Thanks agdr. My cartridge (AT440MLa) is a moving magnet, not moving coil, and in any case I don't feel comfortable monkeying with that. And I have no fluorescent lights in the room or anywhere near the hifi gear. But your wiring ideas sound reasonable. I've partially replaced the wiring on my Thorens TD-165 with shielded cable (single inner conductor though). I'll be interested to hear how it sounds when I finish it.
I'm particularly interested in the two-conductor coax style wiring and will research that more. The links you provided will be quite helpful. I'll post back with any reports.
I do expect to get some hum even after addressing most of the problems, but I can live with a little hum. It's the big hum I'm getting now that drives me crazy.
OT - Canned about a gallon of syrup today, more to come! PM me and I can send you a small sample. It's a little smokey b/c I don't have a fancy rig, just a very DIY boiler.
I'm particularly interested in the two-conductor coax style wiring and will research that more. The links you provided will be quite helpful. I'll post back with any reports.
I do expect to get some hum even after addressing most of the problems, but I can live with a little hum. It's the big hum I'm getting now that drives me crazy.
OT - Canned about a gallon of syrup today, more to come! PM me and I can send you a small sample. It's a little smokey b/c I don't have a fancy rig, just a very DIY boiler.
One of the keys is not connecting the other end of the shields so there are no ground loops. Note in that single conductor diagram the shields turn back into the signal ground, so they stay isolated at the other end. Then the rest of the shields are single-point grounded. But then there is always what happens through the third-wire power plug! 
Grounding gets tricky.
If all goes well you should be able to short the connections for one channel together right at the back of the cartridge and get no hum, same as shorting the amp inputs at the RCA connector. If that works, but you still get hum with the contacts unshorted, then like AndrewT says your cartridge itself is picking up some hum.
I might take you up on that syrup sample! Thanks for the offer.
Grounding gets tricky.If all goes well you should be able to short the connections for one channel together right at the back of the cartridge and get no hum, same as shorting the amp inputs at the RCA connector. If that works, but you still get hum with the contacts unshorted, then like AndrewT says your cartridge itself is picking up some hum.
I might take you up on that syrup sample! Thanks for the offer.
Thanks, agdr. I know about connecting one end of shielding to avoid ground loops and will be sure to do that when the time comes. I've read connecting at the source end is preferrable (not sure why) but would that be true for a TT? Grounding is a PAIN, yet SO very important. Conceptualizing the loops and then finding them hurts my head. 
Is there some kind of shielding technique for cartridges you can point me to? I'll look into it myself, but suggestions are certainly welcome. I'll also try shorting the pins on the cartridge. I assume you mean shorting each channel, + to -. If I still get hum, the wiring is picking up the hum (or there's a ground loop), while if not, as you say, it's the cartridge coils.
On another related thread about extra hum I was getting from the turntable just before I built the PS (http://www.diyaudio.com/forums/analogue-source/231123-phono-hum-turntable.html) someone asked about whether the tonearm tube were grounded (it is) as that would provide some shielding for the tonearm wiring. I'm thinking at this point there's some kind of ground loop associated with the TT wiring, so will look into that carefully.
I guess in a way it's good to find out the issue is not the amp or PS, but rather the TT/Cart/leads. But I can't imagine if I were boosting by 60dB for an MC cartridge...
PM me your address if you want to try some syrup.
Is there some kind of shielding technique for cartridges you can point me to? I'll look into it myself, but suggestions are certainly welcome. I'll also try shorting the pins on the cartridge. I assume you mean shorting each channel, + to -. If I still get hum, the wiring is picking up the hum (or there's a ground loop), while if not, as you say, it's the cartridge coils.
On another related thread about extra hum I was getting from the turntable just before I built the PS (http://www.diyaudio.com/forums/analogue-source/231123-phono-hum-turntable.html) someone asked about whether the tonearm tube were grounded (it is) as that would provide some shielding for the tonearm wiring. I'm thinking at this point there's some kind of ground loop associated with the TT wiring, so will look into that carefully.
