2400 year advice
Every piece in an amp, preamp, DAC or link in the music reproduction chain matters; even the chassis itself. To believe otherwise ignores Aristotle's insight the whole is greater than the sum of its parts. For more than 2,400 years we have known that everything matters and the passive bits in our hifi products are no different. I first learned this lesson designing the original PS Audio phono preamplifier forty one years ago. Our design used a passive RIAA curve consisting of two capacitors and two resistors of exact value; their tolerance should not exceed 0.1%. Precision resistors are easy to find, capacitors are a different story. One of the capacitors was an odd value; 0.0233mF when the standard is 0.022mF. The difference between the two is small but ignoring the 0.0013mF meant a deviation from the RIAA standard we were unwilling to consider. Capacitors can be stacked together to form new values: a 0.022 and a 0.001 might get us close, but the easiest method of finding what we wanted was to hand-measure from selected bins of lower tolerance parts instead. Every designer has boxes of parts accumulated over years and ours proved a treasure chest for building prototypes during the initial design phase. The problem we kept running into was consistency of sound; even seemingly identical designs sounded different. Building matching pairs of phono preamplifiers was at a standstill until we could figure out what affected differences in sound. Each of the reference designs were identical from the viewpoint of the schematic, differing only in the parts themselves: in one we used polystyrene capacitors for the curve, the other polypropylene and in a third, ceramic; and each had a sound different from the others. It took a lot head scratching to determine the cause of sound differences between units; each measured identically. But once we settled on a common capacitor type, unit-to-unit differences vanished. This bit of insight proved invaluable as we moved forward with the design process and remains a hallmark for those building with the ear as the best piece of test equipment owned. It all matters.
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