I have Rolls Bellari VP129 tube phono pre and a ~20 year old Technics SL-Q2 TT given to me by a neighbor, looks like it has seen battle but seems to work OK, along with a brand new Shure M97Xe cart that I installed before I learned here that it is not very hifi. I connect the Bellari to Minimax then SE onto my Manley amps. No ground problems between amp and line stage. Line level sources are quiet.
I have had a hum with this TT/pre combo since I got the pre, but I don't play much vinyl so I thought it no biggie. Now I am realizing I don't play much vinyl because of the hum which is pretty loud. I bought the cart and phono pre to start playing vinyl again.
The hum has a sharp edge to it also, not just 60Hz. It also seems to fade in and out as if some RF involved. I tried a replacement Rolls 12VAC wall wart from a local dealer, but no change. The TT has the original vinyl signal leads. I assume they are unshielded.
So I was about to dump it, but I keep remembering Fremer's review. Ain't no way this thing would be class B if it sounded like this. So either it's defective or it's my bad with a loop or something. It is a Christmas present from my young kids so I would prefer to keep and use it. It is supposed to sound pretty good and other than the noise, it does have a good sound. Google found a thread on stevehoffman.com on which many people have hum problems. Of course the interpretation of hum is subjective. It is $200 tube preamp, so a small amount of hum is expected, but shouldn't be audible unless you crank it with ear on speaker. Mine is easily heard on quiet passages while I sit 10 feet away. Even Bellari's website FAQ says poor grounding will cause hum, so they have heard the complaints from others...
OK, so on steve hoffman someone suggested a good experiment. Disconnect everything from the Bellari and just listen to background noise with headphones (It has headphone pre built-in.) I tried that and heard just tube hiss when cranked full tilt. Now we're getting somewhere.
I connected the TT signal leads only to Bellari, and there's the hum with nothing else connected. I added the ground wire, still hums. Both TT and pre are two prong mains plugs. I tried them both on the same outlet. Switching the mains polarity of the TT does improve things 20%, but not total cure.
So now I suspect the TT has some funky electricals, not the pre, after all. When I connect the TT to an old Technics 40W stereo receiver I hear no obvious hum, but there is a lot of gritty background noise so hard to tell.
Then I started experimenting with combinations. Worst hum comes from TT left signal lead connected by itself. This is very loud. Connecting Right by itself is normal amount of hum. Connecting L signal to either R or L input doesn't matter. Adding ground doesn't matter.
Lowest possible hum comes from both signals connected, TTpolarity set right, and the ground lead from TT touching signal ground, not chassis ground. When the TT ground wire is disconnected hum is less than connected to ground post but more than when touching either signal ground. If it touches ground post or any part of the chassis a major part of the hum is added back in.
I could open the TT and look around inside, but not sure what to look for or try to fix. Thanks guys for any advice!
Rich
