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Old 17th December 2016, 06:37 PM   #1
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Default interference troubleshooting

Hi I've looked for assistance on this on AudioKarma but am still stumped. Hope someone here can help!

I'd originally heard a high pitched noise in all channels in my EICO HF-81, sounding a bit like Cell Phone interference of yore ... a faint squealing noise a bit like a dot matrix printer. I recorded the sound at a loud volume through the phono stage here https://www.dropbox.com/s/21uk4b2jc4...rence.m4a?dl=0

Cleaned the pots/connections as advised and the problem still persists.

I've subsequently plugged in various solid state receivers including a Marantz 2230, Marantz 3330 + 140 preamp/amp, Pioneer SX 780 through different speakers, different power outlets and different rooms and am getting the same noises through all in varying degrees. The sound increases with turning up the volume, and listening in the preamp stages.

I've disconnected wi-fi routers, power strips and any lights that might be causing this but the problem persists. I live in an apartment building in NY. The problem started a few days ago and my neighbor has cited a strange noise in his clock radio - not sure if there's a relation. There are also somewhat new cell towers in the neighborhood but I can't imagine these are the issue.

Any other ideas to help diagnose?
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Old 17th December 2016, 07:57 PM   #2
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
Yes, it's cell-phone...given your equipments sensitivity, cell-phone bleedover has always been an issue.
Check your computer, your "available" link ups to Wi-Fi service?, no doubt in such an urban environment your get some dozen or so "picked up" as a possible Wi-Fi connection..??? same thing, cell-phones are so predominant now, & the FCC has not really done their job in requiring some buffers in frequencies, nor really successfully dealt with cell-phone "contamination" of the airwaves, no doubt a "victim" of corporate pressure & influence.
BTW, I get it here somewhat regularly, I can tell when someones cell-phone "goes off".....in our house, the house next door, or whomever is "within range" of the sensitivities of my equipment.
You could always encase your domicile in a sort of haphazard Faraday cage???



---------------------------------------------------------------------Rick.....

Last edited by Richard Ellis; 17th December 2016 at 07:59 PM.
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Old 17th December 2016, 08:15 PM   #3
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An Eico HF81. Is that a kit amp of a bygone era from Allied Radio?
I wanted an Allied kit but never had the nerve to call long distance and work out the shipping cost in advance (way before internet ordering).
Long distance calls were an hour's pay back then, maybe more if you went on hold.
RF is everywhere. I admit my country trailer 1/3 mile from the road in rural New market has less interference than my city house in downtown Jeffersonville, 30 feet from a busy corner and 4 miles from the AM radio towers of the Kentuckiana area. Two blocks from a cellphone tower. My worst problem was a CB nut who drove by emitting continuous dogs barking out Dixie.
I've retrofitted amateuristically sheilded hifi equipment with RF protection, both my dynaco ST-120, and a Japanese kit disco mixer, the RA-88a. If the enclosure has a complete steel box, then the job involves fitting parts to keep RF from coming in the various holes like AC cord, speaker terminals, line input, etc. Speaker terminals get a "zobel network" and a series 15-20 turn coil parallel a 3 to 10 ohm resistor. Analog inputs get parallel ceramic caps to ground, 33 pf to start with, most recently 68 pf. Power input gets a iron core or toroidal choke series the AC and neutral, plus the type x cap after the fuse plus a pi filter. Most of the latter can be salvaged from dead PCAT power supplies, or dead late model LED televisions.
For more gory details, see this about the mixer: Improving a "Disco mixer" to mid-fi performance
My ST120 amp had an enclosed iron core power transformer, so the chokes weren't needed. Having it very close to the AC cord entrance made twisting the wires unnecessary. It had a ceramic cap across the output of the transformer already, so I didn't have to buy an X cap. (X caps are rated for line AC service, have a UL CE or VDE symbol on them and the rated line voltage).
Best of luck exterminating your RF problem.
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Last edited by indianajo; 17th December 2016 at 08:23 PM.
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Old 17th December 2016, 11:52 PM   #4
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I think that Eico made a wide line of different types of kits.
While Allied only made a few kits. But they were very nice units.
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Old 17th December 2016, 11:58 PM   #5
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As for interference, Jim Brown is the go-to expert!
Start with (but skip the parts aimed only at Ham radio):
"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing"
http://www.audiosystemsgroup.com/RFI-Ham.pdf

about 50 more excellent papers:
Audio Systems Group, Inc. Publications
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Old 18th December 2016, 02:27 AM   #6
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thank you all. I have some reading and research to do.
I have also noticed that when I turn larger components on and off, such as my christmas tree lights or the CD player, there is a popping sound in the system - despite these appliances being on different outlets. Not sure if that reveals anything
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Old 18th December 2016, 08:57 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by waterboard View Post
thank you all. I have some reading and research to do.
I have also noticed that when I turn larger components on and off, such as my christmas tree lights or the CD player, there is a popping sound in the system - despite these appliances being on different outlets. Not sure if that reveals anything
This tells me you have a problem at the source . It/they are emitting emi. It is better to attenuate the emi at the source.
The second is that your equipment is sensitive to picking up emi.

Add passive filtering to all the cable pairs that enter your enclosure.
Ensure the enclosure is conducting and has small holes/slots.
A long slot lets in the same frequencies as a large diameter hole that has the same major dimension.

Use screened cable for the interconnects, where these are easily available. Screened mains leads and screened speaker leads are generally unavailable.
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Old 19th December 2016, 12:03 AM   #8
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Sounds more like there's a ground loop in the system TBH. Seems it's "hearing" the mains rather better than you want. It could still be RF demodulation if the amp is sensitive to EMI, but then the problem would vary a lot among different amps. Cables have been checked already?

I'd start with a barebones system - e.g. just amplifier and CD player (with 2-conductor mains cord, I hope) - and check whether the problem is still present.

Possibly stupid question: Mains voltage is nice and stable? We had a brownout in the office once, voltage went down to about half of what it should be (so ~US levels). Most things continued working, but guess whose PC went out? Yep, mine, the only one without a universal (100-240VAC) power supply. Also, a halogen light and an MFC's fuser didn't take kindly to this kind of treatment.
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Old 19th December 2016, 01:38 AM   #9
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Sometimes, it's worth looking at the OP device. It's a stereo tube amp, dating from the late 1950s. Would you really expect modern performance standards and RF or any "F" immunity? Eico HF-81 - Manual - Stereo Integrated Tube Amplifier - HiFi Engine
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Old 19th December 2016, 04:28 AM   #10
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Quote:
Originally Posted by Ian Finch View Post
Sometimes, it's worth looking at the OP device. It's a stereo tube amp, dating from the late 1950s. Would you really expect modern performance standards and RF or any "F" immunity? Eico HF-81 - Manual - Stereo Integrated Tube Amplifier - HiFi Engine
I've put about $4 parts in my 1966 design Dynaco amp (ST-120) to achieve RF silence. I salvaged some of the parts from PCAT power supplies designed to last a year and be replaced. Another $10 in parts to update the circuitry to something with modern accuracy.
These 1959 devices had transformers connectors & cases designed to last 50 years. IMHO a little DIY work to update the design to cope with a time when everybody carries a UHF radio in their pocket, is worthwhile.
OTOH my Dynaco ST70 may sound better than an Eico HF-81 did.
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