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Moving coil cartridge (AT OC-9) and Hum

I have 2 systems, the first uses an SME/Thorens with Supex MC cartridge into a Accuphase C-200 pre-amp. The second uses an OriginLive modified RB250/Revolver turntable with an AT OC-9 MC cartridge into a Carver CT3 preamp. Both systems use electronic cross-overs to feed multi-amp speaker systems. I have a Marshal Leach designed battery powered pre-preamp that when used on the first system produced no audible hum. Moving this pre-preamp to the second system however produced hum. The second pre-preamp is an older Dayton-Wright version that seems meticulously made and has a outboard remote power supply. It however produces hum on both systems albeit quite a bit less on the first system than on the second. The battery powered unit has much less hum on the second system than the Dayton Wright but the level is still unaccepatable. The hum is only audible while switched to phono on both systems. Is the OC-9 cartridge the culprit or is it the Carver CT-3 that makes the second system so prone to hum? I suppose I should switch turnatbles. The second system was only recently upgraded and with a MM cartridge, the hum was nonexistant, so I am very suspicious of the OC-9. Has anyone had experience with hum on MC cartridges (in particular the Audi-Technica OC-9) and can offer remedies?
rfj
9 responses Add your response
detlof
1,899 posts
 
Hum is practically normal with MC cartridges, if you don't try to ground the TT, TA, preamp combination. It takes some experimenting. In your otherwise very thorough description, you did not mention your grounding scheme, so I thought I'd give my 2cents worth.
rfj OP
43 posts
 
Thanks for the input, I have grounded everything, but the hum continues.
detlof
1,899 posts
 
RFJ, its a shame you did not get expert response. Perhaps the Agoners are as tired of hum as you must be. Have you licked the problem? If not, having EVERYTHING grounded, as you said, have you tried taking some of the grounds away?
Regards,
sedond
1,387 posts
 
is the revolver similar in layout, w/a similar motor as a regsa 'table? the regas are known to induce hum in non-shielded cartridges...

doug

rfj OP
43 posts
 
The revolver, I believe does have a similiar AC synchronous motor but the belt drives the perimeter of the platter rather than a sub platter. So would a DC servo motor be less usceptible to hum with MC? Is there any experience with this? It's an intriguing concept and I believe I can test by unplugging turntable while switched to phono. If hum goes away, than we will know AC synchronous is the culprit. We will try out tonight. Stay tuned for feed back. Thank you Doug for input!
rfj OP
43 posts
 
I tried turning the motor off while the pre-amp was set to phono. The hum did not go away nor did it even change. The hum appears to becoming from the cartridge. The saga continues.
sedond
1,387 posts
 
i'd try switching the 'tables, if ya haven't done it yet. mite also try a s/s pre-preamp - aren't yours tubed? while i like toobs, they can be noisy on fono-stages w/low-output cartridges...

doug s.

musicdoc
320 posts
 
What about the connection and dressing of the headshell leads? Another thought is degaussing the cartridge. Just "thinking out loud." Good Luck.
rfj OP
43 posts
 
I have solved the "hum" problem and I do feel stupid. But hopefully others will not have to repeat my angst. I did switch out turntables and it was when switching back that the source of the hum became evident. The "Revolver" has a 3 prong AC plug and when you plug it in the "hum" starts and if you unplug it the "hum" stops. Use a cheater plug (2 prong) with it and the hum stops. Case closed. What a dope! Watch out for those 3 prong plugs!
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