OP, wow. What an journey. Maybe it is time to start wondering if there is a problem with that particular Phono stage… you have conducted so many tests.
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
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- 187 posts total
There is no need to buy tube shields from eBay. There are several reputable vendors in the US who sell them, and will probably help you out with installation. One business is tubes and more. Another business is antique electronics in Arizona. Sure, you could wrap your entire unit in heavy duty foil. See if that helps. Probably you want to ground the foil in some way.. The foil must completely envelop the unit, top and bottom, sides and rear.
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There's actually a hint - even the output cables react to the interference. When I squeeze them, the noise changes. Let's see what an aluminum foil on the tubes does.. |
When you squeeze them, you create a ground via your body. I have a table radio in my kitchen. It reacts to the lighting over our sink, which is on the same circuit, and also to a Canary detector plugged into the same outlet. If I hold the radio antenna in my hand, the RFI noise over the radio gets much quieter. The EAR is not balanced, is it? Looks like you have an ARC linestage sitting on the floor; is that unit internally balanced? I presume the 834P is inside the green thing. Incidentally, maybe you wrote in haste, but I would not encase individual tubes in foil. Bad for cooling. That's the beauty of well designed high quality tube shields; they draw heat away from the tube and actually extend tube life, besides blocking interference. If you’re going to use foil, I would suggest just wrapping the whole chassis in foil; of course, you will eventually have to figure out how to allow for the whole device to stay cool, unless you install shields. |
- 187 posts total