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This 60 Hz hum is driving me crazy

I just got a new to me, Prima Luna Prologue Premium Integrated tube amp. Sounds great, but there is a "ear to the speaker" 60 Hz hum. Hum sounds the same if I adjust volume +-/  The only thing I have connected is a Parasound Zdac.  Speakers are Rega RS1 Here is what I have tried:

1. I disconnected the Zdac so it was just the PL connected to the speakers with no other inputs. Hum still there.

2. While Zdac still disconnected, I use a 3-to-2 prong adpater to determine if its a ground loop.  Still there.

3. The outlet is a new one added from our remodel.  So I used an extension cord and plugged into an original outlet to see if the electricity was "dirty."  Hum was still there. 

Now here some possible culprits.  

* The stereo is perhaps set up in the smallest man cave in California.  The speakers are about 2 feet away from preamp.  I will try moving speakers further. 

* I am using crappy Amazon 12 AWG cables.  I have some better ones coming from Morrow Cables. 

* The stereo is in front of the panel that our internet wiring comes in through (I am in a condo complex).  There is no wireless there, but perhaps I should set up system somewhere else to try.

* I am using the tubes from the previous owner...do I just buy a set of new tubes?  

Is there anything else I should try?  Thanks in advance.

 

comedyzen
elliottbnewcombjr
5,091 posts
 

1. prior amp, no hum?

2. reconnect old/any amp to confirm the Prima amp is the source

3. both sides, or one side? if 1, that's easier to switch things one at a time, swap tubes, swap cables, swap inputs ...  if both sides ....

4. you have your own tube tester? even without a problem, you benefit for the rest of your life with a simple tube tester.

5. temp hook prima different location, small portable speakers, portable cd player, IOW, still hums in another location?

6. if all tubes test good, contact cleaner all tube pins and sockets

 

paradisecom
262 posts
 

I had a hum years ago that I couldn't get rid of, until I removed the outlet from the wall.  It turned out that the ground wire, which is bare, was just barley touching the hot lead screw terminal in the box.  I just rearranged the Romex in the box slightly and the problem was gone.

patrickdowns's avatar
patrickdowns
486 posts
 

@russ69 

LOL re "I'm too lazy to type the whole path of isolating 60hz hum, but if that hum is "ear to the speaker", quit doing that."

I had a hum like this and spent a lot of time in 3-way chat with the designer of my preamp and builder of my amp (both very smart guys) who both said it can be a pain in the arse to troubleshoot ground loop hums. I did get it sorted out though there is still a very slight hum (reduced about 80%) with my ear directly next to the speaker. SO--I don't do that!  I can't hear it from the listening chair. I am lazy and easily frustrated so I am sure there are things I might try to eliminate it, but as I said, I am lazy!

russ69's avatar
russ69
3,360 posts
 

(reduced about 80%)

My main tools for finding a hum are a cheater plug and a pair of ground breaking RCAs. I take all my gear and put it on the floor and hook up one item at a time. I can usually find the culprit. Then I can work on that one piece of gear and find the solution. One of the toughest ones was an unpolarized two prong plug on a preamp. If it was inserted into the wall the wrong way, it would hum. The other way, no hum. Voila!

erik_squires
15,629 posts
 

Good news is that your average multi-meter will measure this quite well.  Set it to AC, measure it and call Prima Luna.

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