OP, read your post and I have experienced a similar issue (and commented on it before) with TT/LOMC and hum/hiss in background. I know how frustrating this was for me, and feel your pain. 

My problem was caused by my wireless router and likely poor insulation on my ethernet cable to my streamer.  I was at the same height and about 6 ft away from my TT.  When I disconnected and it totally, the hum went away.  I relocate the unit to the floor about 20 ft and haven't looked back.    

If someone has already mentioned this as a possible fix, my apologies for not reading through the posts. 

If all else fails, get a Radial Engineering J-ISO or similar.  basically a 1:1 transformer for audio signal and it will at least prove whether it's possible to eliminate the hum.  I've used mine at various points in the signal path for troubleshooting

I upgraded from these a couple years ago but haven't really heard a difference--may be my hearing or may not but these are very low capacitance (essential for phono cables) and in your budget--i think Belden makes them for BJ:

I had a persistent 'hmmm' for a time that drove me sane....

And, as noted, a funky cable not grounding well.

Took persistence to track it down, and the obviousness of it... 🤦‍♂️😏

Glad you were able to find yours.... 👍👌

etbaby, I don't think an isolation transformer would solve the OP's actual problem, since the short in the ground connection occurs AFTER where the ISO Max transformer would be inserted, between the AC source and the power cords. He had an interruption in audio ground.

The hum problem is an issue that occurs in most professional music areas. The solution is to install ISO Max transformers. It will cost you about $200 but will solve any of your hum problems.

@adamsrpm  I'm brand new here and I thoroughly enjoyed your post and am so glad your problem is fixed! ✌️ I'm learning so much in the forums. Thanks everyone. 😀

I had a Revox linear tracking TT with a persistent hum issue.  Because of very limited space in which to relocate it, I got this item on Amazon:

Electriduct 1/2" Tinned Copper Metal Braid Sleeving Flexible EMI RFI Shielding Wire Mesh (0.32" Diameter) - 25 Feet

It's a braided metal sleeve that you can slip over the IC.  it ended up solving the hum issue...at least in my case.

The tonearm is a Technics with removable headshell.

The problem was solved by changing the phono cable, which was a left/right channel and ground all within one assembly, with the stock cable and ground wire that came with the turntable. The stock cable eliminated the hum. I had tried cheater plugs on the turntable, phono preamp, and control preamp in various combinations. My non-scientific conclusion is the phono cable was the cause! Thank you for all the input and I have increased my budget to $200+ for new cable and will make sure they are returnable.

Sounds like tonearm wiring. Is it continuous wire, or are the cartridge leads soldered onto the arm?

As to a cable upgrade Grover Huffman cables are well built and very reasonable

You may have to go a bit above $100 but he does quality work

I doubt it’s the power cord.  On something as sensitive as your phono cable, I’d take a volt/ohm meter check it out. Who knows, maybe it was just a loose or dirty connection.

All the best.

Am I missing something? We do know the cause of this problem, and it’s been cured. Yes? A defective IC. 

Now that you know the hum originated in the cable, start trying various cables from vendors with 100% refund return policies. When you get one you like with no hum that also sounds good, you’re done. Enjoy the music!

I would try Audioquest, Morrow, Pine Tree Audio, Kimber, etc.

Do you have a digital processor? If so, that likely is the issue. It was for me. Drove me batty until I figured it out....Use  a cheater plug on the power cable and that will be the end of the hum. Amazon also sells a hum manager plug but it costs $87. But it too works. 

You could try cheater plugs elsewhere too.

Hire another exorcist.

Put the phono stage and preamp on ground cheaters. 

+1 @speedthrills ​​​​@lewm  these sound reasonable possibilities. In addition to tonearm wiring @russ69 . Turntables can be maddening contributors of hum. I’m dealing with an issue right now on a vintage Thorens where by it only hums in the cue up position; after the record is played. 

In my case, the hum increased with a higher gain setting. On my phono preamp  the choices are 40, 50 and 60. The MC cartridge that I have has a lower output than my MM, thus needing more gain. When I would switch the gain, the hum increased

Congratulations to the OP on solving the problem.  I am going to commit audiophile heresy and suggest that he leave well enough alone and go with the stock cables.  Perhaps he can do research into the company that makes the stock cables and see if they offer higher end cables that use the same basic design.

