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as the title says I have this problem: a loud high-pitched hiss (some 4Khz I believe) coming from speakers when a line input is selected. I have searched for similar problems but all I found seems related to static background noise, which is not the case, or the low-pitched ground loop hum.

I believe it is still related to grounding, but I can't understand how (I have no understanding of electronics beyond the absolute basics).

The hiss is intermittent (going on for bouts of 10-20 seconds each, then nothing for a time between a couple minutes and an hour, then again). It goes up and down with system volume, it is high volume (clearly audible when music is being played), it is irrelevant to music actually being played and it happens consistently on all AC powered audio systems of the house:

  • Computer speakers (2.1) connected to onboard audio;
  • A turntable's line output, connected to active speakers;
  • A turntable's line output, connected to an amplifier's line input and passive stereo speakers;
  • A turntable's phono output, connected to a phono stage, then to an amplifier's line input and passive speakers;
  • Other kinds of line inputs connected to the amplifier and passive stereo speakers;
  • A bass guitar powered amplifier.

It does not happen, ever, when the amplifier is playing other sources (coaxial, optical, digital) or when the computer soundcard is connected to headphones.

The turntable mentioned above is grounded to the phono stage grounding pin, but the hiss goes away only when I personally touch the TT grounding pin. So it can be an issue with the house electric system, but I'm not sure.

Is there anything I can try before calling an electrician? Would filtered outlets, better wiring etc. help?

  • Are you using balanced connections or unbalanced? If it's unbalanced that could be an issue – Timinycricket Apr 27 '18 at 9:41
  • All connections are unbalanced. I should add that I upgraded the power strip to a shielded one and tightened up the ground connection from the amplifier to the preamp, and it helped: the hiss is at a much reduced volume now. It is still there though. – Alessandro Apr 30 '18 at 6:33
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Possibly a ground loop?

You can purchase a ground loop lifter for less than ten euro online.

Even if this isn't the issue I personally think they are a handy tool to have in the box come the day you are recording somewhere with a grounding issue.

  • I purchased a filtered power strip and a better power supply than the wall wart that came in, and the hiss disappeared. There is a low static signal now (which goes away when the music starts playing on the turntable, or when I touch the ground pin. Strangely, connecting the ground pins on the turntable and the preamp has absolutely no effect, but when I touch myself the turntable pin the static disappears. I will buy a ground loop filter, thanks for the suggestion. – Alessandro May 3 '18 at 7:53

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