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RFI on Preamplifier

192.107.156.196
Posted on February 27, 2015 at 08:50:51
TimeConstant
 I would like to know if any of you out there have experienced RFI (RF Interference) problems that bleed into sensitive phono stages?

My Phono Stage makes noises that sound like Digital Cell Phone interference.

The Preamp line stage is mostly quiet with the occasional noise, but the Phono Stage is constantly making annoying staccatto buzzes and blurps (short duration pops and scratchy sounds).

I made a iPhone recording of the noises, and can share this file as an *.m4a recording.

Have ruled out noisy tubes, I have rolled dozens and the noises persist. I have Platinum Grade tubes in the Preamp now and the noises are still persistent.

Or is my house bugged by the Government :)

Ideas?

 

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Does it do it without the TT or the TT's IC connected?, posted on February 27, 2015 at 09:37:14
Nuit
 Usually it is the wiring coming in, one way or another. Often swapping interconnects, or even moving them around can stop it. Using some metal mass near the cables can also block the problem. Anything made of metal, and heavy can do. Some wrenches, a hammerhead, etc.

If you still get it with NO cables attached to the preamp, then it may be coming in on the AC cord. Try a different AC cord. Or the same heavy metal bits on the AC cord. (lots of them). Or on the preamp case over the area the phono bits are.

If it stops when you disconnect the phono IC. it may be the cable or the cartridge. Try a different cable there. and the metal bits on top of the cable. Or try moving the TT. The caartridge may be in a bad position for RF in your home. The problem may be you are in a strong signal path of a microwave tower
If none of that works.. You need a different preamp?

 

RE: RFI on Preamplifier, posted on February 27, 2015 at 09:43:35
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 You will need to ensure the case is shielded properly, you may also have to use tube shields. There may be a problem with your grounds, make sure you have continuity between the case and the ground tab on your power cord. Your AC power supply may also be really dirty, you may want to add a very good power line conditioner, a surge suppressor will not cut-it.

If all else fails, make a faraday cage out of your listening room by covering the walls with grounded hardware cloth (and wear a tinfoil hat so the CIA can't read your brain waves) :-)

 

A Faraday cage around the TT, or the preamp might suffice. nt, posted on February 27, 2015 at 09:45:49
Nuit
 .

 

RE: RFI on Preamplifier, posted on February 27, 2015 at 10:17:14
6bq5
Audiophile

Posts: 4393
Location: SF Bay
Joined: August 16, 2001
 I experienced this with an Audible Illusions Modulus 3a Preamp-
The fix I employed was two fold -
One - replace the coaxial leads from the RCA jacks to the PCB with a higher quality - 99% shield connected at both ends - wire
and Second- to add a Ferrite bead through which the new wire passes.
Now, NO RFI...
Having said this - interconnects are still a potential issue - and if you are in close proximity to a transmitter - the Faraday cage may be a valid option.

Happy tuning
Happy Listening

 

RE: Does it do it without the TT or the TT's IC connected?, posted on February 27, 2015 at 15:23:01
TimeConstant
 With the friendly advice from my fellow inmates and the OEM manufacturer of the Preamp, problem solved.

It was the Satellite Receiver decoder unit. It was putting noise on the power line.

I disconnected everything, and brought the system back one by one and voila, as soon as I connected the Satellite Decoder box, the noises returned.

Who needs Satellite when I have LP's and Reels?

Musica maestro!

 

RE: Does it do it without the TT or the TT's IC connected?, posted on February 27, 2015 at 17:26:09
TimeConstant
 Not only did the noise disappear, taking out the Satellite Box has lifted a veil on the system. Amazing how AC contamination affects the other neighbors sharing the same outlet.

 

Had this problem big time, posted on February 28, 2015 at 15:50:48
robotk
Audiophile

Posts: 422
Joined: May 23, 2003
 In fact I had to return an LFD Phono stage due to poor RFI shielding. First time I turned it on, I was hearing talk radio, clear as day, out of the speakers. Burying it inside a 500 pound walnut cabinet helped, but still didn't eliminate all the noise. The LFD was just designed with minimal shielding to RFI, I guess. I live in the middle of town, so I'm not surprised that I'm bombarded by RFI.

Returned it for a Sutherland, which is as quiet as it gets.

Short of getting a new stage, you can get RFI shielding paper and see if that helps.

Move any WIFI sources (routers, etc). as far away from the stage as possible. This also helped me.

 

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