What makes this gap even more striking is how little data high-end brands share about their products. Once you see how industrial engineers approach the same problem, the luxury price tags start to look strange.

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Full story: https://www.headphonesty.com/2025/11/industrial-power-filters-beat-audiophile-power-conditioners/

If you use a pair of standard oscilloscope probes at 10/1 as a differential input with series capacitors of 1 nF 1000V you can safely look at the AC line.

Even if you touch the AC line after the isolation capacitors that is less than 50 micro amps of current. Well below leathal but probably enough to be educational.

Now if you want to feed a spectrum analyzer you can use capacitors feeding a voltage divider into a wide band instrumentation amplifier.

The important issue to have a high enough input impedance that the capacitor coupling will provide a high level of isolation.

Lethal current can start at 5 mA, a theory I was taught but never have tested. Normally a safety factor of 10 would be applied, but as you can do 100 quite easily that is where I would aim. Keep in mind even with a transformer has leakage capacitance.

I would also suggest you build a box to contain all the high voltage parts to maintain safety.

Of course the other method is to use an oscilloscope that is designed to measure power line distortion like the Tektronix THS735.