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
@filipm (Perhaps) an easy test; take your DMM and with the Ear turned off, verify connectivity between the input RCA jack shields and the ground lug (not the case necessarily) or the output RCA jack shields. On my phono stages they are all connected together.
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@ejb14 It's connected, both channels are. The grounding pin of the power input is connected, the case as well (but's it's painted so it can only be measured through the screws or one tiny spot where the paint has been scratched off) How's that possible the shorting plugs aren't working? (This pictures shows the signal wire and the groung wire of that RCA plug before I twisted them together) Is it possible that the tubes pick up the signal before it gets grounded?
@audphile1 of course not. Not even plugged in. But I powered it on when I changed the tubes and left the cage opened - to see if they all light up.
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I think your shorting plugs are doing their job, and you have verified that your input shields are properly connected to ground and that the problem lies elsewhere. Have you verified your power outlets (in the wall) have good ground? You can get a tester cheap at a hardware store. That is another difference between your place and where the EAR worked just fine. FYI, I just found this link and this guy details a lot of the steps you have done so far, including the shorting plugs. Worth a read - Trouble shooting phono amplifier and SUT noise
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@filipm 8 days later and you are exactly where you started. You have a broken or poorly designed component or the combination of the two. |
