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Silly tread
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ebastler:

--- Quote from: 001 on November 26, 2018, 01:19:29 pm ---it is simple to recive this scream without guitar
1M open input is sufficient for this

We try few amps -- tube peavey 5150, tube fender junior and some solidstate fender
All of them squeal about 1kHz so it is some outer problem

--- End quote ---

Leaving the amp input open may be an unrealistically demanding condition. With the amp's high impedance input, that should really pick up any stray fields in the room. But guitar pickups have much lower impedance outputs, don't they? What happens if you terminate the amp input with a resistor, say 1 kOhm or 100 Ohm, to "simulate" the guitar?


--- Quote ---PS -- I see railroad at about 200 yards  :palm: Is it use some high power tonal signals in a rails?  :-//

--- End quote ---

Railroads are notorious for strong 16.7 Hz AC fields, from the overhead power lines. I have never heard about strong signals in the higher audio range.
SiliconWizard:

--- Quote from: ebastler on November 26, 2018, 01:49:06 pm ---With the amp's high impedance input, that should really pick up any stray fields in the room. But guitar pickups have much lower impedance outputs, don't they? What happens if you terminate the amp input with a resistor, say 1 kOhm or 100 Ohm, to "simulate" the guitar?

--- End quote ---

"Much lower" depends on how you define "much". And obviously depends a lot on the pickups and the presence of an additional internal preamp or not.
Most pickups have output impedances in the order of 5 to 10kohm or higher, and depending on the "mix" configuration, they could be in series and further double the output impedance. Even active pickups are usually 10kohm nominal. 1kohm or 100ohm would certainly not be realistic.

If dealing with classic single-coil pickups, the pickups themselves are still the most likely culprit. The guitar's internal wiring job can also cause problems as the messier it's done and the more loops you're bound to have. Series humbuckers have usually higher output impedance (around 2x obviously), but they pick up a lot less EMI themselves - you could still have EMI picked up by the wiring.

Benta:

--- Quote from: ebastler on November 26, 2018, 01:49:06 pm ---Railroads are notorious for strong 16.7 Hz AC fields, from the overhead power lines. I have never heard about strong signals in the higher audio range.

--- End quote ---

As the OP is in the Antarctic (apparently), the railroad issue does not exist.  :palm:

001:

--- Quote from: Benta on November 26, 2018, 08:20:48 pm ---
As the OP is in the Antarctic (apparently), the railroad issue does not exist.  :palm:

--- End quote ---

my soul in antarctic if You understand me
no goverments and no customs  and taxes

But body is still in human land with EMC problems  :-DD
Zero999:

--- Quote from: diyaudio on November 25, 2018, 08:47:01 pm ---
--- Quote from: Benta on November 25, 2018, 07:56:17 pm ---"There is always that guy" is also interested in the reasoning behind the "use another cable" advice and its relation to ground loops.
Diyaudio, please enlighten the OP and us.

--- End quote ---

enlighten your behind you so admire.  :-+

--- End quote ---
Thanks for such an intelligent well thought out response.  ::)

Changing the cable will normally make no difference at all. The only time the cable could be a problem is if it's faulty or completely unsuitable in the first place i.e. a loose connection or no shielding.
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