Vintage HiFi Audio Forum
Repair / Help Forum => Repair / Help => Topic started by: papabearjew on October 25, 2014, 02:08:05 PM
-
I'm still getting cyclic hum (probably from motor) on my turntable. Any chance that clip on RF chokes on the audio cables would help?
Thx
-
PBJ-I doubt it. Is it the same at all speeds? Do you have a ground wire from the 'table to the pre-amp? If not try adding one, or if so, disconnect it. Sometimes reversing the A/C plug helps.
-
@MacGeek. Everything you said to try has been done to no avail. The cycles of the hum does vary with the rpm setting
-
If its 60/120 hz hum they won't help at all. Their impedance doesn't rise until well into the RF range.
Can you borrow an isolation transformer? Isolate the TT from all other components.
-
Changes with the speed? Sorry to tell you, you have the famous "Grado hum". Paint some copper shielding on your platter or (much quicker and easier) just get yourself an AT or Shure cartridge. The hum will go away.
http://www.audiokarma.org/forums/showthread.php?t=46091 (http://www.audiokarma.org/forums/showthread.php?t=46091)
-
Nope...Not Grado Hum. Same thing happens with the OEM ReVox/AKG, Stanton, Shure and AT cartridges
-
Oh. Can you hear anything when the amp is off, like any sign of rubbing or grinding at the motor? The fact that it changes with RPM really makes me think it is somehow motor based.
-
Which table? Belt or direct drive?
-
Definitely seems motor based. Hum is through speakers and is most annoying with classical music during quiet passages. T/T is ReVox B795 which is direct drive
-
Given its DD and older you might wanna start looking at swollen/leaky caps. According
to an article I read on the web the motor has a tach that is compared to a ref frequency.
Aging caps in the power supply, drive circuit, etc could be your culprit. Treat it like a vintage amp...start with the caps.
-
All caps have already been replaced
-
Many years ago when I had a TT I must have been lucky. Never had any issues with hum on my old AR, B&O, a couple of Duals and finally my Micro Seiki. Throw in in some super cheap Technics, Fisher, etc. Never any issues. Without knowing what you've tried I would
1) move TT to a second system to see if problem follows TT....maybe its your preamp's phono section that has the issue
2) relocate TT away from large transformers
3) move cables away from large transformers
4) try isolation transformer on TT ac line
5) check cart wires from cart to rca jacks
6) try cheater plugs on certain equipment to reverse plug polarity
Did this just start?
-
Everything has been done but item 4. This started several months ago.
-
Hmmm.....any major changes around the start time? New this or that or corresponds with this hum starting?
Maybe even a new appliance that could somehow affect the TT????? Super long shot.
This seems like a very complex TT. Not sure how long I could live with this. I had a
Jolida tube amp that hummed. Sent it back twice. I imagine this would drive me nuts
If you can't borrow an ISO transformer you could make a cheap temp setup with two identical transformers back to back.
I've done this with a pair of 120/220v travel transformers.
Good luck
-
PBJ, do any of the components in the system have a three wire plug? If so, try lifting the grounds (at least as a test).
-
PBJ, do any of the components in the system have a three wire plug? If so, try lifting the grounds (at least as a test).
@MacGeek, I'll double check. I remember when I was getting terrible hum through my headphone amp I used a 3 prong to 2 prong adapter on the headphone amp power plug and it solved the problem.
-
An isolation transformer is probably better, but lifting the third prong may help t identify the problem
-
Where do I get an isolation transformer?
-
I don't have a clue. I cheat and just lift the grounds. I expect someone on this Forum knows.