Hi all, appreciate all of your advice and suggestions! I've tried some of these ideas but couldn't get rid of the RFI
I sympathise - in 2020 I moved from south west to south east London, right in the shadow of several famous radio masts in Crystal Palace.
I am sure you have tried this, but the permanent fix for me was moving to properly shielded interconnects (as in, old fashioned electrical theory inspired interconnects). In my case, these:
https://www.hifisystemcomponents.com/interconnects-cables/cusat50-interconnect.html
Problem was solved.
I'd have bought these if they were in the States. Does anyone know any alternative source? I'm just using some XLR to RCA cables from Cable Matter at the moment.
I had static noise years ago found out that it caused by a pair of TP link powerline wi-fi extenders. After removing those extenders problem fixed. Hope it helps.
I had the same experience as well.
I remember reading this far up the thread the other night. Unfortunately (or fortunately) I don't have any Wi-fi extenders, and I'm running ethernet to my PC...
Yeah, I've noticed as well that the HP-8 will pick up noise from a mobile phone or wireless devices if in proximity.
Maybe a Faraday Cage could shield it?
https://backyardbrains.com/experiments/faraday
I bought some military-grade, Faraday fabric off Amazon and it unfortunately didn't work. I taped it up to cover my window, tried covering the back side of the amp, tried covering the tubes, and tried covering the entire amp, but the RF interference still leaked through. Return
That Faraday cage idea may actually work, but first, try shielded power cables and interconnects for your whole system (not necessarily expensive); possibly a power filter (I actually have one of these on order in hopes of lowering the noise floor:
Pine Tree Audio Iso-Power 15A Power Filter). Keep us posted!
This was my initial thought, that my power is not clean. I tried two different surge protectors, and plugged my amp into a Sinewave UPS running pink noise overnight, but neither got rid of the RFI

At this point, I'm grabbing one of those power filters and hoping for the best.
Just stuff you're probably already aware of:
1 - Is your cellphone anywhere near the HP8?
2 - Is your router (any Wi-Fi broadcasting component) near the HP8?
Hey Peter, thanks for asking. I usually have my phone at my desk, but for testing last night I moved it away. It helped a little bit, but I did notice that hovering and swinging my phone around the amp "warped" the RFI sound, as in, I'm bending the RFI. This morning it's not anywhere near my amp and the RFI is still here :/ I also don't have any Wi-Fi broadcasting component near the amp as my router is in another room, two walls away.
Things I've also tried the past two days and their effectiveness:
- Moving the HP8 away from the window: didn't help.
- Putting all audio components on one surge protector: didn't help.
- Ferrite chokes/beads: LOTS OF THEM. Where there is a cable, there are two chokes. What helped most was the choke on the headphone cable, coming out of the amp. This got rid of maybe 60% of the RFI.
- IFI SilentPower, GND Defender: didn't help, at all. It also didn't help the last time I got this problem, so I wouldn't recommend this stupid expensive block to anyone.
- Tylenol: helps a lot, but didn't get rid of the RFI.
- RCA Ground loop isolator: also didn't help, actually made it worse. This helped last time though.
- Different XLR to RCA cables: didn't help. But since these are longer, I could wrap them around the power transformer into a coil. This actually helped a ton and got the RFI down significantly to just background noise. Now when I listen to orchestra or film scores with lots of quiet passages, it sounds like the ADHD voices in my head. For busier genres, it's ignorable.
- This is very strange, but using my Heresy as a preamp and placing it on top of the power transformer noticeably suppressed the RFI. I don't understand the physics of this, but it was an odd phenomenon. Also having all of the components touching each other worked amazingly. Pictured is my ridiculous-looking, Frankensteined setup that reduces the RFI noise to a barely audible, whisper level.
Some observations:
- Gripping and holding the RCA cables noticeably reduced the RFI loudness, so could this be a grounding issue? But then the IFI SilentPower block and running my amp through a UPS didn't do much, so I'm not sure.
- The noise gets louder as I turn up the impedance switch. I can only listen to my Atrium and HD800s at the medium impedance setting. High impedance sounds like TV static.
- Though interestingly, this is coming from only the left channel, and it's independent of tube types. I might have to bring the amp to a local tube amp repairman and have him look at it.
What's next for me:
- Grab a good quality power conditioner/filter from Amazon per @JerseyD's recommendation. I'm thinking this Furman one for its small footprint. Does anyone have experience with a power conditioner/filter that isn't massive?
- Bring the HP8 out to the shop when I pick up my QSA. At this point, I'm hoping that there's an electrical component issue that's fixable. I mean, this is still better than dealing with invisible radio waves.
Thanks everyone for chiming in! I'll keep y'all posted if I manage to not lose it.
Edit: If nothing helps, I might have to give up, sell my HP8, and go back to solid-state... I'm open to recommendations for a comparable solid-state amp (used), at $1000 - $1500. I've been looking at the Schiit Mjolnir 3, Violetric V281, Cayin IHA-6/IHA-8, Ferrum Oor, IFI Pro ICAN, and HeadAmp GS-X MK-2.