I have a McAlister PP150S amp. My power supply appeared to have been handled roughly as the bottom panel was bent. This magnified the induction noise from the power supply when I first powered it on.
I removed the panel and straightend it. Then I installed four neoprene isolation mounts under the transformer. These are small, cylindrical mounts with a stud in each end. The mounts prevent most of the vibration from being transmitted to the chassis. This modification required adding a jumper ground wire from the transformer frame to the chassis since the neoprene mounts act as insulators.
These mounts are available from McMaster-Carr, part number 9376K114. Go here http://www.mcmaster.com/ and type the part number in the "Find" box. They are available in 1/4"-20 USS thread and M6 X 1 metric thread. They cost $1.39 US each and are 1/2" high. I had to enlarge the holes in the transformer and lower panel for the 1/4" USS thread studs. Metric would have been a better choice, but I had a supply of 1/4" USS nuts/washers.
I also put some dynamat on the inside of the top/bottom/front panels. I did not block the side air vent slots. These mods resulted in a considerable reduction in the inductance hum.
I suggested he work on better packaging in the future that would support the underside of that heavy power transformer. Despite having to go through this mod, I remain very pleased with the sound from this amp.
I removed the panel and straightend it. Then I installed four neoprene isolation mounts under the transformer. These are small, cylindrical mounts with a stud in each end. The mounts prevent most of the vibration from being transmitted to the chassis. This modification required adding a jumper ground wire from the transformer frame to the chassis since the neoprene mounts act as insulators.
These mounts are available from McMaster-Carr, part number 9376K114. Go here http://www.mcmaster.com/ and type the part number in the "Find" box. They are available in 1/4"-20 USS thread and M6 X 1 metric thread. They cost $1.39 US each and are 1/2" high. I had to enlarge the holes in the transformer and lower panel for the 1/4" USS thread studs. Metric would have been a better choice, but I had a supply of 1/4" USS nuts/washers.
I also put some dynamat on the inside of the top/bottom/front panels. I did not block the side air vent slots. These mods resulted in a considerable reduction in the inductance hum.
I suggested he work on better packaging in the future that would support the underside of that heavy power transformer. Despite having to go through this mod, I remain very pleased with the sound from this amp.