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
 

@atmasphere Thanks for the long answer. First of all, I totally agree it could be a matter of poor wiring (Even though I have tried the same TT and cables elsewhere and it was fine). But it can’t be the XLR part.

Is there a way to short the inputs without the input shorting plugs? (I have ordered them but it’s gonna take a while).

About the ARC - I have tried the same only with a Bryston B60 integrated, the noise has always been there.

The 20ft XLR cables were just an idea so I could move the phono section as far as possible from the speakers (or just to the other side of the room, possibly further from the neighbors wifi router). Otherwise I’m using 3ft Nordost Red dawn XLR between the ARC and the power amp.

@theaudioamp

It’s not only adding the RCA cable to the input but also moving the output cable around (without anything plugged into the EAR preamp)

If I have measured the right place, it’s a zero. I’m not sure what you mean by the signal ground of the phono input. If it’s the pin where the TT ground should be attached then it’s zero.

From the ground pin to the rest of the chassis the meter shows 33 ohms.

ejb14
37 posts
 

@filipm 

"Is there a way to short the inputs without the input shorting plugs? (I have ordered them but it’s gonna take a while)."

Just take a cheap RCA cable, cut off one end and twist the signal cable and the ground/shield wires together. Make two of them, one for left and one for right, then plug the other still good RCA jack ends into the INs left and right. Viola, shorting plugs. 

Paul at PS audio has a pretty good talk about it here if you want to get more detail on shorting plugs; Shorting plugs

 

 

 

 

 

curiousjim's avatar
curiousjim
4,631 posts
 

Does the noise come out of both channels? If so is it equal out of both? You might also try moving  the tubes around.

All the best.

dover
2,243 posts
 

@filipm

 

Have you tried turning off your cellphone - not flight mode - turned off completely ?

filipm's avatar
filipm OP
55 posts
 

@ejb14 ok, signal and ground are twisted together. But the result is the same as if I plugged a regular RCA cable - a lot louder than emtpy inputs. 

More to discover