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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
filipm's avatar
filipm OP
55 posts
 

@dpop I have tried these chains:

TT - EAR - Bryston B60

TT - EAR - Classe CP60 + CA200

TT - EAR - ARC LS16 + CA200 or REF150

TT - CP60 + CA200 (as the CP60 has a solid state phono stage) 

(the LS16 doesn't have a phono stage even tho it says "phono" on one of the lines, only SP preamps have phono stages)

the noise gets picked up only by the EAR, solid stages (I had 3, they were ok)

At first I thought the EAR was the problem but the seller told me he never experiences anything like this. So I took the EAR to my friend's place. Horrible wiring, cheap components - absolutely quiet and great sounding. 

 

Right now I have covered the input cables (TT>EAR) with a metallic sheath, there's a little improvement but I can tell it gets picked up by anything, the input, output, the grounding cable, maybe the power cord too. Maybe it's really a grounding problem as I measured 33 ohms between the grounding pin on the chassis and the grounding pin of the inlet. but I had it opened several times, the groundind pins are well soldered, I even had few capacitors changed. 

dpop
293 posts
 

Sorry, I didn't realize that the LS16 didn't have an internal TT preamp. Is there any TT noise when going into the CP60's TT input (using the existing RCA cables that you're using with the EAR setup)?

dpop
293 posts
 

I just noticed this:

>>>solid stages (I had 3, they were ok)<<<

So to be 100% sure, in your current high RFI/EMI environment, using a SS phono stage (the CP60) produces no noise? Is that correct?

dpop
293 posts
 

So to be 100% sure, in your current high RFI/EMI environment, using a SS phono stage (the CP60) produces no noise? Is that correct?

...when using the exact RCA cables you were using when hooking up the EAR?

dpop
293 posts
 

>>>I measured 33 ohms between the grounding pin on the chassis and the grounding pin of the inlet.<<<

If the piece of equipment you're referring to is the EAR, that figure should be much closer to zero ohms. If you were measuring the resistance of a wire that was maybe 100 feet in length, sure, maybe *that* figure could be 33 ohms, but it shouldn't be when measuring a connection the distance of inches, especially a ground connection.    

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