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Lindell 503 Hum Fix
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
Old 24th June 2016
  #2
Thanks. I may try this. My 503 has been quite a bit of trouble. So noisy it is un usable for acoustic instruments on slots 2 and 3. My bushings also crumbled where you secure the modules.
Old 24th June 2016
  #3
Quote:
Originally Posted by achase4u View Post
Thanks. I may try this. My 503 has been quite a bit of trouble. So noisy it is un usable for acoustic instruments on slots 2 and 3. My bushings also crumbled where you secure the modules.
The MuMetal has been great and my rack is now dead silent. Just like the previous poster, I used electrical tape so that the metal doesn't short out any connections it touches on the side that is closest to the slots. As far as your bushings goes...that suuuuucks. I wish you the best of luck in getting your Lindell up to snuff. If you have any questions or find any answers, please post so that it can benefit future Lindell owners.
Old 24th June 2016
  #4
Lives for gear
 

Interesting. My biz partner just gave a little 3 slot Lindell rack with one each of the modules. Haven't plugged it in yet but I'll be curious about the noise.
Old 24th June 2016
  #5
Quote:
Originally Posted by kslight View Post
Interesting. My biz partner just gave a little 3 slot Lindell rack with one each of the modules. Haven't plugged it in yet but I'll be curious about the noise.
Congrats on the new rack! I love 500 series stuff. Throw a mic preamp in the slot closest to the IEC inlet and you will see what we mean. Definitely pick up some MuMetal from eBay, you'll need it.
Old 24th June 2016
  #6
Quote:
Originally Posted by justinheronmusic View Post
The MuMetal has been great and my rack is now dead silent. Just like the previous poster, I used electrical tape so that the metal doesn't short out any connections it touches on the side that is closest to the slots. As far as your bushings goes...that suuuuucks. I wish you the best of luck in getting your Lindell up to snuff. If you have any questions or find any answers, please post so that it can benefit future Lindell owners.
Thank you. I certainly will. I actually cracked it open today to see how it is made(I have experience in manufacturing)

It's not really that good, I am afraid. I was a bit apalled at the solder joints. Many, many cold ones and some with [I]holes[I]in them... which is not good. I resoldered the entire pin mother board and will be inspecting further. Soldering gets an F. I took some pics and will post perhaps in another thread.

I will try the mu-metal. Honestly, with all the issues I've had with the box(it has already been repaired by a dealer once for LOUD hum issues) and now seeing the solder - I couldn't, with good conscience, sell this to someone. My only option would be to chuck it. So I figure I will try this mu-metal fix, trying to separate all the xlr components from the power components close by.

As for the bushing - yes, that sucks. Very cheap metal. Part of the problem is using an adapter bushing or conversion insert at all in a situation like this. Truly, the rack should be directly tapped for mounting screws. Instead, they used a larger tap into which they inserted a dual-threaded bushing. Male outside to fit the chassis, then female inside to take 4-40 mounting screws for the module. They did NOT secure the threaded inserts at all. A little nail polish or even some semi-permanent thread-lock would really be proper. So what happened to me is that I went to unscrew a unit one day, and the insert came out instead of the module screw. So the module faceplate was sandwiched between the insert and screws. I had to manually remove the insert and try to put it back in the chassis which is when it crumbled.

I've only swapped modules 5 times in this thing I would think. I barely used it after the first noise incident since I don't have time for faulty gear when I am trying to record. So it really didn't last long.

I have taken some JB weld and filled the chassis where the insert would go. I will let it harden and drill/tap it and hope to limp along on that fix, IF I can solve the noise issue...

My GS review of the chassis here Lindell Audio 503 Power
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