I guess in a way it's good to find out the issue is not the amp or PS, but rather the TT/Cart/leads. But I can't imagine if I were boosting by 60dB for an MC cartridge...
PM me your address if you want to try some syrup.
Here's the latest report. I've now hooked up a second TT that has no ground wire (and whose tonearm is NOT connected to the negative of the RCAs, so is not grounded at all). It's a Dual 1219. This turntable has less noise, though it does have a buzz (sounds like typical ground loop frequency, but more scratchy). This noise is quieter but more annoying. Arggghhh.
On my Luxman, I shorted the blue and white (left channel) pins with tonearm wires attached as agdr suggested and got seriously increased hum. Quite loud.
At this point, I'm likely to try some of the grounding schemes from agdr's links as well as AndrewT's suggestion once I finish wiring up my Thorens. But first I will check to see that all the metal is actually grounded on the Luxman. Yesterday I read up on the Luxman and found that some consider it quite noisy, in particular with hum. If not for the hum, the Luxman sounds quite nice, so I feel like it's worth working on.
Well, despite my frustrations with this, I greatly appreciate all the help, and I haven't given up yet!
On my Luxman, I shorted the blue and white (left channel) pins with tonearm wires attached as agdr suggested and got seriously increased hum. Quite loud.
At this point, I'm likely to try some of the grounding schemes from agdr's links as well as AndrewT's suggestion once I finish wiring up my Thorens. But first I will check to see that all the metal is actually grounded on the Luxman. Yesterday I read up on the Luxman and found that some consider it quite noisy, in particular with hum. If not for the hum, the Luxman sounds quite nice, so I feel like it's worth working on.
Well, despite my frustrations with this, I greatly appreciate all the help, and I haven't given up yet!
If you don't get it resolved, post a sketch of exactly how your wiring is set up, similar to how it is done in those links. Show which sections are coax, which are unshielded wire, and most importantly exactly what points along the way are grounded to what. Be sure to include any 3rd wire power plug grounds and where they connect. Also show tonearm ground, and if the turntable itself is floating on springs how that is grounded. Photos would be good too - someone here might have an "aha" moment on seeing a photo.
Just as a thought experiment, since you could short the amp RCAs and get no hum, you should be able to plug a length of coax cable into those, short the end, and still get no hum. So something has to be happening along the way going from the amp RCAs to the cartridge.
Just as a thought experiment, since you could short the amp RCAs and get no hum, you should be able to plug a length of coax cable into those, short the end, and still get no hum. So something has to be happening along the way going from the amp RCAs to the cartridge.
Thanks, agdr. I'll try to sketch out the wiring and setup soon, along with a photo. I'll also try the coax cable connection to see if it's picking up in the wiring. Not entirely sure, though, what wiring the TTs use (are they always coax?).
Finally, I've posted some audio clips of the two noises I'm getting. The hum from a Luxman PD-277 and the buzz from a Dual 1219. Recording directly from the jfet amp resulted in signal level that's too low (I can only hear through headphones on my computer output), so I "normalized" them in Audacity. Result is the other noise floor (hiss, etc.) from the amp is much higher than it sounds on the system. Try to ignore that. The clips are here (with notes about what's going on below the link):
Luxman Hum Normalized
0-5 sec - TT connected, not on. (there is a low hum)
5-11 sec - TT power switch on, platter not turning
11-20 sec - tonearm moved over platter, platter spinning
Dual Buzz Normalized
0-4 sec - amp hiss with no TT motor running and cables shut down (Dual 1219 switches off the interconnects until the arm is down)
11-18 sec - moving the arm across the face of the platter (same noise whether moving by hand or by wooden stick)
18-25 sec - tonearm stationary over the platter, not touched
I realize there may be two different problems going on with these 2 turntables.
