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Grounding a turntable with no ground connection

Mark Casazza

Mark Casazza

New Member
I have a Teac TN-300 turntable attached to a Rogue Audio Cronus Magnum II. (A better turntable is planned for the Fall). I have a distinctive 60Hz hum. If I change out the cables things can get a bit better or worse. I am currently using a 6' double shielded cable. It provides the least hum. This turntable has no ground connector, so I opened things up, found the electric ground plane and tried to ground it to the amp. Things get much worse when grounded. Reversing the way the turntable's power is plugged in makes no difference. I have a similar situation in my garage with a JVC AL-F3 turntable and Teac AG-V3020 receiver.
upload_2023-4-4_21-40-25.png

Clearly using the electric ground is incorrect in this case. The TN-300 has a built in pre-amp which I do not use as well as a USB feature. I'm considering removing the board and connecting the tonearm wires directly to the RCA jacks. The turntable is running an AT-VM95SH stylus. It has 4 wires which I assume are 2 per channel. It should be pretty trivial to track wire colors to ground or signal for each channel. Then, with the tonearm and stylus isolated from the power to the motor, try a ground connection again.

I'm looking for suggestions from anyone with experience adding a ground to a turntable that does not come with one or a similar situation. I find it odd that both in my office and the garage that adding the ground increased the hum. Fortunately, I found a failing cable in the garage so now that hum is minimal considering the equipment. I know my way around electronics enough to find this baffling. Clearly there is a gap in my knowledge especially in the 60 cycle hum department.

I also have an APC Line-R 1200 that I can bring to the party. I use it when I work from my camper and have computers plugged into state park electric.
 
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Mark Casazza said:
I have a Teac TN-300 turntable attached to a Rogue Audio Cronus Magnum II. (A better turntable is planned for the Fall). I have a distinctive 60Hz hum. If I change out the cables things can get a bit better or worse. I am currently using a 6' double shielded cable. It provides the least hum. This turntable has no ground connector, so I opened things up, found the electric ground plane and tried to ground it to the amp. Things get much worse when grounded. Reversing the way the turntable's power is plugged in makes no difference. I have a similar situation in my garage with a JVC AL-F3 turntable and Teac AG-V3020 receiver.
View attachment 2849610

Clearly using the electric ground is incorrect in this case. The TN-300 has a built in pre-amp which I do not use as well as a USB feature. I'm considering removing the board and connecting the tonearm wires directly to the RCA jacks. The turntable is running an AT-VM95SH stylus. It has 4 wires which I assume are 2 per channel. It should be pretty trivial to track wire colors to ground or signal for each channel. Then, with the tonearm and stylus isolated from the power to the motor, try a ground connection again.

I'm looking for suggestions from anyone with experience adding a ground to a turntable that does not come with one or a similar situation. I find it odd that both in my office and the garage that adding the ground increased the hum. Fortunately, I found a failing cable in the garage so now that hum is minimal considering the equipment. I know my way around electronics enough to find this baffling. Clearly there is a gap in my knowledge especially in the 60 cycle hum department.

I also have an APC Line-R 1200 that I can bring to the party. I use it when I work from my camper and have computers plugged into state park electric.
Click to expand...


How close is your amp to the table? It's not uncommon to pick up noise from the tranny if too close.

Try and keep your interconnects from running parallel to high voltage cords.

Is your cartridge / headshell if removable seated properly?
 
This could be a house wiring issue. Such as a neutral tied to ground on wall connector(s). First check the house fuse/circuit breaker box and next the wall connectors.
 
On this table it seems to be a easy one to test the grounding to other equipment. Even without a separate ground wire the RCA's will act as it.

Remove the headshell and using a Ohm Meter on RX1 touch the four pins inside the arm collar. Two will be the positive RT/LF and two the negatives. The negatives will if everything is OK inside of the table, it will be common with the chassis of other equipment connected.
 
