Active xlr - Problem

[Shamadan]

Hello
I've built johnk active xlr but it doesnt work properly. I have huge "ocean" sound with my signal. The noise is always there even when i turn off power supply.

Without any doubts i made a mistake but can't trace it. First I want to make sure which layout should I use. There are tiny differences between those layouts.

On smaller layout 1u cap is connected to pin 1 of TL72
also resistance between Xlr2-Xl3 is 6.8 or 13.6 kohm

Any help would be appreciated

 

[Shamadan]

Hi I've found a schematic that was propobly used to make these layouts.


I am puzzled. I have get rid of this ocean noise with 22 uF bipolar capacitors.
One issue remain. Huge noise floor
Volteges looks ok when i follow schematic connections.

1 9V  8 18v
2 9V  7 9V
3 9V  6 9V
4 0V  5 9V

It sounds like the noise floor have been amplified What should I look for to fix noise problem ( I've spent 8h debugging this veryfied layout)

[Shamadan]

Hi. Sorry to bother You again but this simple circuit is getting on my nerves.

I did an audio-probe test and I don't understand what is going on.

There is a huge noise after 22uF capacitor from leg 7
There is a smaller noise after 22uF capacitor from leg 1
There is no noise before those capacitors

Looking at the schematic there are only 2 resistors and xlr pins after these caps. So i thought that noises may be connected to the capacitors I used, so I swap  them with non-polarized 1uF but it didn't change anything. I removed caps from board and there was no noise on 100 ohm R6 and R7.
Bipolar caps that I used were done from 2 normal electrolytic caps connected  - to - sides.
Do I need to buy proper bipolar caps or should I look for something else.

Any Ideas what else should I check  (I tested for shorts like 100 times)
Thanks

[Freppo]

I did my own layout from the same schematic, but a phantom-powered only version.
It's a good circuit and should be noise free. Sorry to hear you are having problems.

Have you tested to swap out the IC?
Sound strange though that you still have the noise even if disconnecting power.
I would check the cuts and double links again.

If debugging takes more then one hour I usually build from scratch..
At least small easy layouts such as this one. I have no patience :P

/ Fredrik

[Shamadan]

Thanks Fredrik for confirming schematic.
First I made layouts from johnk than remade it to match schematic. Unfortunatly no sucess.
I would have built a new one but I made it on one board with condor speaker simulator. (both layouts are separate).  I would give it a try again  in a few days.

[Beaker]

Hi there, sorry that this is giving you grief.

It would be useful to us, if you could post two photographs of you your board - one of the component side, and another of the solder side.  

Someone may be able to spot a mistake, that you have missed.

[Shamadan]

Thanks
Images would be kinda hard to read. Now everything (exept one mistake) is according to schematic. I know that ground is somehow amplified with the signal. It sounds like white noise and is exactly  as loud as signal from guitar. Thanks. Will let You know when  i crack it :-)

[Beaker]

You would be suprised - we can often spot issues from photographs.

[Shamadan]

Hi. Finally after many hours i found my problem and .........
Surprise, surprise active xlr was ok. The freaking noise come from power supply. I powerd it from 12v ac to Diode bridge and then a booster.
I was planning to use this setup with 5ac winding inside my tube amp, but now I know it wont work properly..

Can you recommend how to obtain quiet power supply from 5V AC to 18V DC.
Thanks for all your help.

Btw.  You would find my mistake within few seconds, but now I learnt important lesson. I wasn't aware that so much noise can come from power supply.