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Old 21st December 2015
  #1
Lightbulb Lindell 503 Hum Fix

After purchasing a RND 511, and filling the 3rd and last slot in my Lindell 503 chassis, I plugged a Rode NT55 into each preamp and did a shootout. All was well. I then switched to a Sennheiser E906, and from slot 1 to 3 there was increasingly more noise. The 511 had a pretty loud hum from about 30z all the way up to 250hz. Slot 1 is dead silent. Slot 2 had some hiss (which I thought was entirely the preamp). Slot 3 had a crazy hum that sounded like a bad ground, and was unsuitable for recording.

I ordered some MuMetal from eBay, which was $26 for a single 8x10" sheet. This was enough to form a multi layer cover over the area where the cord plugs in from the wall, as well as the PCB board for the power supply.

The RND 511 in slot 3 is still buzzy without anything plugged in, but once a mic is plugged in it's dead silent. No noise whatsoever for all 3 mic preamps.

A fellow GS member recommended the mod, and I just wanted to post this so that everyone knows that Lindell chassis hum like crazy the closer the mic preamp is to the power supply, and also that there is an inexpensive fix for it.

Original post:
https://www.gearslutz.com/board/11184982-post18.html