Wow, quite a few suggestions. Let me try to answer each question:
  1. How close is your amp to the table? It's not uncommon to pick up noise from the tranny if too close.
    1. They are side by side, but the cable drops to the floor immediately and avoids the power transformer (by accident). I did move things around a bit and I see that as the cable approaches the power transformer the hum increases. Moving the table a few feet away does not help and as the cable comes up because it has less slack it actually approached the transformer making things worse.
    2. I will have to remember this one. It is so obvious, but I never thought of it.
  2. Try and keep your interconnects from running parallel to high voltage cords.
    1. This is the case. My amp's power cord is actually shielded too. Rogue made a point to document this because people were replacing them because they were "ugly". Crazy folks.
  3. Is your cartridge / headshell if removable seated properly?
    1. Yes, this was checked and all looks solid. The 4 wires off the stylus are deeply seated into the head and the head is firmly attached. As a test I removed the head and the hum went down from -40db to -45db.
  4. The other thing you can do is slightly unwind one of the case screws & wind a bared cable around it & screw back up.
    1. I'm not sure I'm following this suggestion. When I pulled the unit apart I confirmed that the metal panel that the RCA jacks were on was in fact the electrical ground. I did loosen one screw and attached a wire. That is how I tested connecting it to the ground connection on the amp.
  5. This could be a house wiring issue. Such as a neutral tied to ground on wall connector(s).
    1. Wish it was, that would be so easy, but I installed these lines a few years back. They are correct and properly grounded.
Interesting experiment. I pulled the RCA cables out of the back of the turntable. The hum was greatly reduced, but as the cords approached the connection point the hum returned, even without contact. A good 2" air gap!. I fiddled around with how the cord was lying to see it that was causing the hum. Nothing obvious. Then I unplugged the turntable's wall wart. The hum went away. Found it? No! Plug the RCA plugs in and even with the turntable unplugged (from AC) the hum returns.

The turntable uses a humble 12V wall wart. I pulled out a high quality 12V power supply that I use for my astro-photography telescope and computer. It has a verified flat 12V output with no wobble. Problem is the same using that power supply. The hum is no better with it is plugged in and if the disconnected RCA wires approach that wire a hum grows strong.
 
Mark Casazza said:
Wow, quite a few suggestions. Let me try to answer each question:
  1. How close is your amp to the table? It's not uncommon to pick up noise from the tranny if too close.
    1. They are side by side, but the cable drops to the floor immediately and avoids the power transformer (by accident). I did move things around a bit and I see that as the cable approaches the power transformer the hum increases. Moving the table a few feet away does not help and as the cable comes up because it has less slack it actually approached the transformer making things worse.
    2. I will have to remember this one. It is so obvious, but I never thought of it.
  2. Try and keep your interconnects from running parallel to high voltage cords.
    1. This is the case. My amp's power cord is actually shielded too. Rogue made a point to document this because people were replacing them because they were "ugly". Crazy folks.
  3. Is your cartridge / headshell if removable seated properly?
    1. Yes, this was checked and all looks solid. The 4 wires off the stylus are deeply seated into the head and the head is firmly attached. As a test I removed the head and the hum went down from -40db to -45db.
  4. The other thing you can do is slightly unwind one of the case screws & wind a bared cable around it & screw back up.
    1. I'm not sure I'm following this suggestion. When I pulled the unit apart I confirmed that the metal panel that the RCA jacks were on was in fact the electrical ground. I did loosen one screw and attached a wire. That is how I tested connecting it to the ground connection on the amp.
  5. This could be a house wiring issue. Such as a neutral tied to ground on wall connector(s).
    1. Wish it was, that would be so easy, but I installed these lines a few years back. They are correct and properly grounded.
Interesting experiment. I pulled the RCA cables out of the back of the turntable. The hum was greatly reduced, but as the cords approached the connection point the hum returned, even without contact. A good 2" air gap!. I fiddled around with how the cord was lying to see it that was causing the hum. Nothing obvious. Then I unplugged the turntable's wall wart. The hum went away. Found it? No! Plug the RCA plugs in and even with the turntable unplugged (from AC) the hum returns.

The turntable uses a humble 12V wall wart. I pulled out a high quality 12V power supply that I use for my astro-photography telescope and computer. It has a verified flat 12V output with no wobble. Problem is the same using that power supply. The hum is no better with it is plugged in and if the disconnected RCA wires approach that wire a hum grows strong.
Click to expand...

I'm betting one of the ground connections on one of the RCA jacks is loose, does the issue get better/worse if you wiggle the interconnects one at a time?

I had this issue recently with my Well Tempered Lab Turntable. The ground for each channel is connected to an O terminal dependent on the tightness of the nut holding the jack. If the cable end is turned during installation/removal it's possible to loosen the nut, this is what I'm thinking happened.

My cables are especially designed as compression connectors, loosen the connector, slide on, tighten the connector and they grab.

After I tightened the nuts on the jacks with needle nose pliers all was good again. Care had to be taken the O terminals didn't turn with the nut so as not to break the tiny phono ground wires attached.
 
Wiggling the cables caused no issues. I will take things apart and check the internals. The amp makes this pretty easy as does the turntable.

Assuming I find no issue, while I have the turntable apart what harm is there to direct connect the tone arm wires to the RCA jacks? Any special solder to use?

I won't be getting to this until next week as I have a wedding to attend to a few states away.
 
You might be onto the solution, you have to eliminate the ground connection through the RCA wiring completely, and just use the external wire (as most turntables have, but not yours). Some phono preamps go crazy with ground run through the common wire on RCA cable.
 
