Wanting to understand better how the PSM156 presents to the incoming AC and the power supplies of connected components, I asked Mike for more details. "As we discussed in Germany, there is no voodoo in our box, just the application of long-known principles laid down by the forefathers of our understanding of electricity, Faraday, Henry, Hertz et al. These ordinary principles are implemented with overriding attention to the sonic result. Whilst starting with the math and lab measurements, we always let our ears be the final overriding arbiter. As such there was no priority to design the ultimate brick-wall filter to ruthlessly block all frequencies above 50-60Hz or to achieving the maximum decibels of attenuation to produce an impressive specification sheet. Rather, it was to lower noise in all ways that made a positive sonic contribution whilst avoiding the pitfalls of restricting dynamics by strangling the power path. That's how we came to incorporate a number of separate elements to gradually suppress the offending frequencies over many gentle stages rather than throttle them out in one go.
"The basic armoury available to us was the same as it is for all who work in the mains filter/purifier game. Capacitors shunt with different enthusiasm at different frequencies according to their capacitance and to an extent their construction. Coils impede the path of different frequencies according to their inductance value and to an extent construction. And so you end up with a box of capacitors and coils. The art is to optimize their use, layout, materials, types etc. to enable connected components to operate at their absolute peak whilst taking nothing away from the raw punch and power that is available to us straight out of the wall.
"Looking into our box, the coil windings are 13 with two windings per donut, one side treating the live line, the other neutral for common-mode interference. The two larger outboard single windings do one for live and one for neutral to deal with differential-mode interference. The box-shaped components are the shunting capacitors, the two very smallest for common-mode interferences on the live and neutral lines, all others for differential-mode interferences. We adopted a design path of first creating an overall 'main wash' section which substantially cleans up the power by removing DC offset and cleaning up the earth line. This cleansed symmetrical power is then fed to a 'rail' facilitating equal resistance paths to six independent power conditioners in their own right, each serving the six power outlets."
"In the 'main wash' section we have 3 spike arrestors for lightning protection, 5 coil windings and 8 shunting capacitors in addition to the DC offset correction circuit of the semiconductors under the heat sink and the electrolytic capacitor bank. So this section has 16 filter elements + the DC circuit. Each of the separate conditioner circuits dedicated to each output has 4 coil windings and 3 shunt capacitors for 7 filter elements. And so in a straight-through path each output has its power treated by 16 + 7 = 23 elements plus the DC removal. But each output also benefits from the fact that because each connected piece of equipment attaches to its own dedicated conditioner before joining the cleansed equal power rail, cross contamination from back interference by one connected component to another cannot occur. Interference from each piece of equipment is a very real problem. Even the simplest linear power supplies have their bridge diodes chopping at the waveform, never mind switch-mode supplies. So in actuality each output benefits either directly or indirectly from all 58 filtering elements plus the DC offset circuit in the overall box."
Having once been struck by lightning in Cyprus—my ears were actually ringing for hours—the master circuit breaker had tripped fast enough to protect our hifi gear but three hand sets and two answering machines had melted because the over-voltage came in through the phone line. I was thus curious whether Puritan's spike protection is sacrificial. "For the spike arrestors we recently changed from metal-oxide varistors to gas-discharge types. We think that incorporating lightning protection is a good call for this type of accessory although many people use MOV specified at too low a voltage such that they are being constantly 'ticked' by the mains peaks to affect the waveform. This forms part of the criticism of poorly designed/specified conditioners which also makes them far more prone to sacrificial failure. When we used MOV, they took care of spikes over 1kV—lesser spikes would be arrested by other components—so they were not impinging in any manner on the mains waveform. The gas-discharge devices we now use provide 9'000 amperes of spike protection to your equipment and can accept hundreds of very high current zaps and happily carry on. If they are correct that lightning never strikes twice, all should be very well."
Delivery of the 15A/3'500Va box was by styrofoam-sleeved double box inside 2 meters of green bubble wrap via ParcelForce which once in Ireland rode with our standard postal service. The very slinky power cord with 20A IEC for a more secure fit came dressed in a loose black sleeve rather than the orange brown in the stock photo. I'd asked for a UK wall plug and US sockets on the device itself. And that's how it came. Puritan can do all global power receptacles including—very rare for high-end makers—the peculiar Swiss socket I could never find whilst we lived in CH. "We launched our power cord in a 'copper' jacket but got so many requests for black that that has become more our standard. However, we still do copper and also white to suit a customer's requirements, taste and domestic harmony."
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