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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

128x128filipm
perkri
888 posts
 

That’s a challenge, for sure.

Never heard any “noise” like that coming from my phono stage, or any other component for that matter.

Sounds like a radio that is trying to pick up a signal, that won’t tune.

And the beeps are odd.

As others have said, sounds like WiFi/router signal.

And as you’ve taken it elsewhere, and it works perfectly, it’s likely not a defective  phono stage. Adding the TT increases the noise, which makes sense as the cartridge will also pu the interference. 
 

Have you tried plugging another source, other than a TT, into the phono stage? Like your DAC (powered up, but with no signal/source of course…)

Just curious if that removes it. 
 

Sorry for your headache, must feel like you’re  chasing a ghost…

The EAR-834P box is a pretty solid brick of metal, which should help to shield the tubes from the interference?

Something is the source of that noise, I know you prefer to shield the gear, but hunting down the source might be an easier task.

theaudioamp
221 posts
 

It's amplitude demodulation of the envelope of a high frequency signal either RF or power. The beeps are to be expected. Source to be determined.

plumptonvinyl
49 posts
 

Are you using a streamer? 

ejb14
37 posts
 

I believe I have heard something similar to this before - twice - but both were some time ago - the first time it was definitely a router. Turned off the router, problem went away. Someone near you may have a powerful router. That would explain why you do not hear it when you take the preamp elsewhere. Try putting the EAR next to your own router and see if the sound gets worse.

The second time, if I recall correctly, I believe it was a combination of my iPhone 6 and a Grado Sonata 1 cartridge (an unshielded cart) going into a Croft Micro 25 (12AX7's) - but it was intermittent. I was trying to record and occasionally a similar noise would cut in intermittently. I put my phone in airplane mode and the problem went away. It may not manifest in another location with because your cell may be working on a different cell frequency elsewhere or your phones's GPS was turned off, or your bluetooth was not connected to anything..etc..; I do not seem to have the problem any longer with my latest iPhone.

 

 

filipm's avatar
filipm OP
55 posts
 

- I'm not using any switching power supply anymore with the dac nor with the streamer. 

- The problem with the phono preamp was there since I bought it, about three months ago. I have tried unplugging everything, even a freezer.

- Plugging in the DAC didn't do anything which basically means if I use a different turntable, it's won't solve the issue. 

- Ferrite cores are on the list, I'll definitely try the 100K grid stopper.

- Yes, I'm using a streamer but it was unplugged of course. Both the DAC and the streamer are powered from Allo Shanti linear PS. 

- Switching the phones off didn't help.

One more important thing to mention is the interference can be also received by the line stage - ARC LS16. I noticed it when I was switching tubes. It only happened when I opened the top mesh though. I'll try again now before I move the preamps to the opposite side of the room. That would confirm the signal is being caught from the air, right? 

- I have tried to bring the phono preamp closer to the wifi router, It doesn't seem to have any effect. I'll try again and share the changes. 

The strength of the signal depends on the height level of the the preamp. The higher I hold it, the stronger it is. I doesn't change above 1,5m/5ft but it changes with every inch closer to the floor below 3ft. 

I think it's the input of the preamp that is sensitive. It's even more sensitive with RCA cables plugged in. It's interesting that even with the input exposed the signal changes when I squeeze the output cables together, still, it never goes off completely. That's basically all I'm sure of right now. 

Thanks for the help, I really appreciate it. 

 

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