Turntable HUM

[SimplerTimes]

I have a Garrard DDQ-550 direct drive turntable that I picked up for cheap. As far as early ‘80’s turntables go, it seems to be a decent unit and I want to keep it as a spare. So I connected it to my Sansui G-6000 to test and it worked fine for a few moments, but as I was manually moving the tone arm and checking the auto return and speed selector, it developed a very loud hum through the right channel. I rechecked the ground wire connection to the receiver and could see no problem. The hum seemed to get better as I touched the tone arm and gimbal(?) mount area so I decided to check for an internal grounding issue. After removing the bottom cover and checking the RCA cables and ground wire for continuity to their respective solder points, all checked out ok. I also connected the Garrard to another receiver with a known good phono section as the Sansui is new to me and I wanted to eliminate it as the problem and it still hummed. It appears to me to be either a problem between where the input cables are soldered to the tone arm assembly or possibly something on the circuit board. Does anyone have an idea as to what I should check next? I have looked online for a schematic and have found nothing. Any advice would be appreciated.
Thanks,
Brian

 

[Tim D]

Ah, turntable hum. So many ways it can happen.

- Removable headshell contacts are intermittent on the headshell or the tonearm. Clean them.
- RCA cables are going bad. Replace them.
- Connectors at the cart are loose or corroded. Correct or clean as necessary.
- Broken tonearm wire. Replace as needed.

Sometimes you need to use a low power ohm meter to trace it down. I usually start across each cable to see if it is the same resistance on both cable ends. Usually you'll find a high resistance connection due to one of the items above.

Good luck.

 

[SimplerTimes]

I think I figured it out. @ Tim D, Before I read your reply I cleared my mind and took a closer look at my problem. Here is what I did. First, I reflowed the solder connection to the ground wire, no change, then I looked closely at both the cart and head shell wire connections and cleaned the contacts with deoxit. Also no change. Next, I replaced the grounding wire and crimped a lug on the end. Still hummed. Just as I was ready to give up for the night, I tried reversing the RCA cables to the receiver. This time the hum went away. I then cleaned these and reconnected but the right channel hum returned. As I was touching the tonearm in different places to see if conditions changed, I noticed that the head shell position into the tonearm was very sensitive with regard to the amount of hum. Bottom line is I think it is a combination of all of these issues. I found that if I slightly pulled the head shell away from the tonearm before tightening the lock screw knob, the hum disappeared. So far the turntable has been playing with no more issues.