All,

 Another point of interest is in noise contribution.   Carbon film 
 resistors inherently have a higher noise figure than metal film.
 So if noise is an issue, don't use carbon film resistors.  I believe 
 generally speaking, carbon film resistors have a noise value that is
 typically twice that of metal film.   And in most cases, it is three 
 to four times as high.   Just food for thought.


                                           Regards,

                                             Jim



> I have grown so accustomed to using metal film resistors for 
> 'everyday' applications that carbon film doesn't usually feature in my 
> thinking.
> 
> A Taiwanese manufacturer has asked whether they can substitute carbon 
> film for metal film in a design. They claim that cf costs are far 
> lower. Volumes are only moderate (1,000 - 10,000 products per year at 
> most). Most resistors are operated at far below their power and 
> voltage ratings.
> 
> My initial reaction is that whereas most resistors could technically 
> be changed to CF, the cost savings would be minimal compared to other 
> costs and that sacrificing the reliability of metal film would not be 
> worthwhile. I'm also dubious about the merits of allowing CF as they 
> would almost certainly be Chinese* sourced with unknown (indeed 
> non-existent) provenance and aimed at bottom of the market, 
> quality-irrelevant applications. (I've little doubt that there is a 
> reason that they are cheap).
> 
> Thoughts? - or recent experiences with modern CF resistors.
> Am I too prejudiced against a new 'mature' technology?
> 
> 
> 
>         Russell McMahon
> 
> * I've no doubt that when it makes sense to do so China can produce 
> products of superb quality. But I also have little doubt that the 
> burgeoning market / what the market will bear / caveat emptor / take 
> no thought for the morrow ... / aspects of the present market 
> explosion mean that quality will often be, at best, only as good as it 
> has to be. 
> 
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