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
@dpop I'm still here. Just working late last few days and haven't got the time to reply properly. I'm not sure if things are resolved but what @atmasphere mentioned sounds like the answer. I haven't got a reply from the EAR factory what are their thoughts on that 33 ohm resistance on the grounding. I'll have to find what causes that resistance and fix it. Or someone else will have to fix it for me. I'll have time to take more measurements tomorrow night. Thank you! |
@atmasphere It is pretty simple - the resistance occurs here. It's either in the wire or in the joint. But the resistance between the grounding pin of the chassis (not the inlet) and the solder joint is 0.01. I'll try to resolder the chassis ground wire to the ground pin of the inlet. @ejb14 We have tried both MM and MC settings, worked just fine. There's nothing touching the board. @dpop That silver screw is holding a plate between the transformer side and the tube side.
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@filipm Thanks for the reply Filip. Looking at the pictures you have provided so far proves to me that the chasis is *not* floating (from earth ground), as I can see the green earth ground wire is soldered directly to the rear panel banana standoff/TT ground connection screw thread. That was one thing I was questioning. I still *highly recommend* purchasing this isolation transformer from Amazon. XtremPro Hi-end Ground Loop Noise Isolator/Filter It's pretty cheap, and it's always nice to have one of these in anyone's bag of tricks, when hooking up audio pieces of equipment. Again, if you do purchase this, it gets inserted between the TT preamp output, and the preamp input the TT preamp is feeding. |
@filipm Unfortunately, I don't have the engineering and design knowledge that's required to explain why that's in the circuit. Looking at the resistor, at this point in time, if you wanted to re-insert it back into the circuit, it's going to be impossible to do that, with the lead now clipped right at the resistor. I'm not sure I would have removed it, as you say the EAR plays fine anywhere else you use it, besides when used with *your* system. That means you have a problem that's exclusive to *just your* setup. |
