RF Interference in analog rig

I recently moved. My old place had a brick exterior and plaster walls, and my turntable and phono preamp were in the middle of the building, with a plaster wall directly behind them. In the old place, I had no RF interference. In my new place, the gear is in front of a window.

There's a huge broadcasting tower only a few miles away, and I'm picking up radio signals. I had my phono preamp RCA output level at 12 o'clock and my headphone amp volume at 9 o'clock, and I could hear the radio very clearly. Anything higher than that on the phono preamp and the noise level was unacceptable.

I experimented with turning the phono preamp output down to 9 o'clock and the headphone amp volume to 11 o'clock, and that gave me a much more silent background, though of course now my amp is working harder to boost a lower signal. It has plenty of power for it, so maybe that's no big deal.

I don't know whether the aluminum tone arm is acting as an antenna, or whether it's the RCA cables picking up the interference, or something else. It's a tube phono preamp, and I used to have a guitar tube amp that also picked up radio interference, but I don't know if the blame lies with the tube electronics--I would think it's something else.

Any advice? My set-up is modest: Pro-Ject Debut III, Bellari VP130, Schiit Asgard, Sennheiser HD 595.

 

What kind of interconnects and phono cable are you using? Are they shielded?

 

Unfortunately the interconnect between the turntable and the phono stage is hard wired to the turntable. I don't know whether it's shielded, and that could well be the source of the problem.

The interconnect between the phono preamp and the headphone amp is a shielded Monoprice cable: http://www.monoprice.com/Product?c_id=102&cp_id=10218&cs_id=1021814&p_id=2869&seq=1&format=2

 

What happens when you unplug the TT from the phono amp?

 

The RFI is still there. I think the phono preamp power supply cable is acting as an antenna. I can attenuate the radio signal by moving the power cable.

This is not the stock power supply, it's an aftermarket RadioShack one. http://www.radioshack.com/enercell-3-12vdc-1a-ac-adapter-black/2730462.html

 

The power supply cold be it, tubes could be picking up interference too. You might have to try an original P.S. first. If that doesn'do it you may need a solidstate phono amp. I know that's not what you wanted to hear. Maybe some one else as a suggestion?

 

I had that problem once. I was also in front of a window. As I recall, I once picked up an O's baseball game. I fixed it by getting other interconnects. However, unlike in your situation, I had been using unshielded interconnects. I went to shielded. Nonetheless, I would see if I could borrow some interconnects to see if that has an impact.

 

Ever try those ferrite collars or RFI suppressors that snap around the cable? They are cheap and you can apply them in no time. Not sure it is a 100% solution, but may be worth trying.

 

Cover the window with tin foil.

 

In addition to the above suggestions, try shielding the tubes themselves (and make sure the shield is grounded).

I've often run into these situations, and I think what's happening is that the small-signal tubes are functioning as detectors, then the spurious signals get amplified in later gain stages along with the music signal to the point they become audible; I once made a single-tube radio using a 12AU7 (one triode section for detection, the other for AF amplification to drive headphones) powered by "D" batteries for a B+ of 12V which worked surprisingly well and even pulled in some AM and shortwave DX stations.

If that or the above fails to address the problem, the next step I'd probably try (someone correct me if I'm wrong please) would be a simple resistor-capacitor low-pass filter with a cutoff around 100kHz (calculators abound on the 'net); the capacitor would not be in the signal path, but the resistor is, so I'd definitely make sure to use a quality part.

 

I actually don't have the original power supply, because Bellari shipped an underpowered one. Cheap! Anyway, I recall picking up RFI on that, too. I'm interested in the Schiit Mani, so I might just go that route. Thanks for the troubleshooting.

 

I'd tried a ferrite core on the interconnects before, without result. I'll try one on the power cable.

 

It's a single-tube preamp using a 12AX7, so you may be right about the source of the problem. I have no idea how to build a grounded shield (or any shield, for that matter), and your last paragraph is sailing far above my head. I'm a consumer, not an electrical engineer.

 

Should I be putting them on the interconnects? or the power cables? or both?

 

Another approach would be to use a capacitor to shunt each input, thus offering a low impedance path to ground for the rf frequencies.

