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Audiophile components
 

 

 

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 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".

Why is this the case?

To illustrate this, lets follow the signal on it's path from the CD player through to the loudspeaker system, and ultimately to the human aural system. We will assume a reasonably respectable amplifier with less than 0,01% total harmonic  and  less than 0.01% intermodulation distortion.

 The voltage level of the audio signal from the CD player appears at the input leg of the first capacitor in the amplifier chain as several hundred millivolts rms. Lets say, 440mV r.m.s., the old domestic line level. (Nowadays its usually a lot higher at around 2V r.m.s.)  This  originated in a recording studio from electrical signals fed to a mixer desk via a set of microphones. Already the signal has passed through scores of capacitors. The composite signal is recorded onto a master tape or disc and then stamped onto your CD as a series of miniscule digitally encoded bumps and troughs. The undulations are read by a laser and converted from digital form to analogue form as a varying voltage. At the input of the amplifier , the harmonic and intermodulation distortion level in the source music is well above the distortion and background noise level of the amplifier.   Now let us consider the distortion caused by a  'non-audiophile quality, capacitor' in the signal chain. The level of the capacitor distortion components relative to the source distortion is hundreds of times lower.  In fact,  in our decent amplifier, it is well below the noise floor. You couldn't possibly hear it.  Looked at another way. If the total harmonic distortion in the signal is 3% (a very conservative figure) and the total harmonic distortion (THD) of the amplifier is a mere 0.01%, (which includes the much lower distortions from the capacitor), it doesn't take a genius to see that mucking about changing capacitors for the sake of it, won't make any audible difference.   

Now let's follow the signal out of the amplifier:

 The signal travels from the amplifier as an amplified voltage and current through the speaker cable to the loudspeaker's speech coil. This causes a changing magnetic flux in the coil which interacts with the fixed flux in the gap between the coil and speaker magnet to create cone motion. This in turn creates sound pressure waves. Here the total harmonic and intermodulation distortion leaps up even further. A figure of 5% would again be very conservative.   The non-linearities inherent in the loudspeaker to human aural system, makes any capacitor distortion look like a nit on a gnat's eye lash.  First in the loudspeaker, the non-linear conversion of  changing current to changing magnetic flux adds appreciable levels of distortion. Then the non-linear conversion of magnetic force to motion in the cone adds even more. The conversion of cone motion to sound pressure waves adds more still. Finally your own set of aural receptors, non linearly convert the sound pressure waves into electrical nerve impulses in the brain.  You own ears add considerably more distortion than the difference between two capacitor types.

A much more serious distortion, more like an interference, occurs in some male brains. This blurs the original thought of inserting a CD, relaxing, and listening to the music. Instead thoughts of that nasty non-oil filled capacitor, loom in the brain.               

The truth is, the distortion, compression and background noise of most CD & Vinyl  recordings plus the non-linear distortions in the loudspeaker-aural system, has hundreds of times greater effect on the original sound than the effect of changing a resistor or capacitor to an audiophile type. That non-faulty component is innocent ! Leave it alone (unless of course its faulty) and enjoy the music! In some cases, changing to audiophile capacitors can actually decrease performance see polypropylene versus oil filled blog polyprop V OF.

 When we service a typical vintage amplifier we often replace all the electrolytic capacitors and  several resistors, not because they are 'better'  so called, 'audio quality types' types but because many have deteriorated. i.e., either one or more of , low value, o/c, s/c, leaky, high ESR etc, etc.

We insist on using high quality electronic components in all our service work for long term reliability and

 

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 path for unwanted currents e.g., noise, ripple, and signal  bypassing. To effect this, 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 and ESR can cost  several pounds! The difference audibly... there isn't any!  Those nasty ceramic capacitors we hear audiophiles ripping out of circuit and replacing by foil ones are superior for HF decoupling due to their inherently low inductance. You often see these sensibly shunting decoupling electrolytics to improve HF and spike suppression.   

Speaker cable

Solid state amplifiers have a very low output impedance relative to the speaker impedance. The output acts as a voltage source. Therefore, short  lengths of thick twin copper wire to each speaker will  make the best use of the amplifier's excellent damping factor. Valve amplifiers have much higher output impedance than solid state amplifiers, so the effect of the speaker cable resistance is much less pronounced.  In both cases, ordinary multi-strand thick twin flex is perfectly suited.

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 (i.e. several hundred times less across the cable length). (The difference in resistivity between copper wire and silver wire is not at all relevant at the lengths used. If a 3mm square section copper cable was 1km long it would have a resistance of 1.86 ohms or 3.7 ohms for twin runs. The same length solid silver twin run would have a resistance of 3.53 ohms. Thick multi-strand copper wire is perfect. Don't waste your money on silver or silver plated wire) *
  2. low inter-cable capacitance and therefore high capacitive reactance across the audio spectrum, relative to the loudspeaker impedance.  (The inter-cable capacitance of  decent low cost twin flex has a capacitive reactance way above that of the speaker impedance across the audio spectrum, so it is irrelevant)
  3. low series inductive reactance relative to the nominal speaker impedance across the audio spectrum. ( ordinary thick multi-strand loudspeaker twin flex has a negligible inductive reactance at audio frequencies)
     

To achieve the best performance use inexpensive 80 to 200 multi-strand twin (figure of eight) cable and keep the length as short as possible ( i.e., a few metres).

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

 

 

* From Pouillet's law:

R = p x l /A

'R' is the resistance in ohms.

'p' is the resistivity of the metal used (copper 1.68 x 10-8) (silver 1.59 x 10-8)

'l' is the length of the cable in metres

'A' is the x section area of the cable in metres

 

     

  

  

 

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Last modified: Monday, 27. April 2015 12:57