uesday at 9:07 AM
#147
George S. said:
Question: With the dual primary transformer in the PL2000 preamp, I found lowest noise on the unit using the PC based spectrum analyzer with Line connected to the striped transformer wires and Neutral connected to the solid color wires. Has anyone looked at this on the 700 dual primary transformer. I know I wired my 400 S2 like this when I installed the IEC socket.
I have done a bunch of work in this area George. Much depends on the consistency of the winding formula that the transformer manufacturer uses. I am quite sure that PL left those details to the transformer manufacturer and did not provide them a winding sheet which would have made it a specification.
What I have found is that, generally speaking (and this all is conditioned by generally speaking because there are always exceptions):
- Transformer makers wind the primary first, closest to the core. Then layer secondaries on the outer winding layers, on top of the primary windings.
- With dual primaries, they will lay down a pair of wires at the same time to keep the primary wire lengths the same. Sometimes they use bifilar wire to do this, but not always.
- The end of both winding that starts at the core is where your hot wire should go to because these windings are farthest away from the secondaries that get layered on top of the primary windings. This will produce the lowest secondary coupling noise in a North American single phase application where the neutral wire in our homes is effectively earth ground.
- In European and other international high voltage applications. it matters much less because both primary input wires are hot. You don't get the US advantage.
- The noise is lower if you do this because you effectively have the ground end of the windings in close proximity to the secondary windings and therefore you get less capacitive and stray flux coupling noise between primary and secondary. That old trick of flipping the AC plug (before polarized plugs emerged on the scene) actually had some science behind it.
- I have done custom transformer work and provided a winding sheet to the manufacturer of the custom in order to control the winding sequence. Then I confirmed with measurements that the benefit of following the above guidelines actually does occur.
Hopefully this is helpful, and now it is documented here...
Always working on making it better...