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The Best Signal Resistor?

Over the past twenty years I have tried numerous types of resistors in almost every conceivable position in my own projects. Choosing the "best" signal resistor for your audio project is an alarming exercise and can lead to madness! The perceived sound quality differences of the various resistor types in audio circuits is, to some extent, subtle, subjective and personal. However, below you will find my impressions.

- Metal film resistors should be avoided. Most of them have the tendency to
   sound "cold". Ok, some metal film resistors, including Holco, Beyschlag,
   Philips and possibly some military grade types do not sound too bad, but I
   always missed some of the warmth!

- Although metal foil resistors, the "High-End" choice of many audio
   manufacturers in general sound excellent, I still find the sound somehow
   "artificial" and not really worth the high price.

- Also metal oxide resistors are not my preference, since they give a blurred
   midrange image.

- Carbon composition resistors by Allen Bradley, Vitrohm, Morganite, Ohmite,
   Xicon, Kamaya etc. sound excellent, natural and warm. They are less
   unaffected by vibration. These resistors are my preferred types, although
   tolerances and temperature stability are poor. There is also the issue of noise
   which, to my ear, is not really prominent or annoying, not even in moving coil
   amplifiers.

- Riken Ohm carbon film resistors approach almost the warmth of carbon
   composition types but without the poor noise, drift and tolerances. They are
   an excellent replacement for them!

How About Capacitors?

As to resistors, I have tried numerous types of capacitors and combinations of different types and values in my own projects. Choosing the "best" sounding capacitor or capacitor combination for an appropriate application requires a great deal of staying power. The perceived sound quality difference of various capacitor types, dielectrics and values is however clearly audible. Below you will find my preferences:

- Silvered mica is probably the most linear low value capacitor. They are most
   commonly used in high-frequency applications. In comparison to others, they
   are physically very large and expensive. I personally find the sound very good
   but in some cases not really worth the high price.

- Polystyrene and polypropylene film capacitors have excellent electrical
   properties, including high dielectric resistance and very low losses. They are
   linear and stable, but physically large. Many of these capacitors are
   metallised, meaning that the film is coated with an extremely thin layer of
   vapourised aluminium. This makes the capacitor much smaller than would
   otherwise be the case.

- Oil/ Paper capacitors were used ages ago in tube applications, and can still
   be found in many high-end audio applications today. They sound excellent,
   are mechanically robust and insensitive to vibration.

Ceramic and tantalum capacitors should be avoided at all costs for audio applications. Some popular mylar and polyester types sound ok. Most of them have the tendency to have a grainy or blurring sound. Electrolytics are mainly used as filter capacitors in power supplies. Although there is almost no alternative for supplies, I refuse as often as possible to apply electrolytics in audio circuits (except Silmic, Oscon and Black Gate types in some cases).

Electrostatic Interactions!

Capacitors and resistors being charged as well as semiconductors under operation cause a shifting electrostatic field in the protective insulation overcoat. Electrostatic fields between leads of resistors, capacitors and semiconductors cause a conductivity modulation and charge spreading which also may influence the component values.

With conductivity modulation and charge spreading, there is a noticeable distortion added to the signal. It is quite illuminating to consider what effect fluctuating values will have on final signals consisting of transients as audio have. A loss of detail results and the sound is dulled and/or blurred.

The solution is electrostatic shielding. It prevents or reduces conductivity modulation as well as eliminates the effects of charge spreading to some extent. The effect of shielding is clearly noticeable on capacitors and plastic type transistors (TO92), whereas on resistors and cables it is minimal.

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