28/06/2026
Stress testing a newly repaired labgruppen plm20000q amplifier.
The repair was in “one of the three” +/-200vdc output pwm-circuits.
On the main’s side, this power supply features three identical active power factor compensation circuits that are run in a 120° phase-shifted mode …so one inductor is always charging energy ,when another is discharging energy, -this way, forming a more constant current intake than a single circuit would do.
Same approach is done at the output side where three identical pulse with modulation circuits supply the +/-200 V rails that are stepped down from around 380 vDC (that the power factor compensation delivers…)
This test is performed by using music and a 4×4 ohm water cooled dummy-load.
At those levels and currents, you can actually hear the music coming out of the water…that will eventually boil…
