Almighty TT hum --- help

Rockvirgo,

Thanks so much for the detailed plan of attack. I shall go forth, put the plan into action and report back!

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.

It seems I may have misrepresented what is going on here. My cdp and tuner work perfectly with this old NAD and have since I bought it. I actually connected the TT to the tuner and aux sources and the hum was still there (got to be the TT, right?). I still have not investigated the possibility of damaged phono input jacks, but the hum just reeks of a grounding problem to me, but I can't see any problem. I'd love to borrow someone else's TT, but I don't know anyone who has one (sad, isn't it?). That way I would be sure to know which was the culprit that was causing this hum.

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?

Thanks for the responses...I just got a chance to do some more investigation today. Here are the results.

1. Using both line level sources (aux and tuner), the hum was still present, as loud and persistant as before.

2. I checked all connections to the cartridge and they appear and feel solid.

3. The hum is both channels, but using headphones, I realized that it is about 50% louder in one channel (left).

4. I disconnected the cartridge entirely and the hum sounded exactly the same.

5. I also found out (accidentally) that the hum was reduced in volume whenever I touched the amp. Does this imply a grounding problem?

I will take off the cover of the amp and see if the phono input jacks have been damaged in some way. Any other suggestions would help. I'd like to think that the TT is the problem (that way MAYBE I can justify buying a new one). I have heard that the 3020 has a good phono stage for its low cost and I definitely had that in mind when I bought it.

What does it sound like with the cartridge disconnected?

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.

When I ran into a similar hum trying to use phono inputs which had not previously been used, it turned out that the preamp female phono input jack of one channel had been detached from its internal soldered continuity with the preamp by someone in the past violently twisting off the male jack on the end of the cable from the turntable. This was a hum heard in both channels even though one jack was at fault.

Try the NAD w a line level source. that should help you isolate it. Also check cart leads.