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I have a headphone amplifier that is afflicted by mains hum 50 Hz and upper harmonics, below is an FFT of the spectrum with nothing connected to its inputs.

In headphones you can clearly hear a buzz-drone sound, volume pot doesn't change its level either. Is this to do with the rectifier, single ground planes or something else? I tried two different transformers one R-core, and the other a novatel sealed one. No effect, changed out caps, still with this noise in the spectrum present.

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    \$\begingroup\$ Schematic and, probably, a photo will be required as layout will be important. \$\endgroup\$ – Transistor Jun 1 '16 at 6:15
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    \$\begingroup\$ This is clearly 50Hz, not 60Hz. What is 0dB referred to? -80dB noise floor is not unusual. \$\endgroup\$ – user207421 Jun 1 '16 at 6:19
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    \$\begingroup\$ "... spectrum with nothing connected to its inputs." Do you mean inputs open or short-circuited? If they're open you can certainly expect to pick up noise. \$\endgroup\$ – Transistor Jun 1 '16 at 7:23
  • \$\begingroup\$ If the inputs are open, short them or attach something, those are high impedance inputs and will pick all kinds of crud like antennas, if this IS with something connected at the input, you might need more filtering in your power supply. \$\endgroup\$ – Sam Jun 1 '16 at 10:16
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    \$\begingroup\$ If it was input pickup, the noise would vary with the volume control setting. Headphones are surprisingly sensitive. On one amplifier I had this, it was solved by returning the ground from the headphone socket to the right place (PSU star earth). But that was a "Practicl Wireless Texan" amp, circa 1976, may not apply to yours... \$\endgroup\$ – Brian Drummond Jun 1 '16 at 10:46
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Cut the ground after the smoothing caps and regulaltors and connected the rest of the amp's ground to the return path with a wire, buzz is gone heres the spectrum - enter image description here

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