Two mic input transformers in MU metal case. One is MORE sensitive to 180hz hum?

Simple test setup. Swapping transformers around.  All else same. One transformer seems more sensitive to picking up 180hz hum from power supply transformer.

Is this a common, known thing?

Are they both the same exact type?

Cheers

Ian

Yes, all else same.

But i think I found the issue. They are in a MU Metal screening can. They are at different internal angles.

What about 60Hz or 120Hz - are those frequencies not measureable?

mkiijam said:

Simple test setup. Swapping transformers around.  All else same. One transformer seems more sensitive to picking up 180hz hum from power supply transformer.

Is this a common, known thing?

Click to expand...

mu metal is commonly used magnetic shielding.

I recall well into last century when I was trying to source chinese mic transformers for use in inexpensive install (background) music systems. At first the chinese vendors didn't grok what mu metal was, but they finally figured it out because money talks.  8)

Inside these install powered mixers that had 70V/100V audio output transformers for driving constant voltage speaker systems. Hum wasn't the biggest demon, it was magnetic coupling from the output transformer to the mic input transformer causing instability.  ??? One low power amp was only a few watts so small and these transformers could only be spaced inches apart.

JR

mkiijam said:

Simple test setup. Swapping transformers around.  All else same. One transformer seems more sensitive to picking up 180hz hum from power supply transformer.

Is this a common, known thing?

Click to expand...

Even if construction was absolutely identical, Mu-metal can loose some of its properties with heat, stress and shock.