2. analog
  3. 178857-176102

Tube PHONO preamp interference - RFI, EMI, bad grounding?

Hello!

My tube phono is picking up interference most probably from the air. It's EAR yoshino 834p, using three 12AX7 tubes. It's sounds pretty amazing and I willing to try everything to keep it. 

Here is a sample of the sound - 

 

The rest of the setup is ARC LS16 mk1, Classe CA200, Chord Qutest, Technics SL1200 with Nagaoka MP200, Tannoys D700

I have tried many things already -

- grounding the phono to the preamp, grounding the phono to a socket, covering the phono with a pot, saucepan - no change

-plugging the phono preamp alone into an integrated (Bryston B60) and removing other stuff.

- the important part is I have taken the phono to two other places and it worked perfectly fine, even with the cheapes cables.

- I haven't had any problems with previous phono preamps which were all solid state. 

- if I unplug the turntable the signal fades to about 50%

- if I try different RCA cables, there's not much of a change even they are shielded (audioquest mackenzie, supra etc.)

- the signal also fades when I grab the cables. Also works if I grab or squeeze the output cables. 

- I have tried to wrap the cables into aluminum foil, I have noticed a difference but it's still unlistenable.

- I have tried pluging in a 5 meters long RCA output cable and walked with the phono preamp around the room. It's simply like carrying an antenna. Placing the phono on the floor helps but again, the interference is still present. 

 

Do you have any suggestions what else to try? Is there some kind of grounding that would prevent the phono preamp acting like an antenna? 

I haven't tried a new set of tubes yet. 

I think the 12AX7 are simply too sensitive to all the mess in the air. The ARC LS16 preamp was catching the same signal very quietly when I took it's cover of. 

Thanks!

Filip

128x128filipm
filipm's avatar
filipm OP
55 posts
 

Hello again,

I have sold the EAR phono preamp few weeks ago. It was replaced with RCM sensor 2 phono stage (solid state).

It's a different story when it comes to the sound, there quite typical differences as in other tube vs. solid state comparisons. I'm very happy with the sound overall. 

 

Anyways, the phono works well when plugged into unbalanced mode.

I have just brought XLR cables to try the balanced mode and I get a ground loop.

The volume of the loop depends on the RCA cables used between TT and the phono stage. 

I have tried XLR cables with shortning plugs and the interesting thing is I get a loop only from the left channel. 

When I remove the plugs and leave the input without any connection, the loop is still there - not as loud though. It gets a little louder when I remove the TT ground cable. 

Any suggestion what to do? I'd like to use the balanced output of the phono, even with the loop I can tell it sounds better. 

 

 

lewm
13,148 posts
 

Dover, You wrote, directed at me, "There is 230 volts floating around - you should be more careful if you are going to give advice on this forum."  Your advice directed at me is good advice for all of us.  However, I don't see where I advised any action on the part of the OP; I was merely trying to make sense of the written and pictured information, and I wrote here what I thought was true based on that information only. 

Filip, I just read a few reviews of your new phono stage.  It is interesting to me that it claims to be balanced but offers only SE inputs (the claim is you can feed the RCA jacks in balanced mode or in SE mode), although it does have both SE and balanced outputs. Before consulting us usual suspects, why not ask your dealer or better yet the maker of the product? One question: Are you feeding the stage in balanced mode using SE cables?

filipm's avatar
filipm OP
55 posts
 

The chain is TT - RCA / single ended, shielded with separate ground wire -> RCM phono -> XLR out -> preamp

Could the problem be in the TT grounding?

The whole system is plugged into one wall outlet. 

Power amp plugged directly into the wall and the rest is on a unfiltered power strip.

 

filipm's avatar
filipm OP
55 posts
 

Ok, solved it by now. (The selector for balanced or unbalanced in the back of the RCM is for the input, not the output.)

Works fine with both RCA or XLR. Great phono stage.

The new owner seems to have no issues with the EAR 834p. The interference still remains a mystery :)

Thanks everyone for your help! 

More to discover