maybe you see something that I missed.  Will the capsule work properly in this circuit?

Thank you in advance!

 

[Ampampam]

Here is the schemo!

 

[Ampampam]

Actually thinking of simply supply the fet from  the phantom power without filtering. Sould it make such a difference? Less components and easier to make the board...

 

[Ampampam]

Okay. Here is the final format I think.

Anyone any thoughts?

 

[Khron]

You're still getting SOME filtering, by way of the RC filters (10u / 10k / 4.7u); you only eliminated what's called the "cap multiplier".

http://sound.whsites.net/project15.htm

 

[ln76d]

If you don't use deemphasis, better would be replace whole feedback network with 4pF capacitoras in KM84.
Otherwise remove 47nF, 6.8k, 560r - it's a part of low end filtering. Or at least make 470nF.
Problem with RK12 is that these type of chinese capsules have nothing to do with CK12.
It's just K67 backplate with edge termination. Hi freq bump is only a little bit lower than in K67.
Backplate pattern is identical 1:1 so i assume that the little change in freq is caused by termination.
If you have no problem with RF, remove inductors and 330pF caps.

 

[Ampampam]

Yes, it still have some filtering. I think it will be enough.  I don't want to remove the low cut filter, and was thinking to replace the 160pF with something like 4pF but it is pointless, since it should not do anything. (Less with one components.) By the way the circuit received the same 4pF as the km84 has, but in the wrong place. It supposed to be between the gate and the drain to prevent feedback. I don't know egy  I put it like that... Does it make sense that way?

 

[Ampampam]

Hello everyone!

I had some spare time this week. I made the PCB for the motherboard. If you ask nicely, I can make the power supply as well, but I made it red neck style for example.

 

[Ampampam]

Some more

 

[Ampampam]

And the last bit...

 

[Lowfreq]

Did this mic ever get built?

Any hiccups? Or did it all go well?

 

[Ampampam]

Hi

The mic has been built after all and a hand drawn board has been used for the +/-60 Volt power supply circuit. The mic itself has a relative low noise floor and low output, so you can drive the preapm a bit hot with it. The sound  is bright and open but nothing special. Basically the capsule produces the sound characteristics and the fet transfers it via the transformer with a tiny bit of added harmonics. It sounds great despite that it has a Chinese capsule. The high frequency roll off has been completely removed so the capsule can bring its high end details to its full potential. It picks up sibilance fairly easily, but it is okay. You can have a good use of it on almost any instruments (it was good on kick and guitar cabs) but if you do not have better choice for vocals it will do the trick. If you have any questions let me know please.

Ps.:I think there was an issue in the schematic where 47nf has been put instead of 470nf if I remember well. (in the filtering circuit of the capsule.) For this reason the mic did not produce any sound in the beginning. After fixing it it has worked without any problem.

 

[Drosselmeier]

If you have any questions let me know please.

Greetings! I also build Neumann mics for poor people Why have you removed С102, R103, R104 from DC-DC?

 

[Ampampam]

Hi all,

Actually the mic was sitting in the drawer for a couple of years because it does not function exactly as expected. I am hoping if anyone can give me some inputs on this.

For some reason it feels like it is missing some low end, like if the bass cut would be turned on constantly. Attached the schematinc and some pictures. Does anyone have any idea what should be causing this?

I know the build quality is not really outstanding Also the DIP switch was removed for testing purposes.

 

[mhelin]

Keep the wires from the capsule short and the connection in high impedance areas free from leak to circuit board - meaning connect the wire from the capsule to the input cap and from there to the 1G resistor and FET in air (lift the pins) or use a special insulated pin, see
https://microphone-parts.com/pages/insulate-high-impedance-connections

 

[Ampampam]

Keep the wires from the capsule short and the connection in high impedance areas free from leak to circuit board - meaning connect the wire from the capsule to the input cap and from there to the 1G resistor and FET in air (lift the pins) or use a special insulated pin, see
https://microphone-parts.com/pages/insulate-high-impedance-connections

Thank you for the advise! Actually it seems to be very quite. Used it couple of times as mono overhead and it worked great, but the main issue is that it has weak low frequency response. Maybe the transformer should be the issue? Also in Figure 8 mode it acts like cardioid, I forgot to mention that.

 

[Flatpicker]

Increasing the value of C4 should give you more low end. Try a 10uF here.

 

[Drosselmeier]

Also in Figure 8 mode it acts like cardioid, I forgot to mention that.

without cap c102 the fig "8" won't be working