Hardly a day passes when someone doesn't phone asking if we can replace this or that component with a better audiophile counterpart in a vain attempt to improve the sound quality.We try hard to offer friendly advice and offer a positive solution but it is always surprising that some people, interestingly mostly men, (women have superior hearing anyway and seem more interested in enjoying the music), think that changing components for audio quality types will magically transform the sound, It won't . The only time it would make a difference is if the one you are replacing is faulty. What is an audio quality resistor or capacitor? It is well known that a good quality resistor should be low noise, the ohmic value should remain stable over time and over a range of temperatures, the stated value should closely match the actual value and inductive and capacitive parameters should be negligible at audio frequencies. Its prime purpose according to Ohm's law, is to drop voltage, or looked at another way, limit current. It should do this regardless of how fast the current/voltage changes. Modern metal or carbon film resistors do this admirably across the audio range and well beyond. A common garden 1% metal film 1/2 watt resistor of superb performance costs about one pence! A typical 'audio quality' 1% resistor costs several factors of ten more, but offers absolutely nothing audibly or electrically useful!'Audio' capacitors are another strange recent addition to the standard family of capacitors found on component suppliers lists. All good electronic engineers know that certain types of capacitor offer a better performance in certain applications than another. A perfect capacitor should behave such that the instantaneous current through the capacitor (ic) is directly proportional to the rate of change of voltage (dv/dt) across its plates , the value of the capacitor (C) being a constant.In mathematical terms; This should ideally apply at all temperatures and at any rate of change of voltage.Unfortunately other parameters exist on a real capacitor that mars this relationship. Series resistance, leakage resistance, inductance, value stability with temperature and frequency, all play their part in destroying the ideal current/voltage relationship. At radio frequencies the capacitor type used is crucial for the circuit to function at all. In audio circuitry, a poorly chosen capacitor type may effect the performance to a degree. Amplifier design engineers know what types not to use for certain applications. Even if cost is a major consideration, they will not use a wrong type if there is a chance it will mar the sound. For example, instead of using a polyester or polypropylene capacitor for coupling two circuits, cost say 30 pence, a 5 pence tantalum or electrolytic might be used instead. It is well know that the latter types are not so good electrically and can add a tiny amount of distortion. The crucial questions are 1/'how much?' and 2/'is it audible?. In a well designed amplifier where the capacitor types are chosen sensibly, the answers are, 1/'a relatively small amount' and 2/ 'no, its well below the noise floor".