Ah! Great tip. So the RCA jacks need to be mounted to an insulated panel, not with a common "ground". Then use a separate ground wire to extend the amp's ground plane to the turntable, but the signal lines are totally isolated. Sounds like the turntable will be taken apart Monday evening.
 
Mark Casazza said:
Ah! Great tip. So the RCA jacks need to be mounted to an insulated panel, not with a common "ground". Then use a separate ground wire to extend the amp's ground plane to the turntable, but the signal lines are totally isolated. Sounds like the turntable will be taken apart Monday evening.
Click to expand...
Ideally the tonearm should be grounded, but not through the signal cable. Unfortunately many vintage cartridges have metal tabs grounding the signal ground to headshell. I hope it works in your case.
 
UPDATE: I opened up the turntable and found that somewhere inside the tonearm the left and right negative lines are shorted. I confirmed this with a multi-meter and the stylus removed as well as the tonearm wires disconnected from the Teac circuit board. I proceeded anyway and connected the tonearm wires to 2 new gold plated RCA jacks. The tonearm had a ground cable so I connected that externally as well. It is very much an experimental setup not safe for long term use, but it can prove or disprove the concept.

RESULTS:
  1. 60Hz hum remains at pretty much the old level.
  2. I did notice a lot of other noise is reduced if the turntable is unplugged so the pre-amp /USB is noisy even to induce noise around it.
  3. The one BIG difference is now connecting the ground wire to the amp removes much of the non-60Hz noise.
I could remove the pre-amp circuit board entirely to remove the non-60Hz noise, but that will require powering the motor another way. I have a high quality variable power supply to start with, but this seems like a lot of work knowing the 60Hz hum is the real problem.

Tomorrow I'm going to try a 1' RCA cable to see if that helps at all, but I'm still looking for ideas. Is it time to upgrade to the AUDIO-TECHNICA AT-LP120XUSB? That will take the stylus from the Teac.
 
Mark Casazza said:
UPDATE: I opened up the turntable and found that somewhere inside the tonearm the left and right negative lines are shorted. I confirmed this with a multi-meter and the stylus removed as well as the tonearm wires disconnected from the Teac circuit board. I proceeded anyway and connected the tonearm wires to 2 new gold plated RCA jacks. The tonearm had a ground cable so I connected that externally as well. It is very much an experimental setup not safe for long term use, but it can prove or disprove the concept.

RESULTS:
  1. 60Hz hum remains at pretty much the old level.
Click to expand...
And if you unplug the power cord from the wall --- the 60Hz goes away? There maybe be a loose connection or solder point inside the turntable, where the power cord connects to a board.
 
Mark Casazza said:
UPDATE: I opened up the turntable and found that somewhere inside the tonearm the left and right negative lines are shorted. I confirmed this with a multi-meter and the stylus removed as well as the tonearm wires disconnected from the Teac circuit board. I proceeded anyway and connected the tonearm wires to 2 new gold plated RCA jacks. The tonearm had a ground cable so I connected that externally as well. It is very much an experimental setup not safe for long term use, but it can prove or disprove the concept.

RESULTS:
  1. 60Hz hum remains at pretty much the old level.
  2. I did notice a lot of other noise is reduced if the turntable is unplugged so the pre-amp /USB is noisy even to induce noise around it.
  3. The one BIG difference is now connecting the ground wire to the amp removes much of the non-60Hz noise.
I could remove the pre-amp circuit board entirely to remove the non-60Hz noise, but that will require powering the motor another way. I have a high quality variable power supply to start with, but this seems like a lot of work knowing the 60Hz hum is the real problem.

Tomorrow I'm going to try a 1' RCA cable to see if that helps at all, but I'm still looking for ideas. Is it time to upgrade to the AUDIO-TECHNICA AT-LP120XUSB? That will take the stylus from the Teac.
Click to expand...
Are negative lines also shorted with the tonearm body inside the tonearm? If yes, there is not much you can do other than rewiring the tonearm.
 
Are negative lines also shorted with the tonearm body inside the tonearm? If yes, there is not much you can do other than rewiring the tonearm.
Click to expand...

If that is as big a deal as you describe I will give it a try. Not sure how easy it will be to get into it without damaging it, but I'll give it a go this weekend.
 
Mark Casazza said:
If that is as big a deal as you describe I will give it a try. Not sure how easy it will be to get into it without damaging it, but I'll give it a go this weekend.
Click to expand...
Don't have to do it if neutrals and ground are not joined inside the tonearm, although left and right neutral joined together is not ideal either.
 
Left & right neutral are joined. They are isolated from the ground. Not a total disaster. There is not much to the tone arm, it will either come apart easy or not.
 
Have you tried different RCA interconnects? Have a couple of set of interconnects that can’t be used in certain locations, assuming it’s their shielding type, or lack thereof….anyway they will induce hum when others do not.


VR
Andy
 
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