RFI!!!!

[milosz]

I live in the same building as an FM radio station.  There is a certain amount of RFI that I can hear using ANY phone preamp, just so happens I am using my Eros at the moment.

The setup I'm using for testing this is a VPI Scout, Dynavector 10X5, EROS, and a CRACK/SPEEDBALL headphone amp.
All cables are 12-inch "Blue Jean" low capacitance cables, Beyer DT880 600 ohm headphones.

With the Crack gain set to a normal listening level, when I lift the stylus from the LP  I hear the distinct buzz of RFI along with very faint mumbling of the FM station's audio.

When I touch the ground point on the VPI Scout with a finger the level of this RFI goes down about 6 dB. Moving the Scout and Eros around changes the character of the sound and increases / decreases the level a little bit.  Playing with wires running from the Scout ground lug to AC third pin safety ground at the wall socket - as I move the wire around to take it over to the socket, the level of RFI goes up and down, the harmonics of the buzz change, etc etc. Connecting the wire to the third pin doesn't do anything.

Removing the input cables from the EROS, the RFI drops to  the noise floor of the EROS. I'd estimate that the RFI noise is ~10 dB louder than the residual noise of the Eros. Removing the phono signal ground from the  Eros or the turntable lug makes the RFI worse.

Using a different phono preamp (Parasound Z-Phono) made no difference.  Using different signal cables made no difference.  Changing from the Crack / Beyer DT-880's to a Stax SRM-T1 and Stax SR-007 headphones made no difference.  Chaning the arrangement of AC cords from all plugged into a powerstrip to all plugged directly into wall socket made no difference.

Am I going to have to listen to vinyl inside a Faraday cage? 

[Paul Birkeland]

What arm is on your TT?

[johnsonad]

Sounds like it's time to move that radio station out of the building!

[Grainger49]

I'm trying to understand.  The radio station/studio is in the building.  Is the broadcast tower on the top?  There is no RF until you get to the broadcast amplifier at the tower. 

[saildoctor]

I have a similar problem - with some equipment I pick up the local NPR FM station strongly.  Seems to depend on the weather.  Do you know whether your interconnects use wire braid or foil shielding?  Foil is better at blocking out RFI.

[milosz]

The station is a LPFM (low power FM) operation, the antenna is atop the building.  They are about 50 watts I think, the antenna is perhaps 50~100 ft. from my turntable, mostly straight up.  According to their engineer, their SWR is about 1.15:1 which means there will be some RF radiated by their transmission line and by their transmitter itself.  The transmitter is about 40 feet from my turntable; walls in this building are old-school plaster with wire mesh and wood lath. Floors are wood, so no shielding there.

Arm is VPI JMW 9. 

The 1 ft long interconnects are made from Belden 1694A which has braid and foil shielding.

RF  at 100 MHz is hard to deal with. A wire to ground will typically have enough reactance to offer a fairly high impedance at 100 MHz, making it difficult to "drain off" the offending RFI to ground.  Using my 'scope I can see this VHF signal on EVERYTHING here, it's in all my audio gear, though luckily the only place I can HEAR it is in the phono preamp which is, after all, fairly high gain.  I try to use balanced interconnects whenever I can, balanced lines are better for avoiding RFI although there is still some 100 MHz RF floating on all the chassis  etc.  Can't use balanced lines for phono, or for Eros output though.

The RFI hummmmmmmbzzzz through the Eros isn't HORRIBLE  but when I am trying to compare different phono preamps it's hard to evaluate the noise floor of the preamp when there is omnipresent RFI.

[Paul Birkeland]

This might be an option:


Based on your descriptions, the best results would likely be obtained by building a "quiet room" for your turntable.  This seems to be pretty easy to accomplish by making a closet in your listening room into a DIY Faraday chamber.  (It may end up looking kind of illegal when you're done)

There also look to be some RF blocking paints available.  This might be the best solution overall, but could be difficult due to dealing with the floor. 

[Paul Joppa]

The Dynavector is a very low resistance cart, for a high-output. That probably means you can load it with tons of capacitance without affecting the audio output. (I calculate 0.068uF fro a 100kHz rolloff, at the specified 150 ohms; anything greater than 0.010uF should be hefty enough.)

So it might be worth experimenting with some caps. Ceramic CG0 types are said to be very linear and nice counding, and all ceramics have a good reputation for maintaining low impedance at very high frequencies. Mica and polystyrene are also excellent; polypropylene pretty good, don't use mylar.

I'd start with one across the input RCA jacks. Other candidates are the EF86 grid. You can experiment with grounding the other end to the nearest signal ground, or to the nearest chassis ground. (All the 5-terminal solder strips are grounded to the chassis at the middle pin...)

[milosz]

I tried a 0.1 uF ceramic cap across the input to the signal ground, this made the RFI louder, so I removed that and tried it from center pin (input) to chassis ground on the Eros, this was no different than no capacitor.

Curiously, today the RFI was not as bad as the other day when I was fooling around with this gear.  In fact, today  the inherent AC hum picked up by the cartridge was most of what I head with the arm up off the LP and the amp gain turned way up.

Maybe the FM transmitter had high SWR or something the other day and the RF was "backing up" and radiating out of their gear and transmission line- and maybe they tuned things up to reduce SWR so now more of the RF is going out of the antenna instead of being reflected back down their coax.  All transmitters radiate a little RF out of their chassis, the higher the antenna SWR the more will radiate out of the transmitter.  I'm sure their transmitter is well grounded, but at 100 MHz the cable leading down to even a very solid earth ground can have enough impedance to prevent the RF from draining off.