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50 hz hum when using MC on Rega elicit Amp

I just assembled a new Ortofon Rondo red on my Rega Planar 3 TT.
It still need a run in but man...even now... what a mind blowing sound !!!!!
Apparently my 20 years old Rega Elicit kicks ass even in its MC input.

There is however a small issue with about 50hz hum I get.

The following facts might help troubleshooting:
1) I use an MC cartridge for the first time.
There were no such noise issues when I used an MM cartridge.
2) I hear the noise only when the interconnect of the Planar 3 is plugged in so one could think that it comes from the head... but.... could it be an MC phono stage issue that is revealed only when there is load on its input ?
3) Grounding is fine and I measured 1ohm from the RB300 bare metal to the end of the ground cable.
triskadecaphobic
triskadecaphobic OP
81 posts
 
Marakanetz,

Here are 2 images:
1. A picture of the board (the right side of the picture is the phono stage)
2. A drawing of the board.

https://picasaweb.google.com/100352153551466589742/January29201302

After viewing the drawing, do you still think that there are caps related to DC regulation that might only affect the high amplification needed for MC cartridge ?
With MM cartridge I have no hum problem.
triskadecaphobic OP
81 posts
 
Marakanetz,
I thought about it and I don't think it's a problem with the caps in the phonostage DC regulator due to 2 reasons :
1. I replaced them 3 years ago.
2. If this was a regulation issue related to caps, the hum would be present all the time. In my case it is present only when the TT is plugged in.
This means that it comes from the TT. Most likely a grounding issue but since I measured continuity between the bare metal of the arm to the amp ground I don't know what causes the hum...
Please advise.
triskadecaphobic OP
81 posts
 
More valuable info that might support the claim that the hum comes from the TT:
When I disconnect the small connectors of the cartridge, the hum is gone.
I verified continuity of all 4 wires:
1. Red to + right
2. Green to - right
3. White to + left
4. Blue to - left

All are ~ 1 ohm.

Why is the cartridge producing this hum then ?
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