Tube Preamp noise issues

[craigmillard]

Hi guys,

What do you think this noise is?? Starts at about 0.20 seconds

https://www.dropbox.com/sh/9zhm1mjpmj1s7lg/AABDm_-SrWODO23Y8T7NSx-ua?dl=0

Its a high gain tube preamp based on the uberschall with a max1771 smps. I have used this layout and smps with a jcm800 preamp clone without this issue!?

It starts of quite strong then fades into the background a bit more.. I can only think smps noise is getting through the filtering but why does it not start straight away? Always take a while before it kicks in!

Any thoughts would be much appreciated!!

Cheers guys

[J0K3RX]

Microphonic tube..  swap the tubes around and make sure they are seated real good.

[craigmillard]

Thanks Jok3rx i gave it a go but no dice.
I actually changed the valves for a known working set and they are held in with valve retainers so they are a tight fit!
Still the same strange noise!

[craigmillard]

Found it! The inductor was the wrong way round! Didn't think it mattered but obviously does! Is this due to the magnetic field being constrained more if you start on the inner winding!? I'm using murata inductors and they have a dot to indicate where the innermost wire starts!

[J0K3RX]

Dunno man... That's a new one on me! I have built quite few now and have not had anything like that.. Really glad you figured it out though so I will have an idea of what it is when/if I hear that in one of my builds! Valuable info, thanks for the share! Now how's about sharin that Uber?! 

[craigmillard]

Still tweaking it:) but will share once complete! Sounds pretty badass at the moment though! Not quite enough treble for my liking! Thanks for the suggestion earlier, was just about to give up!!