How far is your SUT from your Phono Pre/Preamp?

Is the SUT or the phono stage in close proximity to your amplifier? Could the power transformer in the amp be the cause? Just thinking out loud....

@atmasphere  : this comes from my post: " ( an even of the SUT it self. You can rotate it for example.  ).

R.

@dhcod  : Why do you need an external SUT with your Lamm PS De Luxe? 58db plus the line preamplifier gain is enough for your 103R.

Now, in the other side : Have you in the past that kind of hum problem using your Lamm with out external SUT or made any analog rig change when you got the external SUT?

If you made any analog rig change the 103 is an easy to be contaminated and develops some kind of noise as " hum " if those cartridge/tonearm connectors are not tigth secured.

R.

Interestingly the SUT in the Lamm is a real weak point. The external, even a relatively inexpensive one like the AnaMighty one I have, is a huge improvement over the Jensen’s inside. I just A-B’d it again this morning and it sound great with the internal but the external is sublime. 
 

The system change that has caused this problem to become noticeable is a switch to SET and higher sensitivity speakers. The amp change came after I first noticed the hum so it’s not a source of the problem. 

@dhcod ​​​​​​the good news is that if the Jensen's inside the box can be quiet there is no reason an external sut cannot be too. Between grounding, and in a worst case scenario additional shielding, you should be able to get the noise down...