Tonearm hum only when stylus is on record?

Tonearm hum only when stylus is on record?

Postby Vear » Wed Nov 13, 2019 12:57 pm

My JMW9 tonearm is quiet when it is lifted off a record, there is no hum even when I touch it and I have continuity to the ground lug. But when it is resting on a record (whether motor is on or off - even unplugged) I get a low level hum. The hum is faint but it is definitely there and my other turntable does not do it with the same gear and cartridges. I have tried three different cartridges with the same result. I've tried everything I could think of with no luck.

Any ideas what could be causing this?
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Re: Tonearm hum only when stylus is on record?

Postby Vear » Thu Nov 14, 2019 12:28 am

Well it looks like I got it! After months of hunting and narrowing down the issue it's ironic that the day I post the question here I figure it out...

So a little background. When I got this table I noticed that I was getting a hum only when the needle was on the record. It didn't take long to realize that this table had to be well isolated. It was picking up vibrations from from the A/C compressor outside. Some additional isolation and it was much better but not completely silent. I figured that it was because the table was not on my better, more solid rack.

I recently switched the position of my turntables and noticed that the VPI still had a low level hum. What the heck! I tried everything, cables, cleaning the spike and female cup, adding additional ground wires, testing my cartridges with a DMM, cleaning the lemo connections, turning off all nearby appliances and lights, shutting off breakers, removing any other electronics from the line, you name it- I tried it. It was really starting to bother me and I was determined to get to the bottom of it even if it meant taking the table to VPI. I was really starting to think that there was a problem with my tonearm.

Then today it dawned on me that the only other appliance I had on today was the amp itself which was below the table on the main rack. Sure enough when I isolated the feet of the amp from the shelf it was resting on and the hum was gone. Apparently the stylus was picking up the tiny imperceptible vibrations from the two transformers in the amp (one EI core and one toroidal- both well shielded). Crazy huh? This was literally the last thing I thought of. I'm thrilled that I finally got this tonearm to be completely silent.

So, since I thought I had isolated all of the obvious potential external mechanical noise I ended up chasing my tail hunting for an electrical noise that I thought had to be creating the remaining low level hum. It turns out that it was also mechanical and right under my nose. I had considered the possibility of EMF from the amp but never did I consider the otherwise imperceptible vibrations it may be emitting.

While the isolation from external vibrations on VPI's may not be their strongest suit, I think this shows (at least to me) how resolving their uni-pivot can be.

I thought I'd post this just in case someone else has a tonearm hum issue that has them chasing their tails looking for a ground loop. Don't rule out the tiny vibrations in your home that the stylus on a uni-pivot can detect. While properly isolating these tables can be a pain- in my view, that ultra sensitivity of the Uni-pivot is a good thing because that means that it won't miss any minute vibrations when it's in the grooves either...
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Re: Tonearm hum only when stylus is on record?

Postby Brf » Thu Nov 14, 2019 9:20 am

Great post and thanks for circling back with an update!
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Re: Tonearm hum only when stylus is on record?

Postby seamonster » Thu Nov 14, 2019 10:51 am

+1 what brf wrote. I've got my table on a wall-mounted shelf, which helps isolate.
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Re: Tonearm hum only when stylus is on record?

Postby miner » Mon Nov 25, 2019 1:29 pm

Return solutions are always a benefit to someone else down the road
McIntosh C2300 pre; McIntosh MC452 amp; McIntosh MCD500 SACD; VPI Aries 3 with 3D arm and Ort. Cadenza Black MC cartridge; Manley Chinook SE; PS Audio P5 reg.; VPI SDS; Pioneer RT707 R2R; Nakamichi ZX-7 cass.; Sf Electa Amator III; Sf Gravis II sub
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Re: Tonearm hum only when stylus is on record?

Postby Mr_Putty » Mon Nov 25, 2019 10:22 pm

I circled my tail a lot over the last year. My Prime motor had obvious vibrations I did not like. As it ran-in and became smoother I focused on other sources of vibration. My system components sit on a very solid (reinforced) oak desk and each component has its own shelf. The desk is on moving dollies and my floor is tiled on a slab. One of the best improvements I made was adding several snug fitting wood blocks between the floor and the bottom of the desk. This stabilized the front to back vibrations I did not know I had. To move the system the blocks are removed so the dollies again get the full weight of the desk. Most components have two layers of suspension. A layer of granite base on a wood plank. The TT has a wood plank and then two granite layers. I made an effort to isolate the stone and wood planks everywhere. This setup was very cheap and is working quite well. The TT motor can be suspended off the wood plank and that may yield even more isolation. I do not know what this will do to wow and flutter. But I’m hopeful nothing negative. I’m also using a variation of Votan’s original tweak, and a second support under the 3D arm. I am truly amazed at how good/great some of the older records I have sound. And direct-to-disc records are a true delight. I wonder where my system will be in another year? This a GREAT forum that VPI has allowed us to use and benefit from. Thanks to Brf and everyone else that contributes. Lets keep it going!!! :D
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Re: Tonearm hum only when stylus is on record?

Postby Dorian » Tue Nov 26, 2019 12:36 am

Thanks for taking the time to write up your solution Vear. I’m sure many people will benefit from it in the future.
VPI Prime #959 & Outer Ring| SoundSmith MIMC Star | Herron VTPH-2A | Primaluna DiaLogue Premium HP Integrated | KEF LS-50s | SOTA Condor & Roadrunner | Audio Sensibility Cables | Symposium Ultra | AQ Niagara 1000 | Stillpoints LPI | Focal Clear
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