Almighty TT hum --- help

My old time TT went humming in one channel a while back and it turned out to be defective interconnects. If your hum is in both channels your problem likely lies elsewhere.

While my TT was humming one channel, leaving the interconnects hooked up but unplugging the TT from the wall made it go away. Replacing the TT's worn RCA females didn't help. Renewing the interconnects did.

Since you've got hum on any source it sounds like the amp is the misbehaver. Maybe your amp was in storage/left unpowered for a long time?

I stowed an OK-fine SS Dynaco 120 power amp in a hot Dallas attic. A couple of years later, it powered up and still worked but the transformer hummed in the chassis. Tightening the hold down bolts didn't help. That amp had failed two times prior (over one 8 cent and one 15 cent part respectively), so my solution was to sell it at half its value to someone who was willing to isolate the hum's exact cause. Sorry it's not much help. How attached are you to the NAD?

The plot thickens; sorry I misunderstood what you meant :^)

Let's assume the hum is the sound of 60Hz house current. Connect the TT to the phono input on the NAD then unplug the TT from the wall. Without its power source I doubt the TT can induce the hum. Remove the TT from its base and look at its wiring. Check its routing to see how free it is in its travel. Any chaffed insulation? Be careful; the cartridge leads are very fine and easily damaged. Are the RCA interconnects hard wired to the TT? Check their interface with the cartridge leads. If you can replace the RCA interconnects, try another set. Does your TT mute the output before it shuts off? Check the switch that mechanically opens and closes to perform this function. Is the headshell built into the tonearm? Is it removable? Clean that interface to remove tarnish and corrosion.

The weird thing about TT's is that the signal connections are allowed to float free of chassis ground. So the grounding that usually occurs through the RCA interconnects with other components requires a separate ground wire with a TT. Grounding the amp with your hand suggests your TT ground is not getting through. This separate wire which routinely takes alot of abuse from connection and disconnection weakens at the preamp end. Mine has been hanging by a single filament at least twice in its lifetime. Cut off about a half inch or more and reterminate it with a little spade.

When mounting the TT in its base take care that the RCA interconnects run away (instead of under) the motor and its power supply. Likewise route the power cord away from the RCA interconnects. If they must cross do it at a right angle. Experiment with the routing of the ground wire under the TT. Cut more holes in the TT base to separate the power cord from the RCA interconnects.

Once I loaded the TT into its base and the motor sat right atop the power cord pinching it to the floor of the base. That made the whole equipment rack vibrate! Keep trying, you'll get it.