Author Topic: clip on RF chokes  (Read 6102 times)

Offline papabearjew

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clip on RF chokes
« 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

Offline MacGeek

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Re: clip on RF chokes
« Reply #1 on: October 25, 2014, 05:13:23 PM »
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.
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Offline papabearjew

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Re: clip on RF chokes
« Reply #2 on: October 25, 2014, 05:40:31 PM »
@MacGeek. Everything you said to try has been done to no avail. The cycles of the hum does vary with the rpm setting

Offline ataudio

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Re: clip on RF chokes
« Reply #3 on: October 25, 2014, 07:36:06 PM »
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.

Offline Sir Thrift-a-Lot

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Re: clip on RF chokes
« Reply #4 on: October 25, 2014, 10:43:47 PM »
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

Offline papabearjew

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Re: clip on RF chokes
« Reply #5 on: October 25, 2014, 11:11:36 PM »
Nope...Not Grado Hum. Same thing happens with the OEM ReVox/AKG, Stanton, Shure and AT cartridges

Offline Sir Thrift-a-Lot

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Re: clip on RF chokes
« Reply #6 on: October 26, 2014, 01:01:33 AM »
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.

Offline MacGeek

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Re: clip on RF chokes
« Reply #7 on: October 26, 2014, 07:03:54 AM »
Which table? Belt or direct drive?
Mac stuff, Sony HDR-F1HD AM/FM/HD tuner, Denon DRS 810 cassette, Denon CDR-W1500 CD recorder, Music Hall MMF-9 w/B&O MMC2, B & O 4002 w/B & O 20 CL, Revox A-77

Offline papabearjew

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Re: clip on RF chokes
« Reply #8 on: October 26, 2014, 12:12:09 PM »
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

Offline ataudio

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Re: clip on RF chokes
« Reply #9 on: October 26, 2014, 05:06:53 PM »
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.

Offline papabearjew

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Re: clip on RF chokes
« Reply #10 on: October 26, 2014, 07:28:11 PM »
All caps have already been replaced

Offline ataudio

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Re: clip on RF chokes
« Reply #11 on: October 26, 2014, 10:48:57 PM »
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?

Offline papabearjew

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Re: clip on RF chokes
« Reply #12 on: October 26, 2014, 10:58:05 PM »
Everything has been done but item 4. This started several months ago.

Offline ataudio

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Re: clip on RF chokes
« Reply #13 on: October 26, 2014, 11:26:03 PM »
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

Offline MacGeek

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Re: clip on RF chokes
« Reply #14 on: October 27, 2014, 06:38:07 AM »
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).
Mac stuff, Sony HDR-F1HD AM/FM/HD tuner, Denon DRS 810 cassette, Denon CDR-W1500 CD recorder, Music Hall MMF-9 w/B&O MMC2, B & O 4002 w/B & O 20 CL, Revox A-77