2. analog
  3. 127317-5312

Periodic noise

My system picks up noise every eight minutes. There is a kind of scratching mid-register ("ta-ra-ta-ta") sound that last for ten or fifteen seconds. It is similar to descriptions of "GSM buzz" but it happens regularly and regardless of whether our mobile phones are on or off. It happens when the analog source is selected, not other sources (or not obvious, in my system). It is very clear when the volume is mid-high, with no music playing. It is not from the cartridge and the tonearm cable, since it happens even when I disconnect them from the phono stage. When I disconnect the phono stage, however, I don't hear it. So it seems to be picked up from the phono stage itself. It happens across different phono stages. Shielding the cables with ferrite does not help much. It seems like a very strong signal.

Anyone recognizes this problem?
o_holter
almarg's avatar
almarg
9,670 posts
 
P.S: FWIW, I note the following statement in the datasheet for the security system device I linked to earlier, which like your device transmits every 8 minutes. This is in addition to a separate statement in the datasheet indicating compliance with FCC Part 15 requirements for a Class B digital device, which are intended to "provide reasonable protection against harmful interference in a residential installation."
Radio frequency radiation exposure information according 2.1091 / 2.1093 / OET bulletin 65
This equipment complies with FCC radiation exposure limits set forth for an uncontrolled environment.
This equipment should be installed and operated with minimum distance of 20 cm between the radiator and your body.
This transmitter must not be co-located or operating in conjunction with any other antenna or transmitter.
20 cm is about 8 inches.

Regards,
-- Al

o_holter OP
980 posts
 
Thanks, Al. The transmitter was close to 8 METERS from the system, and yet the speakers made noise like mad. I am not in the "very worried about exposure" camp, but it was quite special. It is the pulse that matters (15-20 seconds per 8:20 minutes). If the specs only give the average radiation, they won't tell the full story. Thank you for your input, I will investigate some more. 
dbtom2
383 posts
 
@almarg @o_holter 

The OP didn't say how long the interfering device had been in place or how long the interference (noise) had been perceptible. 

So my question is: Could this noise be "a canary in a coal mine?"

In other words, if the devices had been in place for awhile but the noise only recently began to be heard, would it be an indication of something failing (a noise shunting capacitor perhaps?) in the signal chain?

Not that I want to turn over too many rocks but I am curious....
almarg's avatar
almarg
9,670 posts
 
Good question, dbtom2, but I guess the answer is "no" since Mr. H stated in the OP that the issue occurred with multiple phono stages, and only when a phono stage was connected and selected.

Regards,
-- Al
 
ptss
1,964 posts
 
3 cheers for Almarg !!!
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