Basic Question, Resistors Metal Film Or Carbon Film?

Just getting the components together for my JLM99s and notice there's some bumper packs of mixed value resistors 0.25w on ebay. Some are carbon film some metal film, are any of these more audio friendly than others?
Vikki(uk)

Metal films have considerably better temperature stability, which may or may not be important depending on the location in a circuit. They are also available in tighter tolerance. This is also usually not that important except where you are wanting to match a pair or some other multiple, and then you can either get close enough right out of the bag, or at least have a better chance of finding close matches when measuring and hand-selecting individual parts.

Metal films have more snob appeal so sometimes get used in maufacturing for that reason alone, even when they are in totally non-critical sections of a circuit.

And i always thought that metal films had less thermal noise...but that could be a myth of "high end audio"...

Hi Vikki

Rumor has it metel is quieter..In reality I don't think you will notice the difference. Either should work fine.

GARY

Many Thanks.
Vikki(uk) :grin:

Metal film resistors have much better long-term stability; if having the box sound the same ten years from now is important to you, I'd go with metal film. I also find they sound clearer, which may or may not be what you want in a stomp-box!

Peace,
Paul

maneco said: "And i always thought that metal films had less thermal noise...but that could be a myth of "high end audio"..."

Thermal noise is thermal noise---the universe over. There is no such thing as excess thermal noise---in volts r.m.s. at a given temperature it is square root of 4kTRB (k = Boltzmann's constant in joules per kelvin degree, T = temp in degrees kelvin, R = resistance in ohms, and B = noise bandwidth in Hz). Or equivalently as a current noise in parallel with the resistor it is sq rt 4kTB/R, in amps r.m.s.

When you put voltage across a resistor and hence current through there can be excess noise, often with a 1/f spectrum. Metal films can be quieter in this regard---a lot depends on the quality of the end terminations.

Metal films with ionic contaminants can get nasty when there is d.c. across them and in the presence of moisture. A manufacturer in Thailand had something amiss and sent a bunch of parts of which several failed in the field in an amplifier for Ford. Unfortunately they were in deep denial and kept explaining the problem away as having loaded the wrong resistivity elements in the machine that cut the spiral groove to set the value---they claimed that it produced localized hot spots and burnout. They lost the business in the end.