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The other side of the coin (long)

Vacuous noted three problems with the amp. I will address the safety issues associated with two of the mods:

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.

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.

To put this into perspective, please remember that the Schuko plug used throughout Europe allows for the the AC polarity to be reversed by reversing the plug in the wall socket. In theory both sides of the AC line are supposed to be fused in this situation, but in practice this is not always done. If it were the incredibly unsafe hazard proposed by the service tech, they would have never used this system.

2) The AC safety ground was disconnected from the amp chassis -- Again, this was likely done to improve sonics. Use of an AC safety ground connected to the chassis on each component *unavoidably* creates a ground loop that will degrade sonic performance. Audible hum can be minimized (but never entirely eliminated) through careful implementation when using single-ended circuitry. Properly implemented fully-balanced systems can eliminate all residual hum, but will still suffer sonic degradation as the AC safety ground acts as an antenna to introduce RFI into the system.

The *only* comprehensive solution is to avoid the AC safety ground and use a two-wire mains connection. To do so *and* meet safety regulations requires what is known as "double insulation", but this is trivially done (as evidenced by all of the cheap Japanese receivers with two-wire power cords).

The difference between "single insulation" (as would be found in the modified ARC amp) and "double insulation" is not all that great. The double-insulated product will have a second layer of insulation in the AC power wiring that will keep the chassis from becoming live should the first layer of insulation fail. The idea is that if there is a million-to-one chance of one layer of insulation failing, then there would be a trillion-to-one chance of both layers failing at the same time.

Again to put this into perspective, there are millions of homes in this country that were built before 1960 or so and therefore lack any AC safety ground whatsoever. While this is usually not as safe as having a safety ground, it is a matter of degree and I don't think that people living in those houses should be running around in a panic, nor should the owner of a piece of audio equipment without an AC safety ground. YMMV.


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