Design philosophy – Sutherland 20/20 User Manual

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I don’t know of any audiophile who likes power supplies that even remotely resemble ‘walwarts’. The

20/20 uses not one, but two of the wallwarts more sophisticated relatives – politely called a regulated

tabletop power supply.

To understand this choice, let’s look at AC to DC power supply elements required for no-compromise

high-end performance:


Rectify the AC to DC


Filter that DC


Use that raw DC to power a regulating DC to DC switching inverter (this stage also provides

galvanic isolation between the AC power line and the DC load)


Provide additional levels of filtering to remove the high-frequency ripple from the switching



Provide additional levels of noise isolation from the switching inverter to the load


Provide local voltage regulation right at the audio circuitry.

From an engineering viewpoint, items 1, 2 and 3 can be accomplished with a well chosen, off-the-shelf

table top power supply. It does those tasks well, reliably and at a very reasonable cost. The supplies

included with the 20/20 are rated at a MTF (Mean Time between Failure) of over 100,000 hours. They

are used at less than 10% of their rated capacity, so reliably should be even further increased. If one

were to fail, replacement is simple and inexpensive. In addition to that functionality, they are already

safety tested and approved for use all over the world. A great deal more time, effort and money could

be spent on custom circuitry – but to no performance advantage.

From an audiophile viewpoint, it is items 4, 5 and 6 that determine the quality of DC available for the

sensitive audio circuitry. That function is so important it takes up over 2/3 of each amplifier’s circuit

board area. Ten cascaded stages of passive RC filtering, provide an enormous distance from the pre-

amp area to the incoming DC power connector. There are

over 35,000 microfarads of capacitance

on each board. The electrical ‘distance’ is so great, when power is first applied, it takes over 10 sec-

onds for the power to travel thru these ten sections of filtering and reach the preamp stage. Voltage

slowly ramps up until the zener diodes clamp it to the correct value. Until that voltage is reached, the

audio output is muted. It is this section of circuitry that provides the extreme isolation from AC power

line affects.