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RF Interferenece and hum on tonearm

As much as I enjoy NPR, I'm having a hard time enjoying it when I use my Denon DP 75 DD turntable, Lustre GST1, and Grado Signature Platinum cartridge. I am running three grounds from the TT system to the preamp:tonearm shield, TT motor, tonearm mounting. The RF only occurs at moderate to high volumes and increases dramatically if I touch the tonearm wand. Touching any other part of the tonearm does not increase the noise.

In addition to the RF interference, I have a hum problem.

The CD player and TT are plugged into an APC power filter. The hum decreased as I added the ground wires. Unplugging the CD, plugging the TT directly into the wall, moving the wires did not change the hum or RF. Moving the tonearm closer to the motor increases th
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swampwalker's avatar
swampwalker
5,138 posts
 
Do you have another cart you can swap in? Grados are known as being particularly sensitive to picking up noise and hum.
hifihvn
943 posts
 
It sounds like the tonearm ground has a poor, or broken connection somewhere, is the most likely thing I can think of.Try wrapping some soft wire strands (after stripping 2-3 inches of insulation off it)around the arm, with enough length of wire to ground the other end. Some flexible light gauge stranded wire. Maybe just tape over the strands of wire on the arm wand so it doesn't cause any scratches on it. If this works, that would verify that there may be a poor connection on the arm ground, maybe where its out of sight.
hifihvn
943 posts
 
Swampwalker was posting while I was, and got his in first. I forgot about Grado having this problem, but it still could be the ground for the arm.
hifihvn
943 posts
 
Also, if your arm has a "SME" type of plug in headshell, maybe try running a ground from the cartridge leads ground wires, maybe off of a clip ground to the metal headshell, if it is metal, otherwise this idea wouldn't do anything. If it does work, double check to make sure you don't loose anything sonically. There are different kinds of grounding schemes used in some arms. I've seem some use a separate shield over the lead wires going through the arm. This was done in metal arms too, not just non-metallic arms. Also a little metal foil in between the headshell and cartridge, grounded to to cartridge ground, if the headshell is non-metallic.
hifihvn
943 posts
 
Also, if your arm has a "SME" type of plug in headshell, maybe try running a ground from the cartridge leads ground wires, maybe off of a clip ground to the metal headshell, if it is metal
This may also work for any metal of head mount, as long as it is metal, and bonded/connected to the metal arm wand.
stringreen's avatar
stringreen
6,470 posts
 
Replace your cartridge. Grados can work in the right system...evidently you don't have one of those.
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