Tube PHONO preamp interference - RFI, EMI, bad grounding?


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. 




That photo showing a 33 ohm resistor partially encased in yellow shrink wrap looks like very amateurish work. Could be the ill advised work of a previous owner. Also, is that resistor connected at its other end? If not, it’s not doing a blessed thing.

You never mentioned whether tightening the transformer laminations, etc, had a beneficial effect on noise emanating from the chassis (not the noise that we started out talking about which contaminates your audio signal).

At this point you’re  receiving a lot of advice of questionable merit, apart from posts by Atma-sphere. If you don’t have or can’t access local expert help, I suggest you pay attention to Atma.

@filipm thanks for posting those pics. Very interesting..yes, if you want to put it back together the way it was you may need a new 33 ohm resistor, but those are cheap enough. That one looks like a Vishay-Dale metal film, which are often found in audio because of how quiet they are.

I searched the web for images of the EAR 834p to see if I could find some that did not have the resistor, but of the ones that I found were a good enough pic to see the wiring in this spot of the EAR - all had the resistor there. So it seems intentional.

This one appears to have the same resistor as yours..(you may have to click the plus sign cursor once to increase its size)

This one does as well.

This one is a great pic, with what appears to be a "standard" (cheaper) metal film resistor between the ground post inlet and the IEC ground, and appears to be connected to the PCB ground plane directly (which would then match your EAR if I read things correctly).

Look at the first one again though at the RCA input jacks - there is some component they have bypassing signal to ground - a capacitor perhaps for noise filtering? Showing my inexperience here, I have not seen a capacitor that looks like that, perhaps one of the more expert folks on the thread can tell us what it is. Likely a custom mod (especially considering the Hovland MusiCap capacitors in there that I am reasonably sure are not stock given their cost).


I live near a major Air Force Base and occasionally get interference (although mostly on FM) from one of the radars on the base.  The periodicity of the noise to me is a giveaway that it is something causing a "sweep".  What that might be you are better to guess than me.

If you examine the schematic that someone else posted above, you can see there is a 33 ohm resistor shown in the schematic as a series element in a CRC filter for the filament supplies. I don’t know how you could have been measuring the resistance across that resistor, given your description of where you placed your probes, but if your probe was touching something that you could not see that was on one side of that resistor and the other probe was on the other side of that resistor, then you could have measured it inadvertently. Maybe you should retest that resistance between the two probes that you’ve earlier reported and which atmosphere remarked upon. That’s the only 33 ohm resistance that I cansee in the schematic, but of course you might be measuring the parallel sum of two or more other resistances.