Diy Aliepxress u87 cardiod microphone build Help

[khalidgul]

Dear All,
I hope this finds you best both in spirit and health,
I am very new to this and interested to learn.I took courage and bought a microphone board it says upgraded u87 cardioid large diaphragm mic pcb.Also I bought a cardioid microphone capsule.As I have received the the package and assembled the parts into bm800 body, there is huge hum,and low voice levels barely audible.I am alright with soldering and double checked my connection , they seem alright.Though even if i do not connect the mic capsule, to the pcb, there is same hum coming out of it.I am sharing the link with you guys/gals.please let me know how can I fix this ? what am I missing ?I am also sharing the picture of the recorded hum, my interface is ssl2, and its working just fine with other condenser and dynamic microphones with the same mic cable.I appreciate any help/tips/guidance.
Mic capsule :
https://www.aliexpress.com/item/1005002270133707.html?spm=a2g0s.imconversation.0.0.3afa3e5fgz3zFjMic PCB:
https://www.aliexpress.com/item/400...16972449738933004e173b!10000010451202052!im!!

 

[MagnetoSound]

Is the body well grounded?

 

[khalidgul]

thanks for the quick reply.yes, the body was well grounded.so the ground pin is connected to the body.regardless is causes the same hum.though when i touch the negative terminal of the mic capsule terminal, the noise goes away, its not just touch, i have to press a little.I double checked the soldering its just fine.no part is poorly soldered or disconnected.

 

[JW]

You've assembled the mic all the way, right? Like, headbasket, and body sleeve on?

 

[Khron]

Would be interesting to know how the circuit on that board actually looks like...

The components, especially those fat capacitors, look suspiciously "symmetrical". But that thing was most definitely NOT worth 60-80 bucks

 

[Drosselmeier]

I think the noise is due to the fact that these parts (marked with red) are soldered onto the PCB

 

[khalidgul]

Thank you guys for the feedback, well, I improved the grounding.it turned out, that I did not ground of the basket/shell of the mic to mic pin 1/ground.As I connected, it started working just fine. thanks is there any body who can help me explain the circuitary of the board.will appreciate greatly

Is the body well grounded?

.

 

[khalidgul]

Would be interesting to know how the circuit on that board actually looks like...

The components, especially those fat capacitors, look suspiciously "symmetrical". But that thing was most definitely NOT worth 60-80 bucks

thank you.i am interested to understand your insight.if you are interested to to knopw more.please let me know what can i share with you.

 

[Khron]

please let me know what can i share with you.

Well-lit, well-focused photos of the top AND bottom of the board, as well as whatever markings are on the flat side of each of the two small 3-legged transistors.

 

[MicMaven]

turned out, that I did not ground of the basket/shell of the mic to mic pin 1/ground.

Good to hear you solved the problem. I have been in that same position often enough, myself.

Sidebar Comment - I have found some head baskets and bodies are painted or coated inside with some sort of paint or clear-coat and this prevents a good ground all the way along the body shell and basket. I often scrape through such material in various places inside the microphone to assure there is good continuity from end to end, as well as to pin 1 on the XLR connector. I sometimes connect pin 1 on the XLR connector to the tab above and between pins 1 and 2 to further assure bonding pin 1 to the XLR connector shell. A feller named Jim Brown (ham radio call K9YC) has published a number of articles on what he calls the "Pin 1 Problem" on a website. Search for his name and call sign to find a treasure trove of info on this.​

​

Similarly, I sometimes open DC power supplies and scrape off paint inside their cabinets to assure good grounding - and I do that with various project boxes I use to make accessories for my radio station to assure good grounding continuity between the circuit and the cabinet.​

Of course, I acknowledge I may be telling you something you already know, but that is just my take on the matter. My road to Heck is well paved with all of my good intentions! Happy trails to you. James /K8JHR

 

[MicMaven]

. But that thing was most definitely NOT worth 60-80 bucks

Whew ... I figured as much without knowing for sure. I considered those boards multiple times, yet stepped away, opting for either much less expensive boards (risking less cash in case of a dud) or trying Jules Rykenbush's Alice OPA boards. It is so hard for the novice builder to know what is true and what is marketing bushwah. I appreciate the assistance I get here.

Parenthetically, I once tried a different board by that same manufacturer, TZT, and several list members expressed uncertainty about it! It sounded OK for my limited purposes, but it was not particulary well made and I experimented with it often as a learning platform, eventually futzing a trace carelessly with my soldering station, rendering it office art.

James

 

[khalidgul]

Update:
I was able to fix the hum and buzz by adding two capacitors(layered ceramic 100nf) connected from pin 2 to ground and pin 3 to ground.It is not entirely removed, still there is a bit around -40db, but the out put is useful for average use.I am attaching recorded sample.I am interested to learn your feedback on sound quality.I used low cut filter around 80Hz to remove hum buzzz.it additionally cleaned the voice.I am planning to further change the input capacitors with the polystyrine silver film capacitors.lets see if they make any difference.There are already installed stacked film PET capacitors. there is jumper which help select tone, one with slight top end one with neutral.capacitor values are 1nf and 100nf.
https://www.google.com/imgres?imgur...2ahUKEwjRruGHn6SCAxVumicCHc_yBxsQMygRegQIARBzAny insight on improving the setup is appreciated.Its an educational activity.Thank you very much indeed.