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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
lewm
12,429 posts
 

Have you tried different electrical outlets in your home? What else shares the circuit that serves your audio system? Any fluorescents or LED lights in the vicinity? Any burglar alarms?

lewm
12,429 posts
 

One more thing: dimmers.  Are there any dimmers on the same circuit with your phono stage? And by burglar alarm, I meant the modern type that work through a wifi connection.

filipm's avatar
filipm OP
55 posts
 

First of all, I live in an apartment. The building is pretty spaceous so I only have direct neighbors above and below me. The livingroom has a dedicated circuit (I can turn everything off on the main switch and leave the livingroom on).

I have tried the wifi of course. I only have one led light and it was one of the first things I tried. Nevertheless, it could be another banality..

I’m not sure how strong the wifi signal of my neighbors is, it’s just if I take the preamp and move it closer to my wifi router, it doesn’t get any worse. If I open the wifi menu on my cellphone the signal looks pretty strong tho. Four of them with a full signal.

 

Rather than looking for the source I’d try to make the phono section more resistant to the interference. Sounds like it’s high frequency, right? The bass driver is moving as well sometimes, like it was trying to push 20Hz.

Do you think there’s a chance it’s coming from the electrical circuit? I called an electrician and he will bring a dedicated 12V battery that can power the preamp. But does it even count when the other components are powered from the wall?

 

And yes of course, I have tried all the sockets in the room, even sockets from another circuit.

 

So far it looks like a matter of position of the preamp.

 

I brought 6 meters xlr cables so I’ll move the whole linestage on the other side of the room, leading the cables under the carpet to the power amp.

Just to try it.

If it helps, I was actually thinking of leaving it that way even tho the cables between the preamp and power amp are gonna be 6 meters. (Paul from PS audio is using long xlr cables in their n1 listening room as well ;)

 

 

lewm
12,429 posts
 

Can be through the air, through the AC line, or through some component.  Do any of your components have a switching power supply? Is this phono stage electrically  isolated from the turntable motor?  TT motors put shmutz back on the AC line, and it's wise to isolate the TT from everything else.  Are you saying that the AC supply to your audio is isolated even from the other apartments in your building?

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cleeds
5,639 posts
 

Has this problem recently manifested itself, or have you always had it with this setup?

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