Some question from noob about capsule rk-12

[Андрій Чубака]

Did you omit and install jumper in position of D8 and Trimpot of voltage multiplier board?

but I still not sure need I am this or not? Trimpot here is 10k I guess

 

[oscarhuang]

Two possibilities are causing your microphone not to work. The first is that the polarization voltage is too high, and the microphone diaphragm sticks together. The second is that the backplane of rk12 is two pieces, your lead screw may be on another backplane.

 

[Андрій Чубака]

At this moment microphone is working but i want made new hex dc dc pcb and try with it. I want know need i trimpot in this case or not? I guess it is for regulation hex dc dc voltage but here True Condenser OPA Mics it is didn`t used

 

[Андрій Чубака]

So guys I made this mic with help from this forum and I made some tests. This what I can say about all it. This capsule with this preamp from jules psb possible use only with equalizer. In other case sound is too much on high frequinces. But with equalizer sound is very flexible, bass boosting works very well without distortion and very possible get really natural and bright sound like from really good mic with large diaphragm. But level of output sound from mic was low and I decide replace 1 gom resistor with 1 mom. It was very helpful but later mic just broke down I guess some problem with opa1642. Now I thinkig what I will do next. I not so need this mic. And I make it just for test mic with 40-50$ price. And this is some my result what I have for now. Thanks all for help. If I will have possibility later I will upload some sound tests but now it is not possible.

 

[Андрій Чубака]

Now I guess problem here is in not original opa1642. I replaced with good original tl072 and now here is good level output signal, also now sound is balanced not like on high frequencys only.

this is some test on tl072, it is cheap maybe 0,3-0,4$, latter I will write more about different chips.



Also here is my cute pcb and broken opa1642:/

 

[Андрій Чубака]

Strange problem here looks like tl072 later broke down also. THis time I don`t used 1 mom resistor insted of 1 gom. when it is happen vortage on xlr drops from 20v to 15v and level of output signal is drop also. Very strange problem

 

[Khron]

Can you remove the screws of the opamp board (but don't disconnect any wires), and flip it so we can see the bottom as well?

 

[Андрій Чубака]

Here is nothing spectacular I am anyway try fix it now. I guess opa pcb i will rebuild later one more time bit more clear. But now i must found where is problem with broke down chips on it. At this moment i found this. Between 5 and 6 legs of already broken tl072 i found some resistance around 40 mom. But i still have one more new tl072 and there i don't found this. Other pins looks like about same on both differences only about like in different manufacturers. Maybe i will try replace 200 om resistor on 330 om like i found on other circuit diagram and will try one more time. But i not sure about problem exactly about it. Just maybe.

I am already replaced tl072 on new and replaced 200 om resistor on 330 om in opa alice circuit. So this new tl072 sounds more bad than previous from different manufacturer.

 

[Андрій Чубака]

One of reason why all this can happen it is because when I turn on phantom power on sound card there is some jumps with power maybe it is just broke down chip. I don`t have good osciloscope for decect this problem. but on audio recording in is looks like this. if my teory is correct in this case better have 330 om insted on 200 om and also better have additional capasitor 47uf between 4 and 8 legs of chip. Or even some induction on this line.

 

[Khron]

Is the regulating zener diode installed, and functioning? What voltage can you measure between opamp pins 4 and 8?

 

[Андрій Чубака]

Yes zener diod is working. Like 11,5 v on 8 leg. But when chip is broke down there voltage is drop also.

Soon i will update this circuit with new parts. And after this i will know for sure there is problem or not.

 

[Khron]

Are the output capacitors still ok, and in place?

 

[Андрій Чубака]

Wich is on xlr port? I will check later but I guess they are durable. Different impulses is more dangerous for chips than for capacitors.

I not sure now where is real problem. But regularly different impulses doesn't have enough amperage for broke down capasitors. But sometime they can travel far away on circuit if circuit is not enough protected. So first of all i must try this.

 

[Khron]

Might not be a bad idea to include some protection diodes on the output of the opamp then.

https://e2e.ti.com/support/amplifie...the-part-sensitive-to-power-supply-sequencing

 

[Андрій Чубака]

I checked all one more time. And all working normally, only chip is broken one more time, so it is like starting one time normaly after placing, but after starting second time chip is alredy broken. Voltage dropping in this case exactly on chip. Now I will try do new more clean pcb with more protection and will try one more time. good this tl072 is cheap so I have enough try. about meashuring resistance on broken one and new I can`t confirm my prewious info about 5 and 6 leg of chip. now it is look like ok, but chip doesn`t working anyway.

 

[kingkorg]

I'm not really sure what you are doing here. You absolutely have to use the original Op Amp as intended. Tl072 won't work for various reasons. Also you can not drop the value of 1Gig resistor to Mohm range. Follow the original instructions and the mic will work. It doesn't get any cheaper or simpler then the original schematic.

 

[Андрій Чубака]

So maybe problem was with old opa pcb. I don't know for sure now it was self made and everything is possible. I made new and i have very different result than it was before.

here is some new sound test with same scenario direct sound from mic on same tl072.


About will be my problems with chip solved in this case I will know later. But now it is works just fine. Also I am added some inductance to power suply line of chip to leg 8 in this case. it is 4,7 mkhenry I get it from some small broken dc-dc converter.

 

[Андрій Чубака]

I'm not really sure what you are doing here. You absolutely have to use the original Op Amp as intended. Tl072 won't work for various reasons. Also you can not drop the value of 1Gig resistor to Mohm range. Follow the original instructions and the mic will work. It doesn't get any cheaper or simpler then the original schematic.

i know all this but when chip is broke down on psb every time put new and expencive chip every time is not solution. Also you never can be sure have you original chip or not. Now almost everywhere copies from china one is with more better quality other one is just very poor quality. In this case I do all best what I can. and first of all I must fix pсb problems.

I am not like noob in soldering, but about building mics I almost don`t know nothing before so because here all going like now. It is not like a big pro project but as for me result is interesting. Full price of this mic like I tested now around 40$ it is with body and capsule. But of cource I spended more with alredy broken chips and new psb. But this is my problem

 

[Khron]

Also you never can be sure have you original chip or not. Now almost everywhere copies from china one is with more better quality other one is just very poor quality.

Well, that totally depends where you get your chips from...

 

[kingkorg]

i know all this but when chip is broke down on psb every time put new and expencive chip every time is not solution. Also you never can be sure have you original chip or not. Now almost everywhere copies from china one is with more better quality other one is just very poor quality. In this case I do all best what I can. and first of all I must fix psb problems.

You absolutely can by ordering from something like Mouser. Also you can check quiescent current to be sure, and drive capabilities. You are wasting your time with TL072, if nothing else noise will be terrible, THD, and drive capabilities. Have you checked current and operating voltages with the TL072? If your component source is sketchy, you can't be even sure it's TL072.