U47 Noise Cardioid Mode (Solved)

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JRJR

Active member
Joined
Oct 8, 2014
Messages
34
Hello Folks :)

hope you're doing well.

I have a small problem with my U47 clone. It works almost perfectly but I have some smaller problems.
There is a small hiss/hum/sirr in the sound when switched to cardioid mode. In omni mode it almost disappears (almost, it's still there but very quiet).


Do you have any ideas what the problem could be? It's based on poctop's design. (awesome!)

I guess it's something inside the PSU (bad solder point?). Or the tubes? I used WE ones.

Thank you very much in advance!


 
Dirt in the high-impedance areas might be a tiny bit more likely. That is, in case anything like white noise qualifies as "hiss" or "sirr" :)
 
Thanks Krohn, that helped a lot!

I brushed the hell out of it and now the noise in omni mode is gone completely.
But I still have this khhrchhhh when switched to cardioid.... :/

I guess the problem is somewhere outside the mic, in the cable or the psu.
Otherwise the omni mode should have some problems, too. What do you mean?

 
In my CAD Trion 8000 i discovered i'm getting some of that noise if i touch / wiggle the springy locking tab of the female XLR, where it connects to the "neck" of the mic body. Still wondering how to fix that...
 
It's getting better over time. Do the tubes need to burn in that much?

But still there is huge difference in the noise level when switched to omni...
But it is usable now.

Does anyone have an explanation for this?

Best!
 
What capsule you are using? New? Used?
Check all connections (ground especially), look for cold solder joints.
Measure voltages etc.
 
Thanks guys!
The problem solved itself. The noise just disappeared. :)
I guess the whole system needed some time to warm up...
Absolutely amazing mic!

 
This is veeeery weird.
The problem came back. I was travelling for one week, turned it on and it worked flawlessly but now the sirrrrr came back to me.
What could it be?
And I discovered something strange:

The PSU was turned off but I still had a sirrrr in the headphone until I unplugged the mic from the PSU. When I plugged it back in it came back. This seems very weird to me.

I will test new tubes soon. Maybe the capsule has a problem?
I cleaned everything up again and checkt all solder points but they all seem to be fine...

Anyone? Would really appreciate your thoughts!

 
Electrolytics in your PSU keep voltage, so they need some time to discharge.
Record that sound and put the sample here.
Maybe you have some issue with power supply?
 
Had that thought, too. But again, the noise diappears completely when switched to omni mode.
It's just there in cardioid mode. So the tubes or the power supply should actually not be the problem.
Very weird...

Can someone tell me what exactly happens when I switch the pattern?

Thank you!
 
Reverse the caapsule and change connection, then check is this still happend in cardioid pattern use.
 
Hi!

I guess I have a faulty/damaged capsule. This morning I cleaned the pcb again, checked voltages and everything and when I switched it back on I got clicks and pops out of the microphone's capsule. There is veeery small output and otherwise just the "normal" mic noise we are used to when cranking up the gain. Guess that can happen... even though I handled it very carefully.

I already ordered a Thiersch. But it will take 6-8 weeks :(
I will do the "small capacitor trick" the other day and check.
 

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Either a small capacitor, or in case you happen to have another capsule. Or at the very least, as ln76d said, connect the rear diaphragm instead of the front one.

Guessing games and suspicions won't give anyone any sort of real answers :)
 
JRJR said:
Hi!

I guess I have a faulty/damaged capsule. This morning I cleaned the pcb again, checked voltages and everything and when I switched it back on I got clicks and pops out of the microphone's capsule. There is veeery small output and otherwise just the "normal" mic noise we are used to when cranking up the gain. Guess that can happen... even though I handled it very carefully.

I already ordered a Thiersch. But it will take 6-8 weeks :(
I will do the "small capacitor trick" the other day and check.
Click to expand...

That's the spirit of DIY  :p

I ask about pictures of both sides, beacuse i think that you tested-molested the capsule alot and there's dirt/spit on the front diaphragm :)
Changing orientation of the capsule will show am i right or not.
If so, you can always clean it.
I noticed that some of chinese k47 are faulty, probably because the shim between diaphragm and backplate is to thin. With single sided k47 i swapped shims or even added another shim from the dummy side of the capsule. Then it worked without problem.

BTW - is it Thiersh reskinned chinese k47 on the picture?
After some time i realized that it's peluso capsule - am i right?
 
Is it just my imagination, or would / does that require removing the tensioning ring? And if it does, how did you retension the diaphragm? :)

ln76d said:
I noticed that some of chinese k47 are faulty, probably because the shim between diaphragm and backplate is to thin. With single sided k47 i swapped shims or even added another shim from the dummy side of the capsule. Then it worked without problem.
Click to expand...
 
Khron said:
Is it just my imagination, or would / does that require removing the tensioning ring? And if it does, how did you retension the diaphragm? :)
Click to expand...

Nope, you are right - you need to remove ring.
All the chinese capsules (and rode for example) which i worked on had glued diaphragms.
These aren't tuned with the screws, screws only hold it in place and the only thing what you can adjust is the pressing ring to the backplate.
I had only one k47 which had a little unglued  diaphragm from one side.
Then it's really hard to make the proper tension.
In fact, this capsule was not working from the start so i had full refund for it.
Someday i will send it to Mr Thiersh for reskin (for example thicker diaphragm) but right now i have M7 and M8 in line to reskin and some other priorities for money spending ;)
 
Hi guys!

you rrrrock!

I did all the tests and here is what happened:
I did the capacitor test and the noise was gone.
So indeed one side of the capsule was dirty.
I cleaned it up and now the noise is gone completely, but I still have (always had) kind of a "wind" sound when I sing into it.
It lasts for some minutes, then the mic is quiet until I sing again...
So I guess the capsule it the real problem and I will have to wait till I get my Thiersch.

Thank you all very much for your help! It's always very good not to feel alone with problems like this.
This was the first of my builds that got me major problems but now there is light at the end of the tunnel :)

Have a nice weekend everyone!

 
Congratulations :)
Did you measured polarisation voltage or overall voltages inside microphone?
Is it peluso capsule?
 
It's actually a "Vintage Microphones France" Capsule. I'm not sure if they really make it themselves. There is no homepage available. Maybe it's just a renamed Chinese K47 (looks equal).
It really feels as if the gap between the membrane and the backplate is very very thin and the membrane does not really have the right tension. When hit by a medium loud sung "p", even through a pop shield, the "wind" appears. After some time it feels as if the tension is "ok" again and it goes away.
But let's forget that faulty thing and see what Mr. Thiersch has to offer :)
The Voltages seem to be fine. 56V on the capsule and 105 for B+.

I'm already looking forward to another build. Still have to decide on a mic...

Thank you!
 
JRJR said:
It's actually a "Vintage Microphones France" Capsule. I'm not sure if they really make it themselves. There is no homepage available. Maybe it's just a renamed Chinese K47 (looks equal).
It really feels as if the gap between the membrane and the backplate is very very thin and the membrane does not really have the right tension. When hit by a medium loud sung "p", even through a pop shield, the "wind" appears. After some time it feels as if the tension is "ok" again and it goes away.
But let's forget that faulty thing and see what Mr. Thiersch has to offer :)
The Voltages seem to be fine. 56V on the capsule and 105 for B+.

I'm already looking forward to another build. Still have to decide on a mic...

Thank you!
Click to expand...

Vintage microphone, you mean Mic and mid shop?
 

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