U67 IOAUDIO build sounds like im recording outside in a storm

mica · Mar 24, 2018

Is it a loose connection or the tube maybe? Got the tube from Christian Whitmore. Supposed to be real quiet. The B+ is 210V just checked it.

Need help where to look for errors :'(

Noise:
http://soundz.dk/noiseu67.mp3

EDIT: Tried a different tube. Same noise..

Studio Mollan · Mar 24, 2018

Make sure all the connections in the hi impedance area are cleaned thoroughly. It might be a tare in the capsule membrane, but that would probably not make a constant noice like that unless theres a very obvious tare in the membrane. Also make sure all the connections to the capsule is secure.
I had an issue like this with my u67 builds and all noise went away after i cleaned the solder joints.

mica · Mar 25, 2018

The capsule is looking totally mint. No issues there. I tried resoldering some points and giving it a good clean, but still noise..

RuudNL · Mar 25, 2018

A simple way of checking this, is to disconnect the capsule and connect a capacitor (82 pF) between the grid of the tube and ground. If the noise is still there, you can eliminate the capsule.

mica · Mar 25, 2018

I have another capsule i could try, but the one in there now is a brand new TSKguy U67 capsule.. Why could it be the capsule making that kind of noise? Just curious..

RuudNL · Mar 25, 2018

Any leak current in a High-Z circuit will produce this kind of noise.
The fact that a capsule is new doesn't really say anything.

Nyquist · Apr 2, 2018

Try re flowing the capsule wiring to the PCB. I've had similar noise before and found a dodgy connection was the culprit.

tskguy · Apr 4, 2018

Also, if you find out its a capsule issue I am very happy to make sure its good..

mica · Apr 17, 2018

It turned out to be a PSU issue feeding the tube too high voltage (heater) Took it to a local studio guru / repairguy. The 100$ NOS Mullard tube from Christian Whitmore was damaged and making the noise

But its fixed now (heater back at -6.2V) with a new (cheaper) tube and sounding lovely with no noise!

And thank you Eric for chiming in. Its one of your capsules in the build

Khron · Apr 17, 2018

First rule of troubleshooting (electronics) - thou shalt measure voltages :

mica · Apr 17, 2018

Haha yes i know.. I was embarrassed to write it just now, because it was such a dumb mistake, but maybe it could help others searching for similar issues..

Khron · Apr 17, 2018

Learning from mistakes is indeed one of the best lessons. But, of course, it's easier and/or less painful(?) if you can learn from others' mistakes - we've all been there ;D

tskguy · Apr 19, 2018

Happy to hear it's all good!!

U67 IOAUDIO build sounds like im recording outside in a storm

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