Thanks again,
Carl
Finally, I've posted some audio clips of the two noises I'm getting. The hum from a Luxman PD-277 and the buzz from a Dual 1219. Recording directly from the jfet amp resulted in signal level that's too low (I can only hear through headphones on my computer output), so I "normalized" them in Audacity. Result is the other noise floor (hiss, etc.) from the amp is much higher than it sounds on the system. Try to ignore that. The clips are here (with notes about what's going on below the link):
Luxman Hum Normalized
0-5 sec - TT connected, not on. (there is a low hum)
5-11 sec - TT power switch on, platter not turning
11-20 sec - tonearm moved over platter, platter spinning
Dual Buzz Normalized
0-4 sec - amp hiss with no TT motor running and cables shut down (Dual 1219 switches off the interconnects until the arm is down)
11-18 sec - moving the arm across the face of the platter (same noise whether moving by hand or by wooden stick)
18-25 sec - tonearm stationary over the platter, not touched
I realize there may be two different problems going on with these 2 turntables.
Thanks again,
Carl
Just as a thought experiment, since you could short the amp RCAs and get no hum, you should be able to plug a length of coax cable into those, short the end, and still get no hum. So something has to be happening along the way going from the amp RCAs to the cartridge.
All is very quiet if I do this. No hum from just the cables, so I'm increasingly convinced it's the cartridge. Note the hum gets louder as the cart/arm move toward the spindle. Motor is underneath the platter in the center (it's direct drive). Arm is grounded so should shield the arm wiring fairly well.
After doing some other reading, I found that the neon strobe for the platter may cause hum in some cases. Also read where there was a bad batch of AT440MLa cartridges that were susceptible to hum due to bad shielding. I'll try pulling that and installing another cart. The TT came with an MA 2002 cart (ceramic/piezo) and it sounds like they are very resistant to hum, which may be why it was installed.
That really does seem like a cartridge problem. AndrewT nailed it.
I agree, swapping out the cartridge would be a good test, especially with the ceramic type.The hum is apparently radiated from the AC in the TT, and picked up by the signal wiring. There is apparently enclosed geometic area in loops formed by the conductor pairs, in the AC or signal wire pairs, or both, which makes them into good antennas (transmitting and receiving). (See Faraday's Law.)
If shorting a signal wire pair just before it attaches to the cartridge does not stop the hum, or makes it worse, the problem could be that the wires are acting as a loop antenna. Shorting them would just mean that the loop is complete and current could be induced in it, by the AC fields. If they are acting as an antenna, then disconnecting them from the cartridge but NOT shorting them should greatly reduce the hum.
If it hums with the TT turned off, does the hum then stop (or reduce significantly) if you unplug the TT's AC Mains from the wall?
If so, then proceed with mitigations, per below. (But I would check them, either way.)
Is the AC wiring in the TT all tightly twisted together, everywhere? If the AC mains pair's wires become physically separated from each other, at all, anywhere, then the enclosed loop area forms a much better transmitting antenna. The platter and tone-arm metal will not shield the time-varying magnetic field, much at all.
If there is a transformer, etc, the same rules apply to all of the secondary wire pairs, and to any rectifier-to-caps conductor pairs.
If the wire pairs in the tone-arm are not tightly twisted, ALL the way to each end, they will be a good receiving antenna for the time-varying magnetic field from the AC wiring, or the motor itself.
If the tone-arm switches the AC on and off, make sure they didn't run just ONE of the AC wires to the switch and back. It should have BOTH wires of the AC pair, tightly twisted both there and back, going wherever either one goes! Same goes for the run to any fuse, etc.
Edit: "Tightly twisted" is more difficult for larger wire gauges. But try for at least 4 turns per inch. Tiny wires probably need more turns per inch, just for "physical integrity" (and because you can, and more twists per inch is better).
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Gootee,
this advice is wrong.
You have stated it a few times recently and I have let is pass without comment.
The flow and return pair going to the switch works just as effectively as the single flow going to the switch and the single flow returning from the switch. Twist the single flow with it's return mate, i.e just TWO wires going to the switch.
Twisting of a flow and return pair is what reduces the loop area.
