Fathead ribbons and EMI

[Chinagraf]

I have a pair of fatheads with Lundahl trannies, and I use them mainly for drum room out in our foyer, but when I use them as overheads in my smaller booth I get hum in the one on the left side of the room. If I swap mics it's still in whichever one is on the left side of the room. If I take the mic just outside my door into the foyer the hum goes.
Is there anything anyone knows that can be done to shield them more? I've looked everywhere for the source for the hum, turned off all the light, switched off printers upstairs, everything I can find but nothing gets rid of it. Could it be power cables going through the wall? Aliens in our basement? Should I just give up on using them as overs in my booth?

[Drumstruck]

They're just incompatible with that location Andy - there's no hope of a fix - you'd better send them to me

[rick]

You could try adding copper shielding inside around the two wires that
Lead from the ribbon to the trannie and make sure the case is the electrical ground
With a multimeter ( the grill may be painted or something dumb making it useless as a shield)

But really it's not unusual for some ribbons to pick up hum
It's all about case shielding design versus sound ( tone)
Did you rip out the interior grill ala jolt mods ?
There goes the effective shield etc

[Chinagraf]

No, left the grill in just replaced the trannies, kept the wires from the motor to the tranny as short as possible. I managed to get the trannies in the casing the original ones fit in, but it aint mu metal by the look of it, more likely stainless. It's definitely location dependent. The only place it happens is in the booth directly above the kit. I've swapped the overhead with my Milab and put the ribbons in the corners of the booth down by the floor and they are quiet as.
Would active ribbons be quiet, or is the motor to the tranny run that picks up the gunk in the air?

[rick]

It's the ribbon motor and the wiring itself
It's job is to make noise if it moves ...
Guess what ? It works !

[Chinagraf]

Hooray!

[Chris H]

.....this suggestion may reveal the extensive limitation of my tech savvy, but could twisting the wires help...... if they arn't already twisted?

[Ben M]

Could you use a voltage detector (AC detecting wand) to try and pinpoint any interference above your mic in the ceiling or wall... maybe a crazy idea?

Warning: May lead to many trips to Bunnings

[Chinagraf]

They don't like me hanging out alone at the studio at night playing with my wand.
Necessity being the mother etc I ended up with my Milab overhead and put the ribbons outside my booth in the foyer and ended up discovering a great position for them where the overs and close mics sound really tight in the booth and the ribbons get a great bigger room sound outside it. Kinda like the 70's meets the 80's all in one.
The Fattys are great as room mics in general.