  I am curious as to why the hum is worse with mc cartridges.

Yes, I did connect the turntable directly to the Parasound P 6 with the same result. When going back to the turntable's stock cables, the hum stopped. Now I need to find some quality phono cables that don't cause a hum

Any suggestions for a phono cable at $100 level?

I noticed you're using the same preamp I have (Parasound P6).  I have likely missed other messages prior to those I just scanned.  Tell me, did you try simply using the phono stage in the P6 rather than your separate phono amp?  No compelling reason to I suppose but that's likely an easy check.

I have no reason to be optimistic but the head shell comment may have merit.

Best of luck.

More to the point, you might contact Pangea or your vendor and ask for a return authorization, on the basis that their ICs seem to have an internal short circuit on the ground side. By "internal" I mean that the issue probably is inside the insulating sheath or outer cover OR it's at one end where the wire is soldered to the ground side of an RCA plug. (It's unlikely to have been a problem with an AC cord; in that case you would have no power to the TT.)

If your telecommunication provider is coax cable based, this 4k compatible filter and available at Amazon.ca, could be the end of your nightmare.Works perfectly for me : 

Isolation Transformer / Ground Loop Isolator https://a.co/d/dAvbDC1

Your cartridge is acting like a microphone and if its MC then its being amplified much more by your phono pre-amp than if it were a MM. Move your turntable further away from your system and the hum will reduce. Also, move your RCA cables from the TT away from any other cables including AC power cords. 

Sometimes a professional with a multi-meter and an oscilloscope is the best answer.  It's okay to admit, i have a son that's too busy doing this stuff because of people like me. 

Just because it has to be said, and I don't believe that anyone else threw this out there, it could be a Dinah-Moe-Humm.  If so, contact Frank Zappa.  I laugh deeply now, as a totally nerded Zappa fan. 

So now figure out the difference between the cables that work and the ones that don't.  Probably in the way they are grounded.  And then you can order upgraded cables that don't hum.

Audio envy has offered cables with versatile grounding systems and I think they are pretty good at customer support.   Other cable makers are too.

Congrats.

Jerry

I dug-out the cheap cables that came with the turntable--including the power cable. Replaced the Pangea Audio phono cable and power cable. NO MORE HUM!!

I can't beleive it. Even at the highest gain setting--no hum. The phono cartridge is a Zu/DL-103 Mk.II. Everything sounds great, now.  Thank you to all who weighed-in on my problem.

Also, you haven’t ruled out an internal break in an IC wire, most likely the phono cable but could be elsewhere, that interrupts grounding. To check that just insert some cheap alternative ICs in place of what you’re now using. For one, try the Sony supplied phono

cable. Like Russ suggested also check cartridge pins, internal tonearm wires, and joint between headshell and arm wand. Is it tight?

Is this a new problem, or did this setup previously work ok? What phono cartridge are you using? Can you hear the hum when the music is playing?

I have tried movig the ground wires using one from the turntable to both preamps and just one or the other preamp or no ground at all. I have been using an upgraded interconnect cable (Pangea turntable cables with integrated ground wire) and not the one that came with the turntable. The turntable is a Technics SL-100C (essencially the same as the SL-1500 without the built-in preamp). I can hear a sound if I tap on the on the tonearm...maybe there is something wrong there. My control preamp is a Parasound Halo P 6 and the phono preamp is a Parasound JC3 JR. I realize I have budget gear, but I don't think that's the problem. I appreciate the input. Thank you.

Russ’s guess is as good as mine. You’ve eliminated most other options.

I just purchases a Technics 1200G as a second table. I had a hum issue on the right side only. After trying all the same cures you used and a few more with zero effect. I bought AT headshell remounted cartridge ,now its dead silent !  If you can switch head shells that might be you answer. 

Are you grounded from your turntable to the stand-alone phono preamp? Do you move the ground back and forth from your stand-alone phono pre to your control preamp? If yes, I would guess a wiring issue in your tonearm. 

Could there be a broken ground connection inside the jacket of one of your ICs?