Does the noise come out of both channels? If so is it equal out of both? You might also try moving the tubes around.
All the best.
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
@ejb14 ok, signal and ground are twisted together. But the result is the same as if I plugged a regular RCA cable - a lot louder than emtpy inputs.
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Ah - that is very telling. Of what, I am not certain, but it may suggest that your input RCAs are not connected (broken solder joint) to ground in their shields, or there is some other failure internally. If the shorting plugs are correct, it should be silent if the only problem here is RF interference. Is the sound coming from both channels? Try connecting only one output at a time (left or right) to see if one side is better than the other. To make sure you have the shorting plugs correct, check the connection by using your digital multi-meter and touching the DMM probes to the signal pin and the shield on the plugs - make sure you have a positive connection (most DMMs have a connection test feature that emits a sound or beep when there is a connection.).
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I guess there's nothing that could go wrong making the shorting plugs. I simply cut a piece of cheap RCA cable and connected the signal wire to the shielding wire. It still acts as a regular cable though, basically an antenna. I measured it with a multimeter - connecting the signal pin and the shield makes a beep. If there's something wrong in the EAR itself, how's that possible it's working everywhere else except my home? 😫 There's only one thing that made a difference so far - covering everything - the unit and the cables, mainly the cables - into a metal pot. Or making a thick aluminum sleeve for the input cables. Is it possible that there's an interference between the power cord and the output cables? But again. I tried the same cables at different places. Also, the EAR preamp has been powered with a battery. |
- 187 posts total