That said, I had a very similar problem back in 1973 when I was living in San Diego. I was down the street from KGB's broadcast antenna and I would pick them up when I made recordings. I tried a lot of different solutions and nothing worked all that well. I would also detect the station on my phones.

I tried isolation transformers (provided by the station) and noting really worked all that well. It resulted in me punching a hole in my wall out of frustration when a special recording I was making was ruined. I still have the recording.

Five years later I bought my first house, in La Mirada, a suburb of LA. I spent months looking for a house with a suitable sound room, and I finally found one with a prenominal room. The only problem is that I was now less than a mile from radio station KFI. Of course I had the same problem, but this time I use a combination of grounding and shielding techniques and pretty much eliminated it from my sound systems, but not from my telephone.

The only cool thing about this situation was that when I travelled, I could be over 1000 miles away and hear KFI coming from my neighborhood. That was pretty cool.

So back in 1992 I bought the house I'm in today. I am very clean here in terms of RF, but on occasion I used to detect ham radio from a guy one block over from me. Ironically I only picked it up out of my subs, so it was fairly easy to deal with by using LPFs. He was of very little help and pretty much told me it was my problem to deal with as he was within his rights.

Ironically, a few years ago he came down to my neighbor's house and complained that her lights were messing up his ham radio reception. He threatened to go to the FCC and she was about to spend a bundle changing her lighting systems, until I told her that we could go after him for getting into my systems. She mentioned that to him, and he of course gave up, as he remembered dealing with me years ago.

 

Tjis is a very interesting and weird problem. It definitely is an issue with the Bellari VP-130, which is cursed with a notorious background hum with the standard (cheap) power supply. Using the Radio Shack Enercell power supply (the common solution), the hum disappears, but the faint RF radio signal is amplified.

A frustrating unforced error on Bellari's part. The little red firetruck is a sweet sounding phono stage, especially with a Mullard tube. This is just Bellari being cheap bastards. They're aware of these issues, and refuse to do anything to solve them.

Fortunately, the RF signals are weak enough not to interfere notably at normal listening volume...but this shouldn't be an issue in the first place. Shame on Bellari for their laziness.

 

The world would be a better place if people could comprehend this sort of dynamic.

 

Faraday cages are built ito TV studio walls to prevent RFI.

 

I've actually got the Enercell power supply and the Mullard reissue tube. I love the sound of the Bellari VP130, but I'm itching to try the Schiit Mani. So I've put the Bellari up for sale here and on eBay. Although I'm moving again soon, and the audio rig will go in the finished basement, so maybe I'll hang on to the Bellari and try it there if it doesn't sell.

 

I really love the Bellari VP-130. With a good tube and the Radio Shack power supply, it just sings. It gives my $700 Pro-Ject Tube Box SE II a serious run for the money. My own experience, of course, so YMMV.

 

I thought it sounded great, but I got RF interference in my house. I've sold the Bellari and am going to order a Schiit Mani. In the meantime, I'm borrowing a friend's Behringer Micro Phono PP440, which sounds surprisingly good for its cost.

 

Yes! Finally the radio interference is gone from my phono rig.

What I did was to completely separate the ground wire from the interconnects between the turntable and the phono stage. Such an easy way to solve the problem

 

Forgive me for being dense, but could you kindly clarify what you did? Are you saying that you didn't connect the turntable's ground wire (which sits next to the interconnect cables) to the Bellari? Where did you put the ground wire, the stereo receiver/amplifier?

The Bellari VP-130 I purchased two years ago was a present for my Dad and the family, so I didn't have very long to solve the RF interference issue. I assume I was picking up faint radio signals because of the Bellari's position in the room, and also because the vacuum tube is exposed. If grounding could solve the issue, that would be fantastic.

 

I had a very similar issue, swapped the phono pre and no more RF at all.

Schiit Mani radio interference? »

 

I have an Avid Pulsu's and not a Bellari. Nevertheless, what I did was to make sure the ground cable is far away from the turntable interconnects between the turntable and the Avid phono stage. The ground seemed to infect the signal cables with radio interference. Strange thing is the turntable manual recommends wrapping the ground cable around the signal cables. The ground cable is connected to the phono stage.