Massive buzz when using CJ PV10A with NAD C372

The plug on this thing is three pronged; I cannot invert power. I did try moving it off the common power strip and plug it into the same wall socket directly. Frankly, I would have been surprised if it improved things. It didn't.

When the CJ is run as an AUX input, the humm is ever present, even when the CJ is not powered.

Unfortunately, I don't have an oscilloscope or a good multimeter that will go down into the millivolt ac and dc ranges. Nothing registers on my household meter but that doesn't say much. The NAD itself is silent ... very very black when on a channel with no input signal. Put it on AUX and I cannot get it above 2 on a scale of 1 to 10 before it wants to shutdown.

My father is quite fond of saying, "The right tool for the right job is invaluable." Now, I have a gift certificate for a local electronics store ... . "Hey, Honey, I need to talk with you."

Any more ideas?

Hmmm...the fact that it hums even when the CJ is not powered precludes the idea of DC being the problem. So it must be a ground issues, as you surmised.

Here is something you could try that has worked for me in the past: Take a wire, any old thin guage wire like bell wire or stranded lamp cord wire, strip an end and wrap it around one of the CJ's chassis screws and put the screw back in so that the wire is pinched in place. With the other end of the wire, do the same on the NAD. If the NAD has a phono ground post, that will work great.

Then see if that solves the problem. Connecting the two chassis together will make sure they are at the same ground potential. If this doesn't work, it might be the CJ's or the NAD's ground is isolated from the chassis but I doubt this is the case since you have a loud hum. If you are willing, give it a try and see what happens. Keep me posted.

PS, I too always say you have to have the right tool for the job. No doubt about it! It takes a quality meter to measure millivolts indeed.

A

While a mile or two above ground today travling across the country, I was struck by a thought. The CJ has a three pronged power cord. All of the other equipment is two pronged. I can well imagine my problem resulting from a slight difference in the potential from the safety grounmd and the negative line seen by the power supply. Tying the two chasis together as you suggest, Aball, sounds promising. Another quick fix to try would be simply to remove the safety ground from by using an adaptor. That's not a long term solution, though.

When I get back from business travel later this week I will try your suggestion.

BTW, know of any good sources for reasonably good but relatively inexpensive oscilloscopes? Something well under $200 would be nice. This is the type of problem that awakens long forgotten electrical engineering studies. I'd love to have had one to use for this problem.

Cheers!

No dice. I tried connecting the two chasis together. The noise is still there. I tried isolating the ground leg on the power cord. The noise grew which didn't surprise me.

Now I havea new symptom. I cannot get a signal from my CD through the CJ preamp to the AUX channel on the NAD. I can play the CD via either the NAD AUX and CD inputs. Inserting the CJ only gives me backround humm. I've toggled the source/tape switch without effect. The Source Selection is clearly set on CD and levels are well above minimum. Nothing but the humm.

I'm not sure what to do from here. My very limited tube knowledge comes basic electrical engineering classes 20 years ago. I wouldn't mind learning, I just need some pointers on where to start. (Truth be said, I have considered building a tube pre-amp as a project once I convinced myself that I could hear differences.)

I've wondered from time to time if the Vandersteen high-pass filter between the pre-amp and the amp was introducing humm, but if it were the case, I would expect it on all channels.

I now think that someting is actually broken in the CJ and that the nature of break was settled in in starges. A few days ago I had humm but could get a signal through the CJ to the NAD on its AUX channel. Now I cannot even do that.

Thoughts?

Yeah, sounds like there is something wrong with the CJ. That it too bad but Lew Johnson is a swell guy and he can get it fixed, no problem.

Arthur