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Audio quality electronic components

Hardly a day passes when someone doesn't phone asking if we can replace this or that component with a better quality audio quality counterpart to improve the sound quality.
It typically goes something like this, "Mr ***** from some UK audio setup has already fitted audio quality resistors  and it sounds so much better,  now I would like you to quote me to change all the capacitors for better audio quality types."

I  try hard to offer friendly advice and offer a positive solution  but it always surprises me 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 .... unless of course the said components are faulty.  Several of these chaps have spend £1000s on speaker cables too!

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 typical common garden metal film 1/2 watt resistor costs less than a penny! A typical 'audio quality' resistor costs considerably more but offers absolutely nothing audibly or electrically useful!

'Audio' capacitors are another strange recent addition to the usual family of capacitors found in some 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 just behave such that the instantaneous current through the capacitor is directly proportional to the rate of change of voltage across its plates , the value of the capacitor being a constant. Unfortunately other parameters exist on a real capacitor that mars this relationship.  Series resistance, parallel resistance, inductance, value stability with temperature and frequency, all play their part in destroying the ideal current / voltage relationship. In an audio circuit a poorly chosen capacitor type could effect the performance but the point is, a good design engineer knows what types not to use for certain functions. Even if cost is a major consideration the engineer will still not use the wrong type of capacitor, he/she may use a cheaper but non the less capable alternative.

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 question is how much?. In a well designed amplifier the answer is, " nothing, or certainly well below audible detection".

Why is this the case?

The audio signal at the input leg of the capacitor (say for this example, 200mV r.ms.), may have originated on a CD or magnetic cartridge, already the harmonic and intermodulation distortion level in the signal is well above background noise level. Now let us add the distortion from the 'non audio quality component', but hang on, the r.m.s value of the capacitor distortion relative to the signal is way, way below 200mv. In fact,  it is well below noise level. You couldn't possibly hear it.   There is another reason why the capacitor distortion is inaudible... negative feedback.  Negative feedback is present in all amplifiers even the ones that state "zero negative feedback". Negative feedback further reduces the IV irregularities due to component imperfections.

The true is, the distortion, compression and background noise of most CD recordings is hundreds of times greater than any difference changing to an audio type resistor or capacitor will make.

 When we service a typical vintage amplifier we often replace all the electrolytic capacitors and  several resistors, not because they are better types but because the original ones have deteriorated.

More examples of 'replacement for its own sake'

Lots of audio enthusiasts love changing normal electrolytic decoupling capacitors with expensive audiophile types.. why?  I don't now why!!

A decoupling capacitor passes unwanted currents to ground away from the signal path. The important function is, to offer a low impedance to unwanted currents (noise, ripple, signal  bypassing,. So the equivalent series resistance  (ESR) and inductance must be as low as possible. A typical good quality low ESR 220uF 100V decoupling capacitor costs less than 30p. A well known audiophile capacitor of the same value  can cost  several pounds! The difference audibly... there isn't any!

Speaker cable

Don't spend £100s on speaker cables. The important parameters of a speaker cable are as follows:

1. A relatively low series resistance compared to the speaker DC resistance to maximize efficiency (several hundred times less across the cable length)
   (The difference in resistivity between copper wire and silver wire is not at all relevant. Don't waste your money on silver or silver plated wire)
2. high inter-cable capacitance reactance relative to the nominal impedance at 20kHz 
3. low series inductive reactance relative to the nominal impedance at 20kHz
4. There is no measurable electrical difference between platted wire and normal thick multistrand wire at audio frequencies.  

To achieve the best performance use relatively inexpensive  80 to 200 multi-strand twin (figure of eight) cable.

80 strand 0.2mm twin speaker cable is typically around £1.20 per metre!

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Last modified: September, 2011 15:23:31