Be careful at the junction point where the switch flow& return taps off from the mains cable. There is potential for a loop area there as well.
AndrewT,
You are correct. I should have said "untwisted", too. I guess I was only imagining certain scenarios where one wire got split off to go to a switch or fuse, or was daisychained to both a switch and a fuse, and then rejoined the other one via a different return route, so that it couldn't be twisted with itself. I have seen that a lot.
In this case, for example, maybe he'd find the AC pair at the entry point, then one wire going straight to the motor and the other going to a switch and then to the motor.
Yes, you could have the single wire that went to the switch come back to the point where it originally parted from the other wire, and twist it with itself during the excursion to the switch and back, and with the other wire the rest of the time. Or, you could run both wires wherever each one needed to go, keeping them twisted together as much as possible.
You are correct. I should have said "untwisted", too. I guess I was only imagining certain scenarios where one wire got split off to go to a switch or fuse, or was daisychained to both a switch and a fuse, and then rejoined the other one via a different return route, so that it couldn't be twisted with itself. I have seen that a lot.
In this case, for example, maybe he'd find the AC pair at the entry point, then one wire going straight to the motor and the other going to a switch and then to the motor.
Yes, you could have the single wire that went to the switch come back to the point where it originally parted from the other wire, and twist it with itself during the excursion to the switch and back, and with the other wire the rest of the time. Or, you could run both wires wherever each one needed to go, keeping them twisted together as much as possible.
Thanks, guys. I haven't had a chance to pull either deck and check things, but I hope to after tax day (April 15 or so). I'm convinced now that the buzz of the Dual and the hum of the Luxman are different issues, and it's the Luxman hum I'm most keen on solving. The other (Dual buzz) is, I think, a bad ground somewhere.
A quick look at the Luxman schematic makes it look like the tonearm switch is DC. The mains looks to be connected only to the speed strobe. Secondaries of the iron all look to be rectified and smoothed before anything else happens. I don't see the tonearm switch explicitly on the schematic, but as I said, except for the neon strobe on the trafo primary side, all else appears to be rectified and filtered.
Shorting the wire AND leaving it open but not connected to the cartridge both eliminate most of the hum. That's why it seems to me to be the cartridge that's picking up most of the hum. I've read that the cartridge (AT440MLa) had a run of bad production wherein hum was excessive due to a grounding problem, but I think mine post-dates that period.
If I unplug the TT mains (AC) plug, there is still some hum (same level as when the TT is plugged in but not switched on) so that part is probably related to the interconnects - if I disconnect the signal cables, there's no noise (shorted or not) except for some hiss.
So it's complicated. Signal cables are picking up hum. Cartridge is picking up hum (more and more as it approaches the DD motor under the spindle). The neon TT strobe is causing hum. I'm sure I'll have to work to minimize each of these and hope that the end result is a livable level of hum.
A quick look at the Luxman schematic makes it look like the tonearm switch is DC. The mains looks to be connected only to the speed strobe. Secondaries of the iron all look to be rectified and smoothed before anything else happens. I don't see the tonearm switch explicitly on the schematic, but as I said, except for the neon strobe on the trafo primary side, all else appears to be rectified and filtered.
Shorting the wire AND leaving it open but not connected to the cartridge both eliminate most of the hum. That's why it seems to me to be the cartridge that's picking up most of the hum. I've read that the cartridge (AT440MLa) had a run of bad production wherein hum was excessive due to a grounding problem, but I think mine post-dates that period.
If I unplug the TT mains (AC) plug, there is still some hum (same level as when the TT is plugged in but not switched on) so that part is probably related to the interconnects - if I disconnect the signal cables, there's no noise (shorted or not) except for some hiss.
So it's complicated. Signal cables are picking up hum. Cartridge is picking up hum (more and more as it approaches the DD motor under the spindle). The neon TT strobe is causing hum. I'm sure I'll have to work to minimize each of these and hope that the end result is a livable level of hum.
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