he’s not sure about the A/C power line polarity (rear panel switch allows “A” to “B” switching for best performance).
That’s odd the manufacturer would provide a switch for switching the AC polarity of the primary winding leads of the power transformer. If the manufacturer first checked the primary winding of the transformer for the proper polarity orientation before wiring the primary of the transformer into the circuitry of the preamp why would he add a switch?
What’s really going on?
A quote from the late Charles Hansen (M)
The other side of the coin (long)https://db.audioasylum.com/mhtml/m.html?forum=general&n=449743&highlight=correct+AC+plug+ori...Posted by Charles Hansen (M) on August 16, 2006 at 09:18:35
1) Reversed AC polarity -- All power transformers have an inherent asymmetry to their construction. The primary winding comprises multiple layers, so that one lead is connected to the innermost windings and the other lead is connected to the outermost windings. This means that one lead has a higher coupling capacitance to the core of the transformer. Please remember that the AC supply is also asymmetrical, with the neutral lead essentially being at ground potential (assuming there is not a fault in the house wiring). The result is that one orientation will give a higher AC leakage current to the chassis of the amp (and worse sound) than the other orientation.In Reply to: Equipment sabotage by misguided/ignoramus DIYers posted by vacuous on August 15, 2006 at 19:46:14:
Not all transformer manufacturers use consistent markings on their transformers so that the correct orientation can be identified, and not all amp manufacturers pay attention to this even if the transformer is correctly marked. The result is that many audio products have a random chance of being correctly oriented. I would have to assume that the amp was modded to achieve the correct orientation, thereby achieving improved sound quality.
The correct way to do this is to swap the transformer leads, and not the connections at the IEC connector. The difference is that changing the leads at the IEC connector will move the power switch and fuse from the hot side of the line to the neutral side. While this *could* increase the liklihood of shock under a very unlikely set of circumstances, in my opinion the service technician *vastly* overstated the hazard that was introduced by this mod.
Read what John Curl has to say on the subject...
If you perform the AC polarity orientation test the preamp must be isolated from all other audio equipment. Therein nothing connected to any inputs or outputs on the preamp.
Chances are the cheaper plug you use will be polarized. Therein the neutral blade on the plug is wider than the Hot blade. You will need to trim down the wider neutral blade with a pair of tin snips so you will be able to reverse the plug in the wall outlet.
You will to need to insulate the bare ground tab on the cheater plug so it does not come into contact with the grounded trim screw that holds on the wall outlet cover plate. Any type of non conductive tape will work.
FWIW... Not only can the wall outlet be wired wrong with the hot and neutral conductors reversed, DIY power cords can have the plug to IEC female connector reversed. Even power cords sold on the retail market can be/are wired wrong. Not the big name brands but those made by some guy making then in their basement or garage where the final assembled power cord is not checked with a meter or a built testing device. Several years ago there was a thread running on Audio Asylum where some of a guy’s power cords had the hot and neutral reversed.
Usually the miswired mistake is found at the IEC connector.
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