Paul S wrote:

Perhaps the PP in the circuit raised the residual current on the neutral and/or ground line(s)? ...shielding might still help with "hum" if the shielding was grounded in a way that dropped ground resistance/residual current on the problematic line. This notion still supposes it's a "ground loop" problem; but it also "explains" the roles of the PP and the shielding in "causing" and "solving" a hum problem.  Paul S

miab wrote:

Adrian, can you confirm whether you were using cable with shielding or without? Like you I had the buzzing go away when on battery or without PP2000 in system. It became dead silent. Then with PP2000 back in system there was buzzing. I went to all shielded cabling with PP2000 in system and it went silent again. I attributed it to ground loops not EMI.

drdna wrote:

Romy the Cat wrote: First of all I need to admit that I do not believe to people who claim that Purepower produces noise. My units are completely silent and I know other people who have completely silent Purepowers. I have no doubts that the people who report noise do have nose but I attribute the nose to their lock of competence to deal with ground loops. There is another issue – no matter now inapt Purepower folks are and how negligent their assembly and testing I do not think that they can do anything that would make the unit to have the noise while it maintaining in and out grounds and while producing proper wave. If you recall when I had in my possession my PP2000, before I sent it for repairs never to be returned, I did have some buzzing. Now my system is otherwise silent, and while group loops are always a concern, I do not think I was at fault.  As you recall, the buzz vanished when the PP2000 was unplugged and run in battery mode. Since everything was plugged into the PP2000, nothing else about the circuit was changed. The only change was basically to remove the part of the circuit internal to the PP2000 which acts to process power from the wall outlet. So, I came to conclusion that there must be faulty ground loop wiring defect inside the PP2000. The idea of faulty assembly was further suspected when the PP2000 failed outright. Of course, we will never know what actually was the issue, since when I sent it back for repairs, it disappeared and I never received a replacement.

miab wrote:

Adrian, can you confirm whether you were using cable with shielding or without? Like you I had the buzzing go away when on battery or without PP2000 in system. It became dead silent. Then with PP2000 back in system there was buzzing. I went to all shielded cabling with PP2000 in system and it went silent again. I attributed it to ground loops not EMI.

steverino wrote:

Again I would ask people who are reporting problems to state whether they have the original PP or the Plus version made in the last few years. One issue that is definitely tied to the Plus version was the overheating that a NZ customer reported. It was confirmed by PP since they directed the customer to mod their own unit. It is unclear how many similar units are out there and whether any design change on the Plus is completely effective in resolving that overheating or whether it has just been made less overt.

steverino wrote:

Again I would ask people who are reporting problems to state whether they have the original PP or the Plus version made in the last few years. I assume Adrian had an original version with a hum problem which was incautiously returned to the PP black hole. Or was Adrian's unit a Plus?

Romy the Cat wrote:

Unfortunately there is so such a thing as PurePower versions.

steverino wrote:

It would basically require discarding the original unit and sending out a PP plus in return in many cases.

steverino wrote:

I remarked at the time that PP production was returned to Canada that I was very concerned about the establishment of a new manufacturing process coupled with untested design changes by a small company. I have never seen that work successfully.

drdna wrote:

While it is true that changes are constantly being made probably from unit to unit in production at APS, the major design change occurred with the adoption of Class D circuitry in the PP Plus series. I suspect that the problems are caused by a mechanical/structural issue of the electrical circuit that is prone to failure in assembly or by damage in shipment. Maybe it would be best to just fly to their factory and pick one up in person.

steverino wrote:

The real issue is that there is no reliable repair center where statistics could be gathered on the various problems and their resolution. Romy at least can send his units back if a problem develops and PP will actually try to fix it or send him another. If my unit develops a problem that I can't resolve, it goes in the trash.