Weird Hum Issue SOLVED

Weird Hum Issue SOLVED

Postby WntrMute » Sun Sep 23, 2018 7:38 pm

I have a TNT MK-6 with aluminum platter and it is sitting on a 150lb slab of granite supported by a machinist's stands. A great high mass stand that is spiked into my basement slab. However, I have always liked the isolation I got from those little cork/plastic coasters Home Depot and the like sell for under plants. They seem a constrained layer that costs about a buck apiece. So I stuck one under each footer and two larger ones under the dual motor pod. At the same time I made some electronic changes such as trying a different preamp and a couple of other things. Well the next day I started spinning some vinyl and noticed a hum when the stylus hit the groove. Not noticeable once the music was playing but I knew it was there. A friend came over and heard it too. He commented that he has never heard that from my system (he's over a few times a month and we are pretty familiar with each other's systems). Still the music was enjoyable and my new DIY SET 300Bs were in glorious form. I returned the system to the original form without success.

This afternoon I tried to isolate the hum. No hum with the needle in the groove but the record still. Hum as soon as the record started moving. Tried a blank record side and yup - there was the hum. I grounded the motor unit with no change. Switched the plugs where the SDS plugged into - Hum. I plugged the motor unit directly into the wall, taking the SDS out of the system, still hums. I finally popped of the drive belts so the motors would spin but the record would not - HUM! This indicated that it wasn't a recording/cartridge/amplification chain issue. Without much hope, I removed the cork/plastic spacers under the motor unit and tried one more time, - NO HUM! I have no explanation for this. I still have the little cork coasters under the footers but why this made a difference is beyond me.

Anyway, I'm back to quiet playback. I'm writing this really to reinforce the odd nature of troubleshooting hum issues. Try things that don't seem to make sense.
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Re: Weird Hum Issue SOLVED

Postby Golear » Sun Sep 23, 2018 10:28 pm

So.... if you left everything the same and then put the cork/plastic under the motor unit, will the hum return?
And then if you remove the cork/plastic, will the hum go away?

That is to say, is there a 100% correlation between the hum and the presence of the cork/plastic under the motor unit?

Is the coaster made of cork or plastic, or cork and plastic? I imagine that cork should be unaffected by electricity/magnetic fields. But there are many types of plastic and some of them could be quite affected by electricity and magnetic fields.
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Re: Weird Hum Issue SOLVED

Postby WntrMute » Mon Sep 24, 2018 6:40 am

Golear wrote:So.... if you left everything the same and then put the cork/plastic under the motor unit, will the hum return?
And then if you remove the cork/plastic, will the hum go away?

That is to say, is there a 100% correlation between the hum and the presence of the cork/plastic under the motor unit?


Is the coaster made of cork or plastic, or cork and plastic? I imagine that cork should be unaffected by electricity/magnetic fields. But there are many types of plastic and some of them could be quite affected by electricity and magnetic fields.


That's exactly what I am saying. Comes and goes with the cork under the feet of the motor pod. The fact that the same thing is under the 4 footers, which are just a few mm more outboard from the motor, seems not to bother it. This is hum picked up by the speakers - not vibration.

Something is weird here so I won't dismiss the plastic causing it but I use the very same thing under my TNT with a single motor and it works very well.
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Re: Weird Hum Issue SOLVED

Postby 930turbo » Mon Sep 24, 2018 6:33 pm

Hi WntrMute , Brf & other TNT 6 owners w/ a Classic Aluminum Platter upgrade ,

I also own a TNT 6 w/ a platter upgrade ( Classic Aluminum Platter ) . My TNT 6 originally had the acrylic platter . I installed a ground wire from the bearing well that I connected to the ground lug of my preamp of that time ( ARC SP11 MK 2 ) . I installed this wire because of my experience in my past TNT Mk 2.5 . If w/o the wire there would be severe static and hum when the turntable motor is running . With the TNT 6 I don’t know if this is necessary but I installed a ground wire as well . Here is a picture of what I did . It’s connected to the ground lug of my ARC REF Phono 2 SE .

930
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VPI TNT 6,w/Kuzma Stogi Ref 313 VTA,Benz Micro Gullwing SLR,VPI HR-X 12.7 Lyra Kleos,ARC REF5SE line stage, REF PHONO 2SE,SP10Mk2preamp,ARC REF610T monoblocks,a pair of D79B amps,EC21active electronic X over, Duntech C5000 Princess spkr,Magnepan MG3A spkr
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Re: Weird Hum Issue SOLVED

Postby WntrMute » Mon Sep 24, 2018 6:40 pm

Already have that. I drilled and tapped a hole for a similar ground wire mostly to drain static. First thing I checked when the hum appeared. I spun records all day with and without the cork spacers. Every time the hum appeared and disapeared as described. So odd.
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Re: Weird Hum Issue SOLVED

Postby Brf » Mon Sep 24, 2018 6:49 pm

I’ll have to give this phenomenon some additional thought, but right now I don’t have a clue.
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Re: Weird Hum Issue SOLVED

Postby Golear » Mon Sep 24, 2018 9:24 pm

The cork + plastic coaster picks up electrical/magnetic energy from the motor block.... and acts as an antenna?
And then this is picked up by the cartridge?

Is it the cork or is it the plastic? Or is it the cork AND plastic?

What's the voltage of the motor block with respect to Earth? Set a multimeter to read AC voltage, turn the motor on, then touch one probe on the motor block and one probe to Earth. (Don't do this if you're not confident about sticking the probe into the Earth in a power strip. Needless to say, don't put the probe into the live or neutral.)
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Re: Weird Hum Issue SOLVED

Postby 930turbo » Mon Sep 24, 2018 9:27 pm

Hi Brf ,WntrMute
Is the ground wire at the bearing well of the classic aluminium platter in the TNT 6 really necessary . My HR-X w/c essentially has the same platter does not need one . No hum nor static issues in the HR-X . There is even no provision for a ground wire .

930
VPI TNT 6,w/Kuzma Stogi Ref 313 VTA,Benz Micro Gullwing SLR,VPI HR-X 12.7 Lyra Kleos,ARC REF5SE line stage, REF PHONO 2SE,SP10Mk2preamp,ARC REF610T monoblocks,a pair of D79B amps,EC21active electronic X over, Duntech C5000 Princess spkr,Magnepan MG3A spkr
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Re: Weird Hum Issue SOLVED

Postby Brf » Tue Sep 25, 2018 7:39 am

930turbo wrote:Hi Brf ,WntrMute
Is the ground wire at the bearing well of the classic aluminium platter in the TNT 6 really necessary . My HR-X w/c essentially has the same platter does not need one . No hum nor static issues in the HR-X . There is even no provision for a ground wire .

930


I always ground my table's bearing. Every TT environment is different.
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Re: Weird Hum Issue SOLVED

Postby WntrMute » Tue Sep 25, 2018 8:10 am

The coasters are a thin layer of cork bonded to a thin layer of plastic.
I've found, in both my systems, that grounding the bearing helps prevent static. Never had a hum issue before this weird situation.
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