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turntable " thump " sound when not running

Hi I have a question that’s been in the back of my to do list for the longest time so I decided to join the forum after reading so many postings over the years from this legendary community. :) I have a thump sound the same way it sounds when dropping the stylus on a record. it occurs about every 10-20 seconds or so regardless if the turntable platter is spinning or off. I am guessing its electrical? what causes this? I have a pretty decent setup yet modest compared to most of you guys in here and I think I shouldn’t have to deal with this thumping sound.  By the way this sounds only occurs on the phono.  the cd, tape, etc doesnt have this problem. 

Adcom GFP-750 preamp
Adcom GFA-555II amp
Jolida JD9 II
Music Hall 5.1SE TT (Sumiko Blue Point no. II)
LSA-1 Statement speakers

I have the turntable power supply adapter plugged into the back of the preamp power ports.
Should I move it to a different outlet? Maybe I just answered my own question.

128x128obeerbongkenobi
wlutke
725 posts
 
Try disconnecting your turntable from the phono pre and short the individual phono inputs (not to each other). If it still thumps, it’s likely the phono pre has a bad tube or is going bad.

czarivey
5,946 posts
 
When I don't play my records, my preamp is on MUTE.
When I lay down my needle on record surface, my preamp is on MUTE
When the needle starts surfing the record i UNMUTE my preamp.
When I want to pull up needle from my record, my preamp is on MUTE.

If you don't have MUTE switch, use input selector to switch to AUX or any other line input.

obeerbongkenobi's avatar
obeerbongkenobi OP
3 posts
 
Thanks for all your feedback everyone.  I ended up unplugging the Turntable power supply from the back of the preamp and plugged it directly into the wall outlet and then turned on everything so i could listen for the sound and it was still there.  So then I started to jiggle the ground wire that runs from the turntable base to the Jolida Phono preamp and the hum would come and go.  then i noticed the end from the jolida pulled out completely and sound went away.  neither ground hum or the thump sounds!!.  I detached it from the TT as well and just took out the ground wire altogether.  Strange. 
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