Measuring A Capacitor

I would first try taking a single interconnect and connect one input to the other. That might be enough to shield the input and if the hum stops you know it is coming from outside. If it still hums no need to sacrifice anything. Plug an interconnect into each input and on the other end gently jam something between the center pin and the outside ring to short them, piece of aluminum foil would work.

I think you got bad advice. It is very common to get hum from a phono section with a ground loop, missing ground, bad connection, etc. That section has very high gain compared to the other inputs so unless things are just right it will hum. Even leaving them with no input can cause hum.

The first thing to do is insert shorting plugs into the phono inputs. If hum goes away it is external. If it still hums your NAD has a problem.

Need shorting plugs? Go to Radio Shack and buy some cheap phono plugs and somehow connect the two lugs (solder together, short with piece of bare wire, etc.)

Sorry I wasn't clear. I meant take one interconnect and plug it into the right channel input of the phono and the other end of that same wire into the left input.

If it were mine I would short the input with the system powered up. I can't imagine a scenario where shorting an input would cause noise on the output but I suppose it won't hurt to turn it off first.

Good luck

What kind of hum/buzz are we talking about here? The kind that you have to put your ear to the speaker to hear or the kind that you walk into the room and say "whats that noise?"

You are chasing the wrong problem with the aluminum foil. You have a grounding issue. They can be very frustrating and confusing as evidenced by the fact you touch it and it goes down. I was once trying to track down a hum problem by using a clip lead to connect various points on various pieces (preamp, power amp, phono stage, turntable) and after having no luck I clipped one end on the preamp with the other end hanging in space just as place to put it while I thought about it and the hum went way down. This was very repeatable and I called in others to make sure I wasn't insane.

Almarg gives good advice on things to try but his paranoia about static being amplified 10,000 times is just that, paranoia. In order for static to jump you need quite a few volts so you aren't going to get quite a few times 10,000 volts out of your system. At worst you will get a very, very, very brief pop equivalent to a very, very, very, brief clipping of the amp. However, it could be a problem because that static discharge into the input could damage the transistors it hits, so his advice is once again good even if the reasoning why is flawed.

Please reread your own post. You did say it would be amplified 10,000 times. And it would not be "a very large transient." it would be a slight pop that clipped it for a minuscule amount of time. Look, it happens all of the time in the winter. I walk across the room to change the record and when I touch the tonearm I feel a discharge which creates a pop in the speakers. Over and over and over and over again. The tweeters still work just fine.

please reread my post. You evidently don't understand electrostatic discharge. You don't have to have a spark like the kind that jumps from your hand to the light switch for a discharge to occur, Most are never felt. For it to occur it would have to at some point jump the gap. When it did, however small it was, it would drive the system to clip for a instant. There is no way in the world that a very brief pop from the system would take out a healthy tweeter. It is however not unlikely that a static discharge through the input devices could damage one of them and that is the point that we both missed earlier. As a matter of fact, turning off the system would do nothing to protect those input devices. The static discharge through them would be the same no matter if the system was on or off. The only protection in that case would be to follow safe ESD practices.

You seem to be one of these people who loves to give advice but can't stand it when they are offered it. I stood corrected and admitted that my advice was bad because a static discharge into the input could damage the system by damaging the input devices. Suck it up and admit that this same pop would never take out a